HP HPE FlexNetwork MSR Router Series User manual

HPE FlexNetwork MSR Router Series
Comware 7 MPLS Configuration Guide
Part number: 5998-8833
Software version: CMW710-R0305
Document version: 6PW106-20160308

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Contents
Configuring basic MPLS ·················································································1
Overview····························································································································································1
Basic concepts···········································································································································1
MPLS network architecture························································································································2
LSP establishment·····································································································································3
MPLS forwarding········································································································································4
PHP····························································································································································4
Protocols and standards ····························································································································5
Compatibility information····································································································································5
MPLS configuration task list·······························································································································5
Enabling MPLS ··················································································································································6
Setting MPLS MTU ············································································································································6
Specifying the label type advertised by the egress····························································································7
Configuring TTL propagation ·····························································································································8
Enabling sending of MPLS TTL-expired messages···························································································9
Enabling MPLS forwarding statistics··················································································································9
Enabling FTN forwarding statistics·············································································································9
Enabling MPLS label forwarding statistics for LSPs ················································································10
Enabling MPLS label forwarding statistics for a VPN instance································································10
Enabling split horizon for MPLS forwarding·····································································································10
Enabling SNMP notifications for MPLS············································································································11
Displaying and maintaining MPLS ···················································································································11
Configuring a static LSP ···············································································13
Overview··························································································································································13
Configuration prerequisites······························································································································13
Configuration procedure ··································································································································13
Displaying static LSPs ·····································································································································14
Static LSP configuration example····················································································································14
Configuring LDP····························································································17
Overview··························································································································································17
Terminology ·············································································································································17
LDP messages·········································································································································17
LDP operation··········································································································································18
Label distribution and control···················································································································19
LDP GR····················································································································································21
LDP NSR··················································································································································22
LDP-IGP synchronization·························································································································23
LDP FRR··················································································································································23
LDP over MPLS TE··································································································································24
Protocols··················································································································································25
Compatibility information··································································································································25
LDP configuration task list ·······························································································································25
Enabling LDP···················································································································································26
Enabling LDP globally······························································································································26
Enabling LDP on an interface ··················································································································26
Configuring Hello parameters ··························································································································26
Configuring LDP session parameters ··············································································································27
Configuring LDP backoff··································································································································29
Configuring LDP MD5 authentication···············································································································29
Configuring LDP to redistribute BGP unicast routes························································································30
Configuring an LSP generation policy··············································································································30
Configuring the LDP label distribution control mode························································································31
Configuring a label advertisement policy ·········································································································31
Configuring a label acceptance policy ·············································································································32
Configuring LDP loop detection ·······················································································································33

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Configuring LDP session protection·················································································································34
Configuring LDP GR ········································································································································35
Configuring LDP NSR······································································································································35
Configuring LDP-IGP synchronization ·············································································································35
Configuring LDP-OSPF synchronization··································································································36
Configuring LDP-ISIS synchronization·····································································································37
Configuring LDP FRR ······································································································································37
Setting a DSCP value for outgoing LDP packets·····························································································37
Resetting LDP sessions···································································································································38
Enabling SNMP notifications for LDP ··············································································································38
Displaying and maintaining LDP······················································································································38
IPv4 LDP configuration examples····················································································································39
LDP LSP configuration example··············································································································39
Label acceptance control configuration example·····················································································43
Label advertisement control configuration example·················································································47
LDP FRR configuration example··············································································································52
IPv6 LDP configuration examples····················································································································55
IPv6 LDP LSP configuration example······································································································55
IPv6 label acceptance control configuration example··············································································61
IPv6 label advertisement control configuration example··········································································65
Configuring MPLS TE···················································································71
Overview··························································································································································71
TE and MPLS TE·····································································································································71
MPLS TE basic concepts·························································································································71
Static CRLSP establishment····················································································································71
Dynamic CRLSP establishment···············································································································71
CRLSP establishment using PCE path calculation··················································································73
Traffic forwarding ·····································································································································74
Make-before-break···································································································································75
Route pinning···········································································································································76
Tunnel reoptimization·······························································································································76
Automatic bandwidth adjustment·············································································································76
CRLSP backup·········································································································································77
FRR··························································································································································77
DiffServ-aware TE····································································································································78
Bidirectional MPLS TE tunnel ··················································································································80
Protocols and standards ··························································································································80
MPLS TE configuration task list·······················································································································81
Enabling MPLS TE···········································································································································82
Configuring a tunnel interface··························································································································83
Configuring DS-TE···········································································································································83
Configuring an MPLS TE tunnel to use a static CRLSP··················································································84
Configuring an MPLS TE tunnel to use a dynamic CRLSP·············································································85
Configuration task list·······························································································································85
Configuring MPLS TE attributes for a link································································································85
Advertising link TE attributes by using IGP TE extension········································································86
Configuring MPLS TE tunnel constraints·································································································87
Establishing an MPLS TE tunnel by using RSVP-TE···············································································89
Controlling CRLSP path selection············································································································89
Controlling MPLS TE tunnel setup···········································································································91
Configuring an MPLS TE tunnel to use a CRLSP calculated by PCEs ···························································93
Configuring a PCE ···································································································································93
Discovering PCEs····································································································································94
Establishing a CRLSP by using the path calculated by PCEs·································································94
Establishing a backup CRLSP by using the path calculated by PCEs·····················································94
Configuring PCEP session parameters····································································································95
Configuring load sharing for an MPLS TE tunnel·····························································································95
Configuring traffic forwarding···························································································································96
Configuring static routing to direct traffic to an MPLS TE tunnel or tunnel bundle···································96
Configuring PBR to direct traffic to an MPLS TE tunnel or tunnel bundle················································97
Configuring automatic route advertisement to direct traffic to an MPLS TE tunnel or tunnel bundle·······97

iii
Configuring a bidirectional MPLS TE tunnel ····································································································98
Configuring CRLSP backup·····························································································································99
Configuring MPLS TE FRR····························································································································100
Enabling FRR·········································································································································100
Configuring a bypass tunnel on the PLR································································································100
Configuring node fault detection ············································································································104
Configuring the optimal bypass tunnel selection interval·······································································105
Enabling SNMP notifications for MPLS TE····································································································105
Displaying and maintaining MPLS TE············································································································105
MPLS TE configuration examples··················································································································106
Establishing an MPLS TE tunnel over a static CRLSP··········································································106
Establishing an MPLS TE tunnel with RSVP-TE····················································································111
Establishing an inter-AS MPLS TE tunnel with RSVP-TE······································································117
Establishing an inter-area MPLS TE tunnel over a CRLSP calculated by PCEs···································124
Bidirectional MPLS TE tunnel configuration example············································································128
CRLSP backup configuration example ··································································································134
Manual bypass tunnel for FRR configuration example ··········································································138
Auto FRR configuration example···········································································································144
IETF DS-TE configuration example ·······································································································150
Troubleshooting MPLS TE·····························································································································157
No TE LSA generated····························································································································157
Configuring a static CRLSP········································································158
Overview························································································································································158
Configuration procedure ································································································································158
Displaying static CRLSPs ······························································································································159
Static CRLSP configuration example·············································································································159
Configuring RSVP·······················································································165
Overview························································································································································165
RSVP messages····································································································································165
CRLSP setup procedure························································································································166
RSVP refresh mechanism······················································································································166
RSVP authentication······························································································································167
RSVP GR···············································································································································167
Protocols and standards ························································································································168
RSVP configuration task list···························································································································168
Enabling RSVP··············································································································································168
Configuring RSVP refresh······························································································································168
Configuring RSVP Srefresh and reliable RSVP message delivery································································169
Configuring RSVP hello extension·················································································································169
Configuring RSVP authentication ··················································································································170
Setting a DSCP value for outgoing RSVP packets························································································171
Configuring RSVP GR ···································································································································172
Enabling BFD for RSVP·································································································································172
Displaying and maintaining RSVP ·················································································································172
RSVP configuration examples ·······················································································································173
Establishing an MPLS TE tunnel with RSVP-TE····················································································173
RSVP GR configuration example···········································································································179
Configuring tunnel policies··········································································182
Overview························································································································································182
Configuring a tunnel policy·····························································································································182
Configuration guidelines·························································································································182
Configuration procedure·························································································································183
Displaying tunnel information·························································································································184
Tunnel policy configuration examples············································································································184
Preferred tunnel configuration example·································································································184
Exclusive tunnel configuration example·································································································184
Tunnel selection order configuration example ·······················································································185
Preferred tunnel and tunnel selection order configuration example·······················································186

iv
Configuring MPLS L3VPN ··········································································188
Overview························································································································································188
Basic MPLS L3VPN architecture ···········································································································188
MPLS L3VPN concepts··························································································································188
MPLS L3VPN route advertisement········································································································190
MPLS L3VPN packet forwarding············································································································191
MPLS L3VPN networking schemes·······································································································192
Inter-AS VPN··········································································································································194
Carrier's carrier ······································································································································198
Nested VPN ···········································································································································200
Multirole host··········································································································································201
HoVPN···················································································································································202
OSPF VPN extension·····························································································································204
BGP AS number substitution and SoO attribute····················································································206
MPLS L3VPN FRR·································································································································207
Multi-VPN instance CE···························································································································209
Protocols and standards ························································································································210
MPLS L3VPN configuration task list ··············································································································211
Configuring basic MPLS L3VPN····················································································································211
Configuration prerequisites····················································································································211
Configuring VPN instances····················································································································211
Configuring routing between a PE and a CE ·························································································213
Configuring routing between PEs···········································································································218
Configuring BGP VPNv4 route control···································································································219
Configuring inter-AS VPN ······························································································································220
Configuring inter-AS option A·················································································································220
Configuring inter-AS option B·················································································································221
Configuring inter-AS option C ················································································································222
Configuring nested VPN ································································································································224
Configuring multirole host ······························································································································225
Configuring and applying PBR···············································································································226
Configuring a static route·······················································································································226
Configuring HoVPN········································································································································226
Configuring an OSPF sham link·····················································································································227
Configuring a loopback interface············································································································228
Redistributing the loopback interface address·······················································································228
Creating a sham link ······························································································································228
Configuring routing on an MCE······················································································································229
Configuring routing between an MCE and a VPN site···········································································229
Configuring routing between an MCE and a PE ····················································································234
Specifying the VPN label processing mode on the egress PE ······································································237
Configuring BGP AS number substitution and SoO attribute·········································································238
Configuring MPLS L3VPN FRR·····················································································································238
Enabling SNMP notifications for MPLS L3VPN ·····························································································240
Displaying and maintaining MPLS L3VPN·····································································································240
MPLS L3VPN configuration examples···········································································································242
Configuring basic MPLS L3VPN············································································································242
Configuring MPLS L3VPN over a GRE tunnel·······················································································247
Configuring a hub-spoke network ··········································································································251
Configuring MPLS L3VPN inter-AS option A ·························································································258
Configuring MPLS L3VPN inter-AS option B ·························································································262
Configuring MPLS L3VPN inter-AS option C·························································································267
Configuring MPLS L3VPN carrier's carrier in the same AS ···································································274
Configuring MPLS L3VPN carrier's carrier in different ASs ···································································282
Configuring nested VPN·························································································································289
Configuring multirole host ······················································································································298
Configuring HoVPN································································································································300
Configuring an OSPF sham link·············································································································307
Configuring MCE····································································································································311
Configuring BGP AS number substitution······························································································316
Configuring BGP AS number substitution and SoO attribute·································································320

v
Configuring MPLS L3VPN FRR through VPNv4 route backup for a VPNv4 route ································323
Configuring MPLS L3VPN FRR through VPNv4 route backup for an IPv4 route ··································325
Configuring MPLS L3VPN FRR through IPv4 route backup for a VPNv4 route ····································327
Configuring IPv6 MPLS L3VPN ··································································330
Overview························································································································································330
IPv6 MPLS L3VPN packet forwarding ···································································································330
IPv6 MPLS L3VPN routing information advertisement ··········································································331
IPv6 MPLS L3VPN network schemes and functions ·············································································331
Protocols and standards ························································································································332
IPv6 MPLS L3VPN configuration task list······································································································332
Configuring basic IPv6 MPLS L3VPN············································································································332
Configuring VPN instances····················································································································332
Configuring routing between a PE and a CE ·························································································335
Configuring routing between PEs···········································································································340
Configuring BGP VPNv6 route control···································································································341
Configuring inter-AS IPv6 VPN······················································································································342
Configuring inter-AS IPv6 VPN option A································································································343
Configuring inter-AS IPv6 VPN option C································································································343
Configuring multirole host ······························································································································344
Configuring and applying IPv6 PBR·······································································································344
Configuring an IPv6 static route·············································································································345
Configuring an OSPFv3 sham link·················································································································345
Configuring a loopback interface············································································································345
Redistributing the loopback interface address·······················································································345
Creating a sham link ······························································································································346
Configuring routing on an MCE······················································································································346
Configuring routing between an MCE and a VPN site···········································································346
Configuring routing between an MCE and a PE ····················································································351
Configuring BGP AS number substitution and SoO attribute·········································································355
Displaying and maintaining IPv6 MPLS L3VPN·····························································································355
IPv6 MPLS L3VPN configuration examples···································································································356
Configuring IPv6 MPLS L3VPNs············································································································356
Configuring an IPv6 MPLS L3VPN over a GRE tunnel··········································································363
Configuring IPv6 MPLS L3VPN inter-AS option A·················································································366
Configuring IPv6 MPLS L3VPN inter-AS option C·················································································371
Configuring IPv6 MPLS L3VPN carrier's carrier in the same AS···························································377
Configuring multirole host ······················································································································385
Configuring an OSPFv3 sham link·········································································································387
Configuring IPv6 MCE····························································································································391
Configuring BGP AS number substitution······························································································396
Configuring BGP AS number substitution and SoO attribute·································································401
Configuring MPLS L2VPN ··········································································404
Overview························································································································································404
Basic concepts of MPLS L2VPN············································································································404
MPLS L2VPN network models···············································································································405
Remote connection establishment·········································································································406
Local connection establishment·············································································································407
PW types················································································································································407
Control word···········································································································································409
MPLS L2VPN interworking·····················································································································409
PW redundancy······································································································································410
Multi-segment PW··································································································································410
VCCV·····················································································································································412
Compatibility information································································································································412
MPLS L2VPN configuration task list ··············································································································412
Enabling L2VPN·············································································································································413
Configuring an AC··········································································································································413
Configuring the interface with Ethernet or VLAN encapsulation····························································414
Configuring the interface with PPP encapsulation·················································································414
Configuring the interface with HDLC encapsulation···············································································414

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Configuring a cross-connect ··························································································································415
Configuring a PW···········································································································································415
Configuring a PW class··························································································································415
Configuring a static PW··························································································································415
Configuring an LDP PW·························································································································416
Configuring a BGP PW ··························································································································416
Configuring a remote CCC connection ··································································································418
Binding an AC to a cross-connect··················································································································419
Configuring PW redundancy··························································································································419
Configuring static PW redundancy·········································································································420
Configuring LDP PW redundancy··········································································································420
Configuring interworking for a cross-connect·································································································421
Enabling SNMP notifications for L2VPN PW ·································································································422
Displaying and maintaining MPLS L2VPN·····································································································422
MPLS L2VPN configuration examples···········································································································423
Configuring local MPLS L2VPN connections·························································································423
Configuring IP interworking over local MPLS L2VPN connections························································424
Configuring a static PW··························································································································426
Configuring an LDP PW·························································································································429
Configuring IP interworking over an LDP PW························································································433
Configuring a BGP PW ··························································································································436
Configuring a remote CCC connection ··································································································440
Configuring an intra-domain multi-segment PW ····················································································444
Configuring an inter-domain multi-segment PW ····················································································447
Configuring VPLS ·······················································································453
Overview························································································································································453
Basic VPLS architecture ························································································································453
VPLS implementation·····························································································································454
H-VPLS··················································································································································456
Hub-spoke networking ···························································································································458
Compatibility information································································································································458
VPLS configuration task list ···························································································································459
Enabling L2VPN·············································································································································459
Configuring an AC··········································································································································460
Configuring a VSI···········································································································································460
Configuring a PW···········································································································································461
Configuring a PW class··························································································································461
Configuring a static PW··························································································································461
Configuring an LDP PW·························································································································462
Configuring a BGP PW ··························································································································462
Configuring a BGP auto-discovery LDP PW··························································································464
Binding an AC to a VSI ··································································································································466
Configuring UPE dual homing························································································································466
Configuring static PW redundancy·········································································································466
Configuring LDP PW redundancy··········································································································467
Configuring MAC address learning················································································································468
Enabling SNMP notifications for L2VPN PW ·································································································468
Displaying and maintaining VPLS··················································································································468
VPLS configuration examples························································································································470
Static PW configuration example···········································································································470
LDP PW configuration example·············································································································474
BGP PW configuration example·············································································································476
BGP auto-discovery LDP PW configuration example············································································480
H-VPLS using MPLS access configuration example ·············································································485
Hub-spoke VPLS configuration example ·······························································································489
H-VPLS UPE dual homing configuration example·················································································492
Configuring L2VPN access to L3VPN or IP backbone································498
Overview························································································································································498
Conventional L2VPN access to L3VPN or IP backbone········································································498
Improved L2VPN access to L3VPN or IP backbone··············································································499

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Configuring conventional L2VPN access to L3VPN or IP backbone ·····························································500
Configuring improved L2VPN access to L3VPN or IP backbone···································································500
Configuring an L2VE interface···············································································································501
Configuring an L3VE interface···············································································································501
Displaying and maintaining L2VPN access to L3VPN or IP backbone··························································502
Improved L2VPN access to L3VPN or IP backbone configuration examples················································502
Access to MPLS L3VPN through an LDP MPLS L2VPN·······································································502
Access to IP backbone through an LDP VPLS······················································································508
Configuring MPLS OAM··············································································513
Overview························································································································································513
MPLS ping··············································································································································513
MPLS tracert··········································································································································513
BFD for MPLS········································································································································513
Periodic MPLS tracert····························································································································514
Protocols and standards ································································································································514
Configuring MPLS OAM for LSP tunnels·······································································································514
Configuring MPLS ping for LSPs ···········································································································514
Configuring MPLS tracert for LSPs········································································································515
Configuring BFD for LSPs······················································································································515
Configuring periodic MPLS tracert for LSPs ··························································································516
Configuring MPLS OAM for MPLS TE tunnels ······························································································516
Configuring MPLS ping for MPLS TE tunnels························································································516
Configuring MPLS tracert for MPLS TE tunnels·····················································································516
Configuring BFD for MPLS TE tunnels ··································································································517
Configuring MPLS OAM for a PW··················································································································517
Configuring MPLS ping for a PW···········································································································518
Configuring BFD for a PW······················································································································518
Displaying MPLS OAM ··································································································································521
BFD for LSP configuration example···············································································································522
Configuring MPLS protection switching ······················································525
Overview························································································································································525
Protection switching triggering modes ···································································································525
Protection switching modes ···················································································································525
Path switching modes····························································································································526
Protocols and standards ································································································································526
Compatibility information································································································································526
MPLS protection switching configuration task list··························································································527
Enabling MPLS protection switching··············································································································527
Creating a protection group ···························································································································527
Configuring PS attributes for the protection group·························································································529
Configuring command switching for the protection group··············································································530
Configuring the PSC message sending interval ····························································································530
Displaying and maintaining MPLS protection switching·················································································530
MPLS protection switching configuration example·························································································531
Network requirements····························································································································531
Configuration procedure·························································································································532
Verifying the configuration······················································································································534
Document conventions and icons·······························································535
Conventions···················································································································································535
Network topology icons··································································································································536
Support and other resources ······································································537
Accessing Hewlett Packard Enterprise Support ····························································································537
Accessing updates·········································································································································537
Websites ················································································································································538
Customer self repair·······························································································································538
Remote support······································································································································538
Documentation feedback ·······················································································································538

viii
Index···········································································································540

1
Configuring basic MPLS
Multiprotocol Label Switching (MPLS) provides connection-oriented label switching over
connectionless IP backbone networks. It integrates both the flexibility of IP routing and the simplicity
of Layer 2 switching.
Overview
MPLS has the following features:
•High speed and efficiency—MPLS uses short- and fixed-length labels to forward packets,
avoiding complicated routing table lookups.
•Multiprotocol support—MPLS resides between the link layer and the network layer. It can
work over various link layer protocols (for example, PPP,ATM, frame relay, and Ethernet) to
provide connection-oriented services for various network layer protocols (for example, IPv4,
IPv6, and IPX).
•Good scalability—The connection-oriented switching and multilayer label stack features
enable MPLS to deliver various extended services, such as VPN, traffic engineering, and QoS.
Basic concepts
FEC
MPLS groups packets with the same characteristics (such as packets with the same destination or
service class) into a forwarding equivalence class (FEC). Packets of the same FEC are handled in
the same way on an MPLS network.
Label
A label uniquely identifies an FEC and has local significance.
Figure 1 Format of a label
A label is encapsulated between the Layer 2 header and Layer 3 header of a packet. It is four bytes
long and consists of the following fields:
•Label—20-bit label value.
•TC—3-bit traffic class, used for QoS. It is also called Exp.
•S—1-bit bottom of stack flag.A label stack can contain multiple labels. The label nearest to the
Layer 2 header is called the top label, and the label nearest to the Layer 3 header is called the
bottom label. The Sfield is set to 1 if the label is the bottom label and set to 0 if not.
•TTL—8-bit time to live field used for MPLS loop prevention.
LSR
A router that performs MPLS forwarding is a label switching router (LSR).

2
LSP
A label switched path (LSP) is the path along which packets of an FEC travel through an MPLS
network.
An LSP is a unidirectional packet forwarding path. Two neighboring LSRs are called the upstream
LSR and downstream LSR along the direction of an LSP. As shown in Figure 2, LSR B is the
downstream LSR of LSRA, and LSR A is the upstream LSR of LSR B.
Figure 2 Label switched path
LFIB
The Label Forwarding Information Base (LFIB) on an MPLS network functions like the Forwarding
Information Base (FIB) on an IP network. When an LSR receives a labeled packet, it searches the
LFIB to obtain information for forwarding the packet. The information includes the label operation
type, the outgoing label value, and the next hop.
Control plane and forwarding plane
An MPLS node consists of a control plane and a forwarding plane.
•Control plane—Assigns labels, distributes FEC-label mappings to neighbor LSRs, creates the
LFIB, and establishes and removes LSPs.
•Forwarding plane—Forwards packets according to the LFIB.
MPLS network architecture
Figure 3 MPLS network architecture
An MPLS network has the following types of LSRs:
•Ingress LSR—Ingress LSR of packets. It labels packets entering into the MPLS network.
•Transit LSR—Intermediate LSRs in the MPLS network. The transit LSRs on an LSP forward
packets to the egress LSR according to labels.

3
•Egress LSR—Egress LSR of packets. It removes labels from packets and forwards the
packets to their destination networks.
LSP establishment
LSPs include static and dynamic LSPs.
•Static LSP—To establish a static LSP, you must configure an LFIB entry on each LSR along the
LSP. Establishing static LSPs consumes fewer resources than establishing dynamic LSPs, but
static LSPs cannot automatically adapt to network topology changes. Therefore, static LSPs
are suitable for small-scale networks with simple, stable topologies.
•Dynamic LSP—Established by a label distribution protocol (also called an MPLS signaling
protocol).A label distribution protocol classifies FECs, distributes FEC-label mappings, and
establishes and maintains LSPs. Label distribution protocols include protocols designed
specifically for label distribution, such as the Label Distribution Protocol (LDP), and protocols
extended to support label distribution, such as MP-BGP and RSVP-TE.
In this document, the term "label distribution protocols" refers to all protocols for label distribution.
The term "LDP" refers to the RFC 5036 LDP.
A dynamic LSP is established in the following steps:
1. A downstream LSR classifies FECs according to destination addresses.
2. The downstream LSR assigns a label for each FEC, and distributes the FEC-label binding to its
upstream LSR.
3. The upstream LSR establishes an LFIB entry for the FEC according to the binding information.
After all LSRs along the LSP establish an LFIB entry for the FEC, a dynamic LSP is established for
the packets of this FEC.
Figure 4 Dynamic LSP establishment

4
MPLS forwarding
Figure 5 MPLS forwarding
As shown in Figure 5, a packet is forwarded over the MPLS network as follows:
1. Router B (the ingress LSR) receives a packet with no label. Then, it performs the following
operations:
a. Identifies the FIB entry that matches the destination address of the packet.
b. Adds the outgoing label (40, in this example) to the packet.
c. Forwards the labeled packet out of the interface GigabitEthernet 2/0/2 to the next hop LSR
Router C.
2. When receiving the labeled packet, Router C processes the packet as follows:
a. Identifies the LFIB entry that has an incoming label of 40.
b. Uses the outgoing label 50 of the entry to replace label 40 in the packet.
c. Forwards the labeled packet out of the outgoing interface GigabitEthernet 2/0/2 to the next
hop LSR Router D.
3. When receiving the labeled packet, Router D (the egress LSR) processes the packet as follows:
a. Identifies the LFIB entry that has an incoming label of 50.
b. Removes the label from the packet.
c. Forwards the packet out of the outgoing interface GigabitEthernet 2/0/2 to the next hop LSR
Router E.
If the LFIB entry records no outgoing interface or next hop information, Router D performs the
following operations:
a. Identifies the FIB entry by the IP header.
b. Forwards the packet according to the FIB entry.
PHP
An egress node must perform two forwarding table lookups to forward a packet:
•Two LFIB lookups (if the packet has more than one label).
Router A Router B
Ingress Router C Router D Egress Router E
Router F
IP:10.1.1.1
MPLS network
IP:10.1.1.140 IP:10.1.1.1 50 IP:10.1.1.1
GE2/0/1 GE2/0/2
GE2/0/1
GE2/0/2
GE2/0/1
GE2/0/2
FIB table
LFIB table
LFIB table
NexthopDest Out intOut label
10.1.0.0 GE2/0/240 Router C
Nexthop
Router D Out int
GE2/0/2
Out label
50
Oper
Swap
In label
40
Nexthop
Router E Out int
GE2/0/2
Out label
--
Oper
Pop
In label
50

5
•One LFIB lookup and one FIB lookup (if the packet has only one label).
The penultimate hop popping (PHP) feature can pop the label at the penultimate node, so the egress
node only performs one table lookup.
A PHP-capable egress node sends the penultimate node an implicit null label of 3. This label never
appears in the label stack of packets. If an incoming packet matches an LFIB entry containing the
implicit null label, the penultimate node pops the top label and forwards the packet to the egress
node. The egress node directly forwards the packet.
Sometimes, the egress node must use the TC field in the label to perform QoS. To keep the TC
information, you can configure the egress node to send the penultimate node an explicit null label of
0. If an incoming packet matches an LFIB entry containing the explicit null label, the penultimate hop
replaces the top label value with value 0, and forwards the packet to the egress node. The egress
node gets the TC information, pops the label of the packet, and forwards the packet.
Protocols and standards
•RFC 3031, Multiprotocol Label Switching Architecture
•RFC 3032, MPLS Label Stack Encoding
•RFC 5462, Multiprotocol Label Switching (MPLS) Label Stack Entry: "EXP" Field Renamed to
"Traffic Class" Field
Compatibility information
Commands and descriptions for centralized devices apply to the following routers:
•MSR1002-4/1003-8S.
•MSR2003.
•MSR2004-24/2004-48.
•MSR3012/3024/3044/3064.
Commands and descriptions for distributed devices apply to MSR4060 and MSR4080 routers.
MPLS configuration task list
Tasks at a glance
(Required.) Enabling MPLS
(Optional.) Setting MPLS MTU
(Optional.) Specifying the label type advertised by the egress
(Optional.) Configuring TTL propagation
(Optional.) Enabling sending of MPLS TTL-expired messages
(Optional.) Enabling MPLS forwarding statistics
(Optional.) Enabling split horizon for MPLS forwarding
(Optional.) Enabling SNMP notifications for MPLS

6
Enabling MPLS
Before you enable MPLS, perform the following tasks:
•Configure link layer protocols to ensure connectivity at the link layer.
•Configure IP addresses for interfaces to ensure IP connectivity between neighboring nodes.
•Configure static routes or an IGP protocol to ensure IP connectivity among LSRs.
To enable MPLS:
Step Command Remarks
1. Enter system view. system-view N/A
2. Configure an LSR ID for the
local node. mpls lsr-id lsr-id
By default, no LSR ID is configured.
An LSR ID must be unique in an
MPLS network and in IP address
format. As a best practice, use the
IP address of a loopback interface
as an LSR ID.
3. Enter the view of the interface
that needs to perform MPLS
forwarding. interface interface-type
interface-number N/A
4. Enable MPLS on the interface. mpls enable By default, MPLS is disabled on the
interface.
Setting MPLS MTU
MPLS adds the label stack between the link layer header and network layer header of each packet.
To make sure the size of MPLS labeledpackets is smaller than the MTU of an interface, configure an
MPLS MTU on the interface.
MPLS compares each MPLS packet against the interface MPLS MTU. When the packet exceeds the
MPLS MTU:
•If fragmentation is allowed, MPLS performs the following operations:
a. Removes the label stack from the packet.
b. Fragments the IP packet. The length of a fragment is the MPLS MTU minus the length of the
label stack.
c. Adds the label stack to each fragment, and forwards the fragments.
•If fragmentation is not allowed, the LSR drops the packet.
To set an MPLS MTU for an interface:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter interface view. interface interface-type
interface-number N/A
3. Set an MPLS MTU for the
interface. mpls mtu value By default, no MPLS MTU is set
on an interface.
The following applies when an interface handles MPLS packets:

7
•MPLS packets carrying L2VPN or IPv6 packets are always forwarded by an interface, even if
the length of the MPLS packets exceeds the MPLS MTU of the interface. Whether the
forwarding can succeed depends on the actual forwarding capacity of the interface.
•If the MPLS MTU of an interface is greater than the MTU of the interface, data forwarding might
fail on the interface.
•If you do not configure the MPLS MTU of an interface, fragmentation of MPLS packets is based
on the MTU of the interface without considering MPLS labels. An MPLS fragment might be
larger than the interface MTU and be dropped.
Specifying the label type advertised by the egress
In an MPLS network, an egress can advertise the following types of labels:
•Implicit null label with a value of 3.
•Explicit null label with a value of 0.
•Non-null label.
For LSPs established by a label distribution protocol, the label advertised by the egress determines
how the penultimate hop processes a labeled packet.
•If the egress advertises an implicit null label, the penultimate hop directly pops the top label of a
matching packet.
•If the egress advertises an explicit null label, the penultimate hop swaps the top label value of a
matching packet with the explicit null label.
•If the egress advertises a non-null label, the penultimate hop swaps the top label of a matching
packet with the label assigned by the egress.
Configuration guidelines
As a best practice, configure the egress to advertise an implicit null label to the penultimate hop if the
penultimate hop supports PHP. If you want to simplify packet forwarding on the egress but keep
labels to determine QoS policies, configure the egress to advertise an explicit null label to the
penultimate hop. Use non-null labels only in particular scenarios. For example, when OAM is
configured on the egress, the egress can get the OAM function entity status only through non-null
labels.
As a penultimate hop, the device accepts the implicit null label, explicit null label, or normal label
advertised by the egress device.
For LDP LSPs, the mpls label advertise command triggers LDP to delete the LSPs established
before the command is executed and re-establishes new LSPs.
For BGP LSPs, the mpls label advertise command takes effect only on the BGP LSPs established
after the command is executed. To apply the new setting to BGP LSPs established before the
command is executed, delete the routes corresponding to the BGP LSPs, and then redistribute the
routes.
Configuration procedure
To specify the type of label that the egress node will advertise to the penultimate hop:
Step Command Remarks
1. Enter system view. system-view N/A
2. Specify the label type
advertised by the egress to
the penultimate hop.
mpls label advertise
{ explicit-null | implicit-null |
non-null }
By default, an egress advertises
an implicit null label to the
penultimate hop.

8
Configuring TTL propagation
When TTLpropagation is enabled, the ingress node copies the TTL value of an IP packet to the TTL
field of the label. Each LSR on the LSP decreases the label TTL value by 1. The LSR that pops the
label copies the remaining label TTL value back to the IP TTL of the packet. The IP TTL value can
reflect how many hops the packet has traversed in the MPLS network. The IP tracert facility can
show the real path along which the packet has traveled.
Figure 6 TTL propagation
When TTLpropagation is disabled, the ingress node sets the label TTLto 255. Each LSR on the LSP
decreases the label TTL value by 1. The LSR that pops the label does not change the IP TTL value
when popping the label. Therefore, the MPLS backbone nodes are invisible to user networks, and
the IP tracert facility cannot show the real path in the MPLS network.
Figure 7 Without TTL propagation
Follow these guidelines when you configure TTL propagation:
•As a best practice, set the same TTL processing mode on all LSRs of an LSP.
•To enable TTL propagation for a VPN, you must enable it on all PE devices in the VPN. Then,
you can get the same traceroute result (hop count) from those PEs.
To enable TTL propagation:
Step Command Remarks
1. Enter system view. system-view N/A

9
Step Command Remarks
2. Enable TTL
propagation. mpls ttl propagate { public |
vpn }
By default, TTL propagation is enabled only
for public-network packets.
This command affects only the propagation
between IP TTL and label TTL. Within an
MPLS network, TTL is always copied
between the labels of an MPLS packet.
Enabling sending of MPLS TTL-expired
messages
This feature enables an LSR to generate an ICMP TTL-expired message upon receiving an MPLS
packet with a TTLof 1. If the MPLS packet has only one label, the LSR sends the ICMP TTL-expired
message back to the source through IP routing. If the MPLS packet has multiple labels, the LSR
sends it along the LSP to the egress, which then sends the message back to the source.
To enable sending of MPLS TTL-expired messages:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable sending of MPLS
TTL-expired messages. mpls ttl expiration enable By default, this function is
enabled.
Enabling MPLS forwarding statistics
Enabling FTN forwarding statistics
FEC-to-NHLFE map (FTN) entries are FIB entries that contain outgoing labels used for FTN
forwarding. When an LSR receives an unlabeled packet, it searches for the corresponding FTN entry
based on the destination IPaddress. If a match is found, the LSR adds the outgoing label in the FTN
entry to the packet and forwards the labeled packet.
To enable FTN forwarding statistics:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter RIB view. rib N/A
3. Create a RIB IPv4 address
family and enter RIB IPv4
address family view. address-family ipv4 By default, no RIB IPv4
address family is created.
4. Enable the device to
maintain FTN entries in the
RIB. ftn enable By default, the device does not
maintain FTN entries in the
RIB.
5. Enable FTN forwarding
statistics for a destination
network. mpls-forwarding statistics
prefix-list prefix-list-name
By default, FTN forwarding
statistics is disabled for all
destination networks.

10
Enabling MPLS label forwarding statistics for LSPs
MPLS label forwarding for LSPs forwards a labeled packet based on its incoming label.
Perform this task to enable MPLS label forwarding statistics for LSPs and MPLS statistics reading.
Then, you can use the display mpls lsp verbose command to view MPLS label statistics.
To enable MPLS label forwarding statistics:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable MPLS label
forwarding statistics for the
specified LSPs.
mpls statistics { all | [ vpn-instance
vpn-instance-name ] { ipv4
ipv4-destination mask-length | ipv6
ipv6-destination prefix-length } |
static | te ingress-lsr-id tunnel-id }
By default, MPLS label
forwarding statistics are disabled
for all LSPs.
3. Enable MPLS label
statistics reading, and set
the reading interval. mpls statistics interval interval By default, MPLS label statistics
reading is disabled.
Enabling MPLS label forwarding statistics for a VPN instance
MPLS label forwarding for a VPN instance performs the following operations:
•Forwards a labeled packet for the VPN instance based on its incoming label.
•Adds a label to an unlabeled packet received by the VPN instance and forwards the labeled
packet.
Perform this task to enable MPLS label forwarding statistics for a VPN instance and MPLS statistics
reading. Then, you can use the display ip vpn-instance mpls statistics command to view MPLS
label statistics.
To enable MPLS label forwarding statistics:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter VPN instance view. ip vpn-instance vpn-instance-name N/A
3. Enable MPLS label
forwarding statistics for the
VPN instance. mpls statistics enable By default, MPLS label
forwarding statistics are disabled
for all VPN instances.
4. Enable MPLS label
statistics reading, and set
the reading interval. mpls statistics interval interval By default, MPLS label statistics
reading is disabled.
Enabling split horizon for MPLS forwarding
This feature prevents MPLS packets received from an interface from being forwarded back to that
interface to provide loop-free forwarding.
To enable split horizon for MPLS forwarding:
Step Command Remarks
1. Enter system view. system-view N/A