HPE FlexFabric 5950 Series User manual

HPE FlexFabric 5950 Switch Series
MPLS Configuration Guide
Part number: 5200-0827
Software version: Release 6106 and later
Document version: 6W100-20160513

© Copyright 2016 Hewlett Packard Enterprise Development LP
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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····························································································································································5
Protocols and standards ····························································································································5
MPLS configuration task list·······························································································································5
Enabling MPLS ··················································································································································6
Setting MPLS MTU ············································································································································6
Specifying the label type advertised by egress··································································································7
Configuring TTL propagation ·····························································································································8
Enabling sending MPLS TTL-expired messages·······························································································9
Enabling MPLS forwarding statistics··················································································································9
Enabling split horizon for MPLS forwarding·····································································································10
Enabling SNMP notifications for MPLS············································································································10
Displaying and maintaining MPLS ···················································································································10
Configuring a static LSP ···············································································12
Overview··························································································································································12
Configuration guidelines ··································································································································12
Configuration prerequisites······························································································································12
Configuration procedure ··································································································································13
Displaying static LSPs ·····································································································································13
Static LSP configuration example····················································································································13
Network requirements······························································································································13
Configuration restrictions and guidelines·································································································14
Configuration procedure···························································································································14
Verifying the configuration························································································································15
Configuring LDP····························································································17
Overview··························································································································································17
Terminology ·············································································································································17
LDP messages·········································································································································17
LDP operation··········································································································································18
Label distribution and control···················································································································19
LDP GR····················································································································································20
LDP-IGP synchronization·························································································································22
LDP over MPLS TE··································································································································23
Protocols··················································································································································23
LDP configuration task list ·······························································································································23
Enabling LDP···················································································································································24
Enabling LDP globally······························································································································24
Enabling LDP on an interface ··················································································································25
Configuring Hello parameters ··························································································································25
Configuring LDP session parameters ··············································································································26
Configuring LDP backoff··································································································································27
Configuring LDP MD5 authentication···············································································································28
Configuring LDP to redistribute BGP unicast routes························································································28
Configuring an LSP generation policy··············································································································29
Configuring the LDP label distribution control mode························································································30
Configuring a label advertisement policy ·········································································································30
Configuring a label acceptance policy ·············································································································31
Configuring LDP loop detection ·······················································································································32
Configuring LDP session protection·················································································································33
Configuring LDP GR ········································································································································33

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Configuring LDP-IGP synchronization ·············································································································33
Configuring LDP-OSPF synchronization··································································································34
Configuring LDP IS-IS synchronization····································································································35
Setting a DSCP value for outgoing LDP packets·····························································································35
Resetting LDP sessions···································································································································36
Enabling SNMP notifications for LDP ··············································································································36
Displaying and maintaining LDP······················································································································36
IPv4 LDP configuration examples····················································································································37
LDP LSP configuration example··············································································································37
Label acceptance control configuration example·····················································································41
Label advertisement control configuration example·················································································45
IPv6 LDP configuration examples····················································································································50
IPv6 LDP LSP configuration example······································································································50
IPv6 label acceptance control configuration example··············································································55
IPv6 label advertisement control configuration example··········································································60
Configuring MPLS TE···················································································66
Overview··························································································································································66
TE and MPLS TE·····································································································································66
MPLS TE basic concepts·························································································································66
Static CRLSP establishment····················································································································66
Dynamic CRLSP establishment···············································································································66
CRLSP establishment using PCE path calculation··················································································68
Traffic forwarding ·····································································································································69
Make-before-break···································································································································70
Route pinning···········································································································································71
Tunnel reoptimization·······························································································································71
CRLSP backup·········································································································································71
FRR··························································································································································71
DiffServ-aware TE····································································································································72
Bidirectional MPLS TE tunnel ··················································································································74
Protocols and standards ··························································································································75
MPLS TE configuration task list·······················································································································75
Enabling MPLS TE···········································································································································77
Configuring a tunnel interface··························································································································77
Configuring DS-TE···········································································································································78
Configuring an MPLS TE tunnel to use a static CRLSP ··················································································78
Configuring an MPLS TE tunnel to use a dynamic CRLSP·············································································79
Configuration task list·······························································································································79
Configuring MPLS TE attributes for a link································································································79
Advertising link TE attributes by using IGP TE extension········································································80
Configuring MPLS TE tunnel constraints·································································································81
Establishing an MPLS TE tunnel by using RSVP-TE···············································································83
Controlling CRLSP path selection············································································································83
Controlling MPLS TE tunnel setup···········································································································85
Configuring an MPLS TE tunnel to use a CRLSP calculated by PCEs ···························································87
Configuring a PCE ···································································································································87
Discovering PCEs····································································································································87
Establishing a CRLSP by using the path calculated by PCEs·································································87
Establishing a backup CRLSP by using the path calculated by PCEs·····················································88
Configuring PCEP session parameters····································································································88
Configuring traffic forwarding···························································································································89
Configuring static routing to direct traffic to an MPLS TE tunnel······························································89
Configuring automatic route advertisement to direct traffic to an MPLS TE tunnel··································89
Configuring a bidirectional MPLS TE tunnel ····································································································90
Configuring CRLSP backup·····························································································································91
Configuring MPLS TE FRR······························································································································91
Enabling FRR···········································································································································91
Configuring a bypass tunnel on the PLR··································································································92
Configuring node fault detection ··············································································································96
Setting the optimal bypass tunnel selection interval ················································································96
Enabling SNMP notifications for MPLS TE······································································································96

iii
Displaying and maintaining MPLS TE··············································································································97
MPLS TE configuration examples····················································································································98
Establishing an MPLS TE tunnel over a static CRLSP············································································98
Establishing an MPLS TE tunnel with RSVP-TE····················································································102
Establishing an inter-AS MPLS TE tunnel with RSVP-TE······································································108
Establishing an inter-area MPLS TE tunnel over a CRLSP calculated by PCEs···································115
Bidirectional MPLS TE tunnel configuration example············································································120
CRLSP backup configuration example ··································································································126
Manual bypass tunnel for FRR configuration example ··········································································130
Auto FRR configuration example···········································································································135
IETF DS-TE configuration example ·······································································································141
Troubleshooting MPLS TE·····························································································································148
No TE LSA generated····························································································································148
Configuring a static CRLSP········································································150
Overview························································································································································150
Configuration procedure ································································································································150
Displaying static CRLSPs ······························································································································151
Static CRLSP configuration example·············································································································151
Network requirements····························································································································151
Configuration procedure·························································································································152
Verifying the configuration······················································································································154
Configuring RSVP·······················································································157
Overview························································································································································157
RSVP messages····································································································································157
CRLSP setup procedure························································································································158
RSVP refresh mechanism······················································································································158
RSVP authentication······························································································································159
RSVP GR···············································································································································159
Protocols and standards ························································································································160
RSVP configuration task list···························································································································160
Enabling RSVP··············································································································································160
Configuring RSVP refresh······························································································································160
Configuring RSVP Srefresh and reliable RSVP message delivery································································161
Configuring RSVP hello extension·················································································································161
Configuring RSVP authentication ··················································································································162
Setting a DSCP value for outgoing RSVP packets························································································163
Configuring RSVP GR ···································································································································164
Enabling BFD for RSVP·································································································································164
Displaying and maintaining RSVP ·················································································································164
RSVP configuration examples ·······················································································································165
Establishing an MPLS TE tunnel with RSVP-TE····················································································165
RSVP GR configuration example···········································································································171
Configuring tunnel policies··········································································174
Overview························································································································································174
Configuring a tunnel policy·····························································································································174
Configuration guidelines·························································································································174
Configuration procedure·························································································································175
Displaying tunnel information·························································································································175
Tunnel policy configuration examples············································································································176
Exclusive tunnel configuration example·································································································176
Preferred tunnel and tunnel selection order configuration example·······················································176
Configuring MPLS L3VPN ··········································································179
Overview························································································································································179
Basic MPLS L3VPN architecture ···········································································································179
MPLS L3VPN concepts··························································································································179
MPLS L3VPN route advertisement········································································································181
MPLS L3VPN packet forwarding············································································································182
MPLS L3VPN networking schemes·······································································································183

iv
Inter-AS VPN··········································································································································185
Carrier's carrier ······································································································································189
Nested VPN ···········································································································································191
HoVPN···················································································································································192
OSPF VPN extension·····························································································································194
BGP AS number substitution and SoO attribute····················································································196
MPLS L3VPN FRR·································································································································197
Protocols and standards ························································································································199
MPLS L3VPN configuration task list ··············································································································199
Configuring basic MPLS L3VPN····················································································································200
Configuration prerequisites····················································································································200
Configuring VPN instances····················································································································200
Configuring routing between a PE and a CE ·························································································202
Configuring routing between PEs···········································································································207
Configuring BGP VPNv4 route control···································································································207
Configuring inter-AS VPN ······························································································································209
Configuring inter-AS option A·················································································································209
Configuring inter-AS option B·················································································································209
Configuring inter-AS option C ················································································································210
Configuring nested VPN ································································································································213
Configuring HoVPN········································································································································214
Configuring an OSPF sham link·····················································································································215
Configuring a loopback interface············································································································215
Redistributing the loopback interface address·······················································································216
Creating a sham link ······························································································································216
Specifying the VPN label processing mode on the egress PE ······································································216
Configuring BGP AS number substitution and SoO attribute·········································································217
Configuring MPLS L3VPN FRR·····················································································································217
Enabling SNMP notifications for MPLS L3VPN ·····························································································219
Enabling logging for BGP route flapping········································································································220
Displaying and maintaining MPLS L3VPN·····································································································220
MPLS L3VPN configuration examples···········································································································221
Configuring basic MPLS L3VPN············································································································221
Configuring a hub-spoke network ··········································································································227
Configuring MPLS L3VPN inter-AS option A ·························································································233
Configuring MPLS L3VPN inter-AS option B ·························································································238
Configuring MPLS L3VPN inter-AS option C·························································································243
Configuring MPLS L3VPN carrier's carrier in the same AS ···································································250
Configuring MPLS L3VPN carrier's carrier in different ASs ···································································258
Configuring nested VPN·························································································································265
Configuring HoVPN································································································································274
Configuring an OSPF sham link·············································································································281
Configuring BGP AS number substitution······························································································286
Configuring BGP AS number substitution and SoO attribute·································································289
Configuring MPLS L3VPN FRR through VPNv4 route backup for a VPNv4 route ································292
Configuring MPLS L3VPN FRR through VPNv4 route backup for an IPv4 route ··································294
Configuring MPLS L3VPN FRR through IPv4 route backup for a VPNv4 route ····································296
Configuring IPv6 MPLS L3VPN ··································································299
Overview························································································································································299
IPv6 MPLS L3VPN packet forwarding ···································································································299
IPv6 MPLS L3VPN routing information advertisement ··········································································300
IPv6 MPLS L3VPN network schemes and features···············································································300
Protocols and standards ························································································································300
IPv6 MPLS L3VPN configuration task list······································································································301
Configuring basic IPv6 MPLS L3VPN············································································································301
Configuration prerequisites····················································································································301
Configuring VPN instances····················································································································301
Configuring routing between a PE and a CE ·························································································303
Configuring routing between PEs···········································································································309
Configuring BGP VPNv6 route control···································································································309
Configuring inter-AS IPv6 VPN······················································································································311

v
Configuring inter-AS IPv6 VPN option A································································································311
Configuring inter-AS IPv6 VPN option C································································································312
Configuring an OSPFv3 sham link·················································································································313
Configuring a loopback interface············································································································313
Redistributing the loopback interface address·······················································································313
Creating a sham link ······························································································································314
Configuring BGP AS number substitution and SoO attribute·········································································314
Enabling logging for BGP route flapping········································································································315
Displaying and maintaining IPv6 MPLS L3VPN·····························································································315
IPv6 MPLS L3VPN configuration examples···································································································316
Configuring IPv6 MPLS L3VPNs············································································································316
Configuring a hub-spoke network ··········································································································322
Configuring IPv6 MPLS L3VPN inter-AS option A·················································································329
Configuring IPv6 MPLS L3VPN inter-AS option C·················································································334
Configuring IPv6 MPLS L3VPN carrier's carrier in the same AS···························································340
Configuring an OSPFv3 sham link·········································································································347
Configuring BGP AS number substitution······························································································352
Configuring BGP AS number substitution and SoO attribute·································································356
Configuring MPLS OAM··············································································359
Overview························································································································································359
MPLS ping··············································································································································359
MPLS tracert··········································································································································359
BFD for MPLS········································································································································359
Periodic MPLS tracert····························································································································360
Protocols and standards ································································································································360
Configuring MPLS OAM for LSP tunnels·······································································································360
Configuring MPLS ping for LSPs ···········································································································360
Configuring MPLS tracert for LSPs········································································································360
Configuring BFD for LSPs······················································································································361
Configuring periodic MPLS tracert for LSPs ··························································································362
Configuring MPLS OAM for MPLS TE tunnels ······························································································362
Configuring MPLS ping for MPLS TE tunnels························································································362
Configuring MPLS tracert for MPLS TE tunnels·····················································································362
Configuring BFD for MPLS TE tunnels ··································································································363
Displaying MPLS OAM ··································································································································363
BFD for LSP configuration example···············································································································364
Network requirements····························································································································364
Configuration procedure·························································································································364
Verifying the configuration······················································································································365
Configuring MCE·························································································367
MPLS L3VPN overview··································································································································367
Basic MPLS L3VPN architecture ···········································································································367
MPLS L3VPN concepts··························································································································367
MCE overview················································································································································369
MCE configuration task list ····························································································································618H370
280HConfiguring VPN instances····························································································································619H370
281HCreating a VPN instance························································································································620H371
282HAssociating a VPN instance with an interface························································································621H371
283HConfiguring route related attributes for a VPN instance·········································································622H371
284HConfiguring routing on an MCE······················································································································623H372
285HConfiguring routing between an MCE and a VPN site···········································································624H373
286HConfiguring routing between an MCE and a PE ····················································································625H377
287HDisplaying and maintaining MCE···················································································································626H380
288HMCE configuration examples·························································································································627H380
289HConfiguring the MCE that uses OSPF to advertise VPN routes to the PE·············································628H380
290HConfiguring the MCE that uses EBGP to advertise VPN routes to the PE ············································629H385
291HConfiguring IPv6 MCE ················································································630H390
292HIPv6 MPLS L3VPN overview ·························································································································631H390
293HIPv6 MCE overview········································································································································632H390

vi
IPv6 MCE configuration task list ····················································································································390
295HConfiguring VPN instances····························································································································634H391
296HCreating a VPN instance························································································································635H391
297HAssociating a VPN instance with an interface························································································636H391
298HConfiguring route related attributes for a VPN instance·········································································637H392
299HConfiguring routing on an MCE······················································································································638H393
300HConfiguring routing between an MCE and a VPN site···········································································639H393
301HConfiguring routing between an MCE and a PE ····················································································640H397
302HDisplaying and maintaining IPv6 MCE···········································································································641H400
303HIPv6 MCE configuration example···················································································································642H400
304HNetwork requirements····························································································································643H400
305HConfiguration procedure·························································································································644H401
306HVerifying the configuration······················································································································645H405
307HDocument conventions and icons·······························································646H407
308HConventions···················································································································································647H407
309HNetwork topology icons··································································································································648H408
310HSupport and other resources ······································································649H409
311HAccessing Hewlett Packard Enterprise Support ····························································································650H409
312HAccessing updates·········································································································································651H409
313HWebsites ················································································································································652H410
314HCustomer self repair·······························································································································653H410
315HRemote support······································································································································654H410
316HDocumentation feedback ·······················································································································655H410
317HIndex···········································································································656H412

1
0BConfiguring 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.
14BOverview
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.
136BBasic concepts
317BFEC
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.
318BLabel
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.
319BLSR
A router that performs MPLS forwarding is a label switching router (LSR).

2
320BLSP
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 657HFigure 2, LSR B is the
downstream LSR of LSRA, and LSR A is the upstream LSR of LSR B.
Figure 2 Label switched path
321BLFIB
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.
322BControl 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.
137BMPLS 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.
•Egress LSR—Egress LSR of packets. It removes labels from packets and forwards the
packets to their destination networks.

3
Figure 3 MPLS network architecture
138BLSP 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.

4
Figure 4 Dynamic LSP establishment
139BMPLS forwarding
As shown in 658HFigure 5, a packet is forwarded over the MPLS network as follows:
1. Device 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 VLAN-interface 2 to the next hop LSR
Device C.
2. When receiving the labeled packet, Device 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 VLAN-interface 3 to the next hop
LSR Device D.
3. When receiving the labeled packet, Device 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 VLAN-interface 4 to the next hop LSR
Device E.
If the LFIB entry records no outgoing interface or next hop information, Device D performs the
following operations:
a. Identifies the FIB entry by the IP header.
b. Forwards the packet according to the FIB entry.

5
Figure 5 MPLS forwarding
140BPHP
An egress node must perform two forwarding table lookups to forward a packet:
•Two LFIB lookups (if the packet has more than one label).
•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.
141BProtocols 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
15BMPLS configuration task list
Tasks at a glance
(Required.) 659HEnabling MPLS

6
Tasks at a glance
(Optional.) 660HSetting MPLS MTU
(Optional.) 661HSpecifying the label type advertised by egress
(Optional.) 662HConfiguring TTL propagation
(Optional.) 663HEnabling sending MPLS TTL-expired messages
(Optional.) 664HEnabling MPLS forwarding statistics
(Optional.) 665HEnabling split horizon for MPLS forwarding
(Optional.) 666HEnabling SNMP notifications for MPLS
16BEnabling 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.
17BSetting 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.

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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 size By default, no MPLS MTU is set
on an interface.
The following applies when an interface handles MPLS packets:
•MPLS packets carrying 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.
18BSpecifying the label type advertised by egress
In an MPLS network, an egress node 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. The value range for a non-null label is 16 to 1048575.
For LSPs established by a label distribution protocol, the label advertised by the egress node
determines how the penultimate hop processes a labeled packet.
•If the egress node advertises an implicit null label, the penultimate hop directly pops the top
label of a matching packet.
•If the egress node 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 node advertises a non-null label, the penultimate hop swaps the top label of a
matching packet with the label assigned by the egress node.
323BConfiguration guidelines
As a best practice, configure the egress node to advertise an implicit null label to the penultimate hop
if the penultimate hop supports PHP. If you want to simplify packet forwarding on egress but keep
labels to determine QoS policies, configure the egress node 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 node, the egress node 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 node.
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.

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324BConfiguration 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
node to the penultimate hop.
mpls label advertise
{ explicit-null | implicit-null |
non-null }
By default, an egress node
advertises an implicit null label to
the penultimate hop.
19BConfiguring TTL propagation
When TTLpropagation is enabled, the ingress node copies the TTLvalue 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:

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•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
2. Enable TTL
propagation. mpls ttl propagate { public |
vpn }
By default, TTL propagation is enabled for
public network packets and is disabled for
VPN 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.
20BEnabling sending 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 node, which then sends the message back to the source.
To enable sending MPLS TTL-expired messages:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable sending MPLS
TTL-expired messages. mpls ttl expiration enable By default, this feature is enabled.
21BEnabling MPLS forwarding statistics
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 set the statistics collection
interval. Then, you can use the display mpls lsp verbose command to view MPLS label statistics.
If you execute the mpls statistics enable command for a VPN instance, MPLS label forwarding
statistics is enabled for all LSPs in that VPN instance. For more information about enabling MPLS
label forwarding statistics for a VPN instance, see "667HConfiguring MPLS L3VPN."
To enable MPLS label forwarding statistics for LSPs:
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-address mask-length | ipv6
ipv6-address prefix-length } | static |
te ingress-lsr-id tunnel-id }
By default, MPLS label
forwarding statistics is disabled
for all LSPs.
3. Set the MPLS label
forwarding statistics
collection interval. mpls statistics interval interval By default, the MPLS label
forwarding statistics collection
interval is not set.

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22BEnabling 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
2. Enable split horizon for
MPLS forwarding. mpls forwarding split-horizon By default, split horizon is
disabled for MPLS forwarding.
23BEnabling SNMP notifications for MPLS
To report critical MPLS events to an NMS, enable SNMP notifications for MPLS. For MPLS event
notifications to be sent correctly, you must also configure SNMPon the device. For more information
about SNMP configuration, see the network management and monitoring configuration guide for the
device.
To enable SNMP notifications for MPLS:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enable SNMP
notifications for MPLS. snmp-agent trap enable mpls By default, SNMP notifications for
MPLS are enabled.
24BDisplaying and maintaining MPLS
Execute display commands in any view and reset commands in user view.
Task Command
Display MPLS interface information. display mpls interface [ interface-type
interface-number ]
Display usage information for MPLS labels. display mpls label { label-value1 [ to label-value2 ] | all }
Display LSP information.
display mpls lsp [ egress | in-label label-value | ingress
| outgoing-interface interface-type interface-number |
protocol { bgp | ldp | local | rsvp-te | static | static-cr } |
transit ] [ vpn-instance vpn-instance-name ]
[ ipv4-address mask-length | ipv6 [ ipv6-address
prefix-length ] ] [ verbose ]
Display MPLS Nexthop Information Base (NIB)
information. display mpls nib [ nib-id ]
Display usage information for NIDs. display mpls nid [ nid-value1 [ to nid-value2 ] ]
Display LSP statistics. display mpls lsp statistics [ ipv6 ]
Display MPLS summary information. display mpls summary
Display ILM entries. display mpls forwarding ilm [ label ] [ slot slot-number ]

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Task Command
Display NHLFE entries. display mpls forwarding nhlfe [ nid ] [ slot slot-number ]
Clear MPLS forwarding statistics for the
specified LSPs.
reset mpls statistics { all | [ vpn-instance
vpn-instance-name ] { ipv4 ipv4-address mask-length |
ipv6 ipv6-address prefix-length } | static | te ingress-lsr-id
tunnel-id }

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1BConfiguring a static LSP
25BOverview
A static label switched path (LSP) is established by manually specifying the incoming label and
outgoing label on each node (ingress, transit, or egress node) of the forwarding path.
Static LSPs consume fewer resources, but they cannot automatically adapt to network topology
changes. Therefore, static LSPs are suitable for small and stable networks with simple topologies.
The ingress node of a static LSP performs the following operations:
1. Determines an FEC for a packet according to the destination address.
2. Adds the label for that FEC into the packet.
3. Forwards the packet to the next hop or out of the outgoing interface.
A transit node swaps the label carried in a received packet with a label, and forwards the packet to
the next hop or out of the outgoing interface.
If PHP is not configured, an egress node pops the incoming label of a packet, and performs label
forwarding according to the inner label or IP forwarding.
26BConfiguration guidelines
Follow these guidelines when you establish a static LSP:
•On the ingress node, you must specify the outgoing label for the destination address (the FEC)
and the next hop or the outgoing interface.
•On each transit node, you must specify the incoming label, the outgoing label, and the next hop
or the outgoing interface.
•On the egress node, you must specify the incoming label.
•You can associate a static LSP with an LDP LSP to simplify packet processing when the
following conditions are met:
{Packets are forwarded over the static LSP and the LDP LSP to the destination.
{The egress node of the static LSP is also the ingress node of the LDP LSP.
After receiving a packet with the specified incoming label, the egress node of the static LSP
swaps the label with the outgoing label for the LDP LSP. Then, the node forwards the packet to
the next hop.
To associate a static LSP with an LDP LSP, specify the incoming label and destination address
on the egress node of the static LSP.
•The outgoing label specified on an LSR must be the same as the incoming label specified on
the directly connected downstream LSR.
27BConfiguration prerequisites
Before you configure a static LSP, perform the following tasks:
•Identify the ingress node, transit nodes, and egress node of the LSP.
•Enable MPLS on all interfaces that participate in MPLS forwarding. For more information, see
"668HConfiguring basic MPLS."
•Make sure the ingress node has a route to the destination address of the LSP.