H3C S12500 Series User manual

H3C S12500 Series Routing Switches
SPB Configuration Guide
Hangzhou H3C Technologies Co., Ltd.
http://www.h3c.com
Software version: S12500-CMW730-R7374
Document version: 6W731-20150528

Copyright © 2014-2015, Hangzhou H3C Technologies Co., Ltd. and its licensors
All rights reserved
No part of this manual may be reproduced or transmitted in any form or by any means without prior
written consent of Hangzhou H3C Technologies Co., Ltd.
Trademarks
H3C, , H3CS, H3CIE, H3CNE, Aolynk, , H3Care, , IRF, NetPilot, Netflow,
SecEngine, SecPath, SecCenter, SecBlade, Comware, ITCMM and HUASAN are trademarks of
Hangzhou H3C Technologies Co., Ltd.
All other trademarks that may be mentioned in this manual are the property of their respective owners
Notice
The information in this document is subject to change without notice. Every effort has been made in the
preparation of this document to ensure accuracy of the contents, but all statements, information, and
recommendations in this document do not constitute the warranty of any kind, express or implied.

Preface
The H3C S12500 documentation set includes 17 configuration guides. These guides describe the
software features for the H3C S12500 Series 10G Core Routing Switches and guide you through the
software configuration procedures. These guides also provide configuration examples to help you apply
software features to different network scenarios.
The SPB Configuration Guide describes Shortest Path Bridging MAC Mode (SPBM) fundamentals and
configuration. SPBM enables multipath routing in an Ethernet mesh network by using IS-IS as the control
protocol. The technology allows all paths to be active, supports equal cost paths, and provides shortest
path forwarding in an Ethernet mesh network. SPBM provides faster convergence, higher link efficiency,
and larger Layer 2 topologies than conventional spanning tree protocols such as MSTP.
This preface includes:
•Audience
•Conventions
•About the H3C S12500 documentation set
•Obtaining documentation
•Technical support
•Documentation feedback
Audience
This documentation is intended for:
•Network planners
•Field technical support and servicing engineers
•Network administrators working with the S12500 series
Conventions
This section describes the conventions used in this documentation set.
Command conventions
Convention Descri
p
tion
Boldface Bold text represents commands and keywords that you enter literally as shown.
Italic Italic text represents arguments that you replace with actual values.
[ ] Square brackets enclose syntax choices (keywords or arguments) that are optional.
{ x | y | ... }
Braces enclose a set of required syntax choices separated by vertical bars, from which
you select one.
[ x | y | ... ]
Square brackets enclose a set of optional syntax choices separated by vertical bars, from
which you select one or none.

Convention Descri
p
tion
{ x | y | ... } *
Asterisk marked braces enclose a set of required syntax choices separated by vertical
bars, from which you select at least one.
[ x | y | ... ] *
Asterisk marked square brackets enclose optional syntax choices separated by vertical
bars, from which you select one choice, multiple choices, or none.
&<1-n> The argument or keyword and argument combination before the ampersand (&) sign can
be entered 1 to n times.
# A line that starts with a pound (#) sign is comments.
GUI conventions
Convention Descri
p
tion
Boldface Window names, button names, field names, and menu items are in Boldface. For
example, the New User window appears; click OK.
> Multi-level menus are separated by angle brackets. For example, File > Create > Folder.
Symbols
Convention Descri
p
tion
WARNING An alert that calls attention to important information that if not understood or followed can
result in personal injury.
CAUTION An alert that calls attention to important information that if not understood or followed can
result in data loss, data corruption, or damage to hardware or software.
IMPORTANT An alert that calls attention to essential information.
NOTE An alert that contains additional or supplementary information.
TIP An alert that provides helpful information.
Network topology icons
Represents a generic network device, such as a router, switch, or firewall.
Represents a routing-capable device, such as a router or Layer 3 switch.
Represents a generic switch, such as a Layer 2 or Layer 3 switch, or a router that supports
Layer 2 forwarding and other Layer 2 features.
Represents an access controller, a unified wired-WLAN module, or the access controller
engine on a unified wired-WLAN switch.
Represents an access point.
Represents a mesh access point.


Represents omnidirectional signals.
Represents directional signals.
Represents a security product, such as a firewall, UTM, multiservice security gateway, or
load-balancing device.
Represents a security card, such as a firewall, load-balancing, NetStream, SSL VPN, IPS,
or ACG card.
Port numbering in examples
The port numbers in this document are for illustration only and might be unavailable on your device.
About the H3C S12500 documentation set
The H3C S12500 documentation set includes:
Cate
g
or
y
Documents Pur
p
oses
Product description and
specifications
Marketing brochures Describe product specifications and benefits.
Technology white papers
Provide an in-depth description of software features
and technologies.
Card datasheets Describe card specifications, features, and
standards.
Hardware specifications
and installation
Regulatory compliance
and safety information
Provides regulatory information and the safety
instructions that must be followed during installation.
Installation guide Provides a complete guide to hardware installation
and hardware specifications.
Quick start
Guides you through initial installation and setup
procedures to help you quickly set up and use your
switch with the minimum configuration.
H3C Pluggable SFP
[SFP+][XFP] Transceiver
Modules Installation
Guide
Guides you through installing SFP/SFP+/XFP
transceiver modules.
H3C QSFP+ Transceiver
Modules[Cables]
Installation Guide
Guides you through installing QSFP+ transceiver
modules.
H3C CFP Transceiver
Modules Installation
Guide
Guides you through installing CFP transceiver
modules.
Adjustable Slider Rail
Installation Guide
Guides you through installing adjustable slider rails
to a rack.
H3C High-End Network
Products Hot-Swappable
Module Manual
Describes the hot-swappable modules available for
the H3C high-end network products, their external
views, and specifications.




Cate
g
or
y
Documents Pur
p
oses
Software configuration
Configuration guides Describe software features and configuration
procedures.
Command references Provide a quick reference to all available
commands.
Operations and
maintenance
System log messages Explains the system log messages.
Trap messages Explains the trap messages.
MIB Companion Describes the MIBs for the software release.
Release notes
Provide information about the product release,
including the version history, hardware and software
compatibility matrix, version upgrade information,
technical support information, and software
upgrading.
Obtaining documentation
Access the most up-to-date H3C product documentation on the World Wide Web
at http://www.h3c.com.
Click the links on the top navigation bar to obtain different categories of product documentation:
[Technical Support & Documents > Technical Documents]—Provides hardware installation, software
upgrading, and software feature configuration and maintenance documentation.
[Products & Solutions]—Provides information about products and technologies, as well as solutions.
[Technical Support & Documents > Software Download]—Provides the documentation released with the
software version.
Technical support
servic[email protected]
http://www.h3c.com
Documentation feedback
You can e-mail your comments about product documentation to [email protected].
We appreciate your comments.

i
Contents
SPBM overview ···························································································································································· 1
SPBM network model························································································································································1
Terminology ·······································································································································································1
Area···········································································································································································1
BCB ············································································································································································2
BEB·············································································································································································2
B-MAC, B-VLAN························································································································································2
Customer network port, provider network port ·····································································································2
Ethernet service instance··········································································································································2
I-SID············································································································································································2
ISIS-SPB······································································································································································2
LSDB···········································································································································································3
MAC-in-MAC ····························································································································································3
PW ·············································································································································································3
SPB VSI ······································································································································································3
SPBM packet types····························································································································································3
ISIS-SPB control packets···········································································································································3
SPBM data packet····················································································································································4
Working mechanisms ·······················································································································································4
Formation and maintenance of ISIS-SPB adjacencies ··························································································5
MAC address learning ············································································································································5
Data paths·································································································································································5
SPBM multicast address···········································································································································8
Multiple SPB VSIs ······························································································································································9
Load balancing ······························································································································································ 10
B-VLAN to ECT algorithm mapping····················································································································· 10
ECT migration ························································································································································ 11
Loop prevention······························································································································································ 12
Multicast B-VLAN···························································································································································· 12
Fast channel for quick spread of LSPs·························································································································· 12
Protocols and standards ················································································································································ 12
Configuring SPBM······················································································································································13
Configuration restrictions and guidelines···················································································································· 13
Hardware restrictions············································································································································ 13
Feature compatibility requirements······················································································································ 14
Licensing requirements·········································································································································· 15
SPBM configuration task list·········································································································································· 15
Configuring basic SPBM settings on BEBs and BCBs································································································· 16
Configuring MST region parameters··················································································································· 16
Enabling SPBM ······················································································································································ 17
Configuring customer-side settings on BEBs ················································································································ 17
Enabling L2VPN ···················································································································································· 17
Creating an SPB VSI ············································································································································· 18
Assigning a B-VLAN to an SPB VSI ····················································································································· 18
Configuring Ethernet service instances on BEBs································································································· 18
Configuring the SPBM multicast replication mode on BEBs·············································································· 19
Enabling the multicast B-VLAN feature························································································································· 20
Optimizing the SPBM network······································································································································ 20

ii
Configuring the SPSource ID································································································································ 21
Configuring the bridge priority···························································································································· 21
Configuring a link metric value for a provider network port············································································ 21
Mapping B-VLANs to an ECT algorithm ············································································································· 22
Performing ECT migration for an SPB VSI ·········································································································· 23
Enabling dynamic hostname exchange ·············································································································· 24
Configuring Graceful Restart for ISIS-SPB··········································································································· 25
Tuning ISIS-SPB adjacency maintenance settings ······························································································ 25
Tuning ISIS-SPB LSP timers ···································································································································· 26
Tuning the SPF calculation timer ·························································································································· 29
Setting the LSDB overload bit······························································································································· 30
Enabling outputting ISIS-SPB adjacency changes to the configuration terminal············································· 30
Configuring the group MAC address for ISIS-SPB····························································································· 30
Configuring ISIS-SPB authentication ···················································································································· 31
Configuring SNMP notifications and context for SPBM···················································································· 32
Configuring the AP mode·············································································································································· 33
Displaying and maintaining SPBM ······························································································································ 33
SPBM configuration examples······································································································································ 36
SPBM with head-end replication configuration example ·················································································· 36
SPBM with tandem replication configuration example ····················································································· 39
ECT migration example ········································································································································ 42
Index ···········································································································································································46

1
SPBM overview
IEEE 802.1aq Shortest Path Bridging (SPB) enables multipath routing in an Ethernet mesh network by
using IS-IS as the control protocol. The technology allows all paths to be active, supports equal cost paths,
and provides shortest path forwarding in an Ethernet mesh network. IEEE 802.1aq SPB provides faster
convergence, higher link efficiency, and larger Layer 2 topologies than conventional spanning tree
protocols such as MSTP.
Shortest path bridging MAC mode (SPBM) is one bridging method of IEEE 802.1aq SPB. This method
encapsulates Ethernet frames into MAC-in-MAC frames in compliance with IEEE 802.1ah PBB.
SPBM network model
As shown in Figure 1, the SPBM network includes backbone edge bridges and backbone core bridges.
Backbone edge bridges connect customer sites to the SPBM network.
The nodes in the SPBM network run ISIS-SPB to prevent loops and calculate the shortest path for a frame.
Figure 1 SPBM network model
Terminology
Area
An SPBM area is a subdomain of an SPBM network. The device supports only one area.
Customer
site Customer site
Customer
site
Customer
site
SPBM
network
BCB BCB
BCBBCB
BEB BEB
BEB BEB

2
BCB
Backbone core bridges (BCBs) are core nodes of an SPBM network. They are identical to the P devices
in an MPLS VPN network. BCBs forward MAC-in-MAC frames based on the B-MAC and B-VLAN. They
do not learn customer MAC (C-MAC) addresses.
BEB
Backbone edge bridges (BEBs) are edge nodes of the SPBM network. They are identical to PEs in an
MPLS VPN network. BEBs encapsulate customer frames into MAC-in-MAC frames before forwarding
them to the SPBM network. BEBs also decapsulate MAC-in-MAC frames before sending them to a
customer site.
B-MAC, B-VLAN
Backbone MAC addresses (B-MACs) are bridge MAC addresses associated with SPBM bridges.
Backbone VLANs (B-VLANs) are VLANs assigned by the service provider for transmitting customer traffic
on the SPBM network.
For customer frames to be transmitted across an SPBM network, the ingress BEB encapsulates them in
MAC-in-MAC format. In the outer frame header, the source MAC address is a B-MAC of the ingress BEB,
and the destination MAC is a B-MAC of the egress BEB. All devices in the SPBM network forward the
MAC-in-MAC frames based on the destination B-MAC and B-VLAN.
Customer network port, provider network port
On a BEB, a customer network port (CNP) connects to a customer site and a provider network port (PNP)
connects to the SPBM network.
Ethernet service instance
An Ethernet service instance provides forwarding service for a set of C-VLANs. To extend C-VLANs across
customer sites over an SPBM network, you must configure Ethernet service instances on BEBs' customer
edge ports and map them to SPB VSIs.
For more information about Ethernet service instances, see VPLS in MPLS Configuration Guide.
I-SID
A backbone services instance identifier (I-SID) uniquely identifies a MAC-in-MAC service instance (also
called an "SPB VSI") provided by the service provider.
ISIS-SPB
ISIS-SPB is the control protocol for an SPBM network to calculate shortest path trees (SPTs) and maintain
adjacencies between neighbors.

3
LSDB
A link state database (LSDB) contains the states of all links in an SPBM network.
MAC-in-MAC
SPBM encapsulates Ethernet frames into MAC-in-MAC frames by using 802.1ah PBB encapsulation. For
more information about the MAC-in-MAC frame format, see "Data paths."
Customer frames are encapsulated in MAC-in-MAC format at edges of the SPBM network before they are
forwarded from one customer site to another.
PW
Pseudo wires (PWs) are MAC-in-MAC tunnels established over the SPBM network for transmitting
customer traffic.
PWs are established between BEBs. BCBs do not set up PWs.
SPB VSI
An SPB virtual service instance (SPB VSI) provides MAC-in-MAC tunnel service for Ethernet service
instances. Each SPB VSI is uniquely identified by an I-SID. For more information about VSIs, see VPLS in
MPLS Configuration Guide.
SPBM packet types
SPBM packets include ISIS-SPB control packets and SPBM data packets.
ISIS-SPB control packets
ISIS-SPB control packets include hello, LSP, and SNP. All SPBM control packets are encapsulated in
802.1q.
Hello
SPBM neighbors send IS-IS hello (IIH) PDUs to establish and maintain adjacencies.
LSP
Adjacent SPBM neighbors send link state PDUs (LSPs) to advertise topology data.
SNP
Adjacent SPBM neighbors exchange sequence number PDUs (SNPs) for LSDB synchronization.
SNPs include complete SNP (CSNP) and partial SNP (PSNP).
•CSNP—Contains the digest of each LSP in the LSDB. Adjacent routers exchange CSNPs to maintain
LSDB synchronization.
•PSNP—Contains the sequence numbers of recently received LSPs. An SPBM node uses a PSNP to
acknowledge LSPs or to request needed LSPs from a neighbor.

4
SPBM data packet
SPBM data packets use the IEEE 802.1ah MAC-in-MAC frame format, as shown in Figure 2.
Figure 2 IEEE 802.1ah-compliant MAC-in-MAC frame format
Table 1 IEEE 802.1ah encapsulated frame header fields
Field Description
B-DA Destination B-MAC that identifies the destination BEB.
B-SA Source B-MAC. It is a known MAC address of the BEB that encapsulates the MAC-in-MAC
frame.
B-Tag B-VLAN tag identifies the VLAN ID and priority of the frame in the SPBM network. The TPID
in the tag is fixed at 0x8100.
I-Tag
Backbone service instance tag contains the following subfields:
•TPID—A value fixed at 0x88E7 to identify the frame as an 802.1ah encapsulated frame.
•I-PCP—Transmission priority of the frame on the BEB.
•I-DEI—Drop priority of the frame on the BEB.
•I-SID—Backbone service instance identifier.
•C-DA—Customer destination MAC address.
•C-SA—Customer source MAC address.
S-Tag This field contains the outer customer VLAN ID and priority.
C-Tag This field contains the inner customer VLAN ID and priority.
Working mechanisms
To forward Layer 2 traffic between customer sites across an SPBM network, you must configure Ethernet
service instances on BEBs' customer network ports, and map Ethernet service instances to SPB VSIs.
SPBM uses ISIS-SPB in the control plane to calculate shortest path trees. It uses IEEE 802.1ah PBB
encapsulation in the data plane to encapsulate and forward traffic.
SPBM uses the following generic process to calculate SPTs and forward traffic:
1. BEBs and BCBs send ISIS-SPB P2P hellos to establish and maintain adjacencies.
2. Adjacent nodes send LSPs to advertise their respective topology data. Eventually, the LSDBs of all
nodes are synchronized.
3. Each node selects the forwarding path:

5
a. Each node runs SPF to calculate the shortest path from itself to each of the other nodes.
b. If equal-cost paths are available, each node runs ECT to choose the best forwarding path.
c. The nodes populate their respective FDB and FIB tables with the forwarding path.
4. BEBs establish PWs over the SPBM network for transmitting customer traffic.
Formation and maintenance of ISIS-SPB adjacencies
ISIS-SPB only supports point-to-point links within an IS-IS level 1. It sends P2P hellos between directly
connected nodes to form and maintain adjacencies. To forward traffic on an adjacency, two SPBM
neighbors must meet the following requirements:
•The neighbors have the same configuration digest for MSTI 4092.
•The neighbors have the same B-VLAN to ECT algorithm mapping.
•The neighbors have valid link metric values.
MAC address learning
In an SPBM network, BEBs perform typical source MAC learning in the data plane to learn C-MACs, but
BCBs do not learn C-MACs.
BCBs forward MAC-in-MAC traffic by destination B-MAC and B-VLAN, which are advertised through
ISIS-SPB in the control plane. As a result, BCBs do not need to maintain a large MAC address table.
Data paths
For the forwarding process for known unicast frames, see "Unicast."
To avoid loops, SPBM does not support broadcast. BEBs flood broadcast, unknown unicast, and
unknown multicast frames to the SPBM network as multicast frames. For the flooding process, see
"Multicast."
Unicast
For an intra-site known unicast frame, the ingress BEB performs typical MAC address table lookup.
For a known inter-site unicast frame, the following forwarding process takes place, as shown in Figure 3:
1. The ingress BEB performs the following tasks:
a. Assigns the frame to the correct Ethernet service instance based on the outer VLAN.
b. Learns the source MAC address.
c. Looks up the destination MAC address in the Ethernet service instance's Ethernet address table.
2. If the outgoing interface is a provider network port, the ingress BEB performs the following tasks:
a. Encapsulates the frame in IEEE 802.1ah format.
b. Sends the frame out of the unicast PW to the egress BEB.
The B-DA field in the outer frame header is the B-MAC of the egress BEB.
3. Each BCB on the unicast PW forwards the frame based on the B-MAC and B-VLAN in the outer
frame header until it reaches the egress BEB.
4. The egress BEB removes the outer frame header and forwards the frame to the destination
customer MAC address.

6
Figure 3 MAC-in-MAC unicast traffic over an SPBM network
Multicast
SPBM floods unknown customer unicast, unknown customer multicast, and broadcast as multicast traffic.
SPBM supports the following replication methods for multicast:
•Head-end replication—Replicates frames at the ingress BEB for frames to enter the SPBM network.
This method is suitable for SPB VSIs that have sparse multicast traffic. It does not require BCBs to
maintain multicast FDB entries.
•Tandem replication—Replicates frames only at the node where the shortest path tree forks. This
method is suitable for SPB VSIs that have dense multicast traffic. It requires BCBs to maintain
multicast FDB entries.
In head-end replication, the ingress BEB performs the following tasks, as shown in Figure 4:
1. Replicates the customer frame for each destination BEB.
2. Encapsulates each replica in one unicast frame.
3. Sends the unicast frames to the destination BEBs.
Customer
network
BEB 1 BEB 2
SPBM network
BCB
GE1/0/1 GE1/0/1 GE1/0/2 GE1/0/1
CNP CNP
B-DA
BEB2 Data
B-SA
BEB1 B-VLAN 100 I-SID 300
Encapsulate frame
with B-MACs, B-
VLAN, and I-SID
Forward based on
destination B-MAC
and B-VLAN
Remove outer header
(B-MACs, B-VLAN,
and I-SID)
B-MAC
BEB2
B-VLAN
100 GE1/0/1
Port
BEB2
BEB1 100
100
GE1/0/1
GE1/0/2
B-MAC B-VLAN Port B-MAC
BEB1
B-VLAN
100 GE1/0/1
Port
Data Data
Customer
network
B-DA
BEB2 Data
B-SA
BEB1 B-VLAN 100 I-SID 300

7
Figure 4 Head-end replication
In tandem replication, the source BEB encapsulates a frame with a B-DA multicast address that uniquely
identifies itself and the SPBM service. When this frame arrives at the BCB where the shortest path tree
forks, the BCB replicates one frame for each destination BEB, as shown in Figure 5.
Customer
network
Customer
network
BEB 1
BEB 2
SPBM network
BCB
CNP
CNP
B-DA
BEB2Data
B-SA
BEB1B-VLAN
100I-SID
300
Data
Data
Customer
network
B-DA
BEB2 Data
B-SA
BEB1 B-VLAN 100 I-SID 300
BEB 3
CNP
Data
B-DA
BEB3 Data
B-SA
BEB1 B-VLAN 100 I-SID 300
B-DA
BEB3Data
B-SA
BEB1B-VLAN
100I-SID
300
B-MAC
BEB2
B-VLAN
100
Port
BEB3 100
BEB2
BEB1 100
100
B-MAC B-VLAN Port
BEB3 100
B-MAC
BEB1
B-VLAN
100
Port
BEB2 100
B-MAC
BEB1
B-VLAN
100
Port
BEB3 100
GE 1/0/1 GE 1/0/1
GE1/0/2
GE1/0/3GE1/0/1
GE1/0/1
GE1/0/1
GE1/0/1
GE1/0/1
GE1/0/2
GE1/0/3
GE1/0/1
GE1/0/1
GE1/0/1
GE1/0/1

8
Figure 5 Tandem replication
SPBM multicast address
Each SPBM node has a multicast address for each SPB VSI. This multicast address consists of one shortest
path source identifier (SPSource ID) and one I-SID. The I-SID identifies an SPB VSI, and the SPSource ID
identifies the node as a multicast source in the SPB VSI.
By default, ISIS-SPB generates the SPSource ID automatically. You can configure the SPSource ID
manually, but the SPSource ID must be unique throughout the SPBM network.
Figure 6 SPBM multicast address format
Customer
network
Customer
network
BEB 1
BEB 2
SPBM network
BCB
CNP
CNP
B-DA
M-BEB1Data
B-SA
BEB1B-VLAN
100I-SID
300
Data
Data
Customer
network
BEB 3
CNP
Data
B-DA
M-BEB1 Data
B-SA
BEB1 B-VLAN 100 I-SID 300
B-DA
M-BEB1Data
B-SA
BEB1B-VLAN
100I-SID
300
B-MAC
M-BEB1
B-VLAN
100
Port
M-BEB2
M-BEB1 100
100
B-MAC B-VLAN Port
M-BEB3 100
B-MAC
M-BEB3
B-VLAN
100
Port
B-MAC
M-BEB2
B-VLAN
100
Port
GE 1/0/1 GE 1/0/1
GE1/0/1
GE1/0/3
GE1/0/2
GE1/0/1
GE1/0/1
GE1/0/2，GE1/0/3
GE1/0/1，GE1/0/3
GE1/0/1，GE1/0/2
GE1/0/1
GE1/0/1

9
Table 2 SPBM multicast address fields
Field Description
M 1-bit multicast flag. Its value is fixed at 1.
L 1-bit local flag bit. Its value is fixed at 1.
TYP 2-bit SPSource ID type. Its value is fixed at 0.
SPSource ID 20-bit SPSource ID.
I-SID 24-bit SPB VSI identifier.
In Figure 6, LSB represents the lower 4 bits of a byte, and MSB represents the higher 4 bits of a byte. The
first byte of an SPBM multicast address is identical to the combination of the first 4 bits of the SPSource
ID field, the TYP field, the L field, and the M field. For example, the hexadecimal form of the first byte (E3)
in the SPBM multicast address E386070006E9 is 11100011. This byte consists of 1110 (first 4 bits of
SPSource ID), 00 (TYP), 1 (L), and 1 (M).
Multiple SPB VSIs
You can use multiple SPB VSIs to transmit traffic for different Ethernet services that span different customer
sites. Each SPB VSI is identified by a unique I-SID.
For example, the network in Figure 7 has the following SPB VSIs:
•I-SID 300 extends traffic to customer sites B, C, and D.
•I-SID 400 extends traffic to all customer sites.
•I-SID 500 extends traffic to customer sites A and D.
All traffic in one SPB VSI is transmitted in one B-VLAN. Different SPB VSIs can use the same B-VLAN to
transmit traffic. Traffic of different SPB VSIs is isolated by I-SID.

10
Figure 7 Multiple SPB VSIs
Load balancing
To balance traffic between forwarding paths, you can map B-VLANs to different ECT algorithms. When
a path is approaching congestion, you can move part of traffic on one path to another by moving an
I-SID from one ECT algorithm to another.
B-VLAN to ECT algorithm mapping
For balanced traffic distribution, SPBM supports calculating one SPT for a set of B-VLANs by using
different ECT algorithms. IEEE 802.1aq SPB provides 16 ECT algorithms. Each algorithm represents a set
of tie-break rules. As a result, you can have up to 16 forwarding paths in an SPBM network.
Figure 8 shows two SPTs that are calculated by using two ECT algorithms.
Customer site B
Customer site A
Customer site E
Customer site D
Customer site C
VSI 3
VSI 2
BEB
I-SID 400
I-SID 500
BEB
I-SID 300
I-SID 400
BEB
I-SID 400
BEB
I-SID 300
I-SID 400
I-SID 500
BEB
I-SID 300
I-SID 400
VSI 1
SPBM
network

11
Figure 8 Multiple SPTs in an SPBM network
ECT migration
ECT migration enables an I-SID to migrate from one ECT algorithm to another with minimum traffic loss.
To prevent traffic loss, ECT migration was designed based on the idea of make-before-break. All nodes
in the SPBM network maintain the old path for the I-SID before a new path is set up. The SPBM nodes
remove the old path only after all affected traffic has been moved from the old path to the new path for
the I-SID.
As shown in Figure 9, two paths (path A and path B) are available between BEB 1 and BEB 2. B-VLAN
300 has been using path A. As path A is getting congested, you can perform ECT migration to move part
of B-VLAN traffic (for example, traffic in I-SID 400) to path B.
Figure 9 ECT migration
Customer site B
Customer site A
Customer site F
Customer site E
Customer site C
BEB
BEB
BEB
BEB
BEB
Customer site D
BEB
BCB BCB
SPBM
network
ECT 1 B-VLANs 100-200
ECT 2 B-VLANs 300-400
BCB 1
BCB 2
Customer
network
Customer
network
BEB 1 BEB 2
SPBM network
Path A (ECT 1)
Path B (ECT 2)
I-SID 400 B-VLAN 300
B-VLAN 300 ECT 1
B-VLAN 300 ECT 2
B-VLAN 300 ECT 1
B-VLAN 300 ECT 2
CNP
I-SID 400 B-VLAN 300
B-VLAN 300 ECT 1
B-VLAN 300 ECT 2
CNP

12
Loop prevention
SPBM nodes collect topology data independently to calculate forwarding paths. Transient loops might
occur during SPT recalculation caused by a network flapping because the latency varies for an LSP to
reach the SPBM nodes. SPBM uses the Agreement Protocol (AP) to prevent transient loops. AP introduces
a delay for ISIS-SPB to issue forwarding entries to the data plane. After a topology recalculation, ISIS-SPB
issues new forwarding entries to the data plane only if topology data is synchronized between the SPBM
node and its adjacent neighbors.
NOTE:
In this document, "AP" refers to agreement protocol. In other documents, "AP" can also refer to access
points.
Multicast B-VLAN
By default, the device uses one B-VLAN to transmit both unicast and multicast traffic. If tandem multicast
replication is used, you must enable the multicast VLAN feature for the device to use separate VLANs for
unicast and multicast traffic.
If the multicast B-VLAN feature is enabled, you must assign an odd B-VLAN ID to an I-SID for SPBM to
transmit unicast traffic. SPBM automatically chooses the next higher even B-VLAN ID (odd B-VLAN ID plus
1) for multicast traffic.
ISIS-SPB only advertises the odd B-VLAN IDs. It uses the odd B-VLAN IDs when populating the unicast
FDB table with routes. When populating the multicast FDB table with routes, it uses the even B-VLAN IDs.
Fast channel for quick spread of LSPs
The fast channel feature provides a quicker LSP propagation method than conventional LSP propagation.
This feature spreads ISIS-SPB LSPs in the SPBM network by forwarding LSPs as data packets along the SPT
in a dedicated SPB VSI. An SPBM node does not need to complete updating its LSDB before it
propagates the topology change to the next node.
The I-SID for the fast-channel VSI is 255. To use the fast-channel feature, you must create a VSI and assign
I-SID 255 to the VSI.
You cannot associate any Ethernet service instance with the VSI that uses I-SID 255 for data transmission.
Protocols and standards
•IEEE 802.1aq, Shortest Path Bridging
•IEEE 802.1ah, Virtual Bridged Local Area Networks Amendment 7: Provider Backbone Bridges
•ISO 10589, ISO IS-IS Routing Protocol
•RFC 6329, IS-IS Extensions Supporting IEEE 802.1aq Shortest Path Bridging