Huawei S6700 Series Configuration Manual page 256

S6700 Series Ethernet Switches
Configuration Guide - IP Routing
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IS-IS HSB
The switch of a distributed architecture supports IS-IS HSB. In the IS-IS HSB process, IS-IS
backs up data from the active main board (AMB) to the standby main board (SMB). Whenever
the AMB fails, the SMB becomes active. This ensures uninterrupted running of IS-IS.
In the IS-IS HSB process, IS-IS configurations on the AMB and the SMB are consistent. After
a master/slave AMB/SMB switchover, IS-IS on the current AMB performs GR, obtains
adjacencies from its neighbors, and synchronizes its link state database (LSDB) with the LSDB
on the SMB. This prevents service interruption.
Local MT
When multicast and Multi-Protocol Label Switching (MPLS) TE tunnels are deployed on a
network, multicast may be affected by TE tunnels, which causes multicast services to become
unavailable.
This is because the outbound interface of a route calculated by an Interior Gateway Protocol
(IGP) may not be the actual physical interface but a TE tunnel interface after the TE tunnel is
enabled with IGP Shortcut. Based on the unicast route to the multicast source address, a
switch sends a Join message through a TE tunnel interface. In this situation, switchs spanned by
the TE tunnel cannot detect the Join message, so they do not create any multicast forwarding
entry. A TE tunnel is unidirectional, so multicast data packets sent by the multicast source are
sent to the switchs spanned by the tunnel through physical interfaces. These switchs discard the
multicast data packets, because they do not have any multicast forwarding entry. As a result,
services become unavailable.
To solve this problem, you can enable local MT to create a separate Multicast IGP (MIGP)
routing table for multicast packets.
IS-IS MT
IS-IS MT, a set of independent IP topologies, is an optional mechanism within IS-ISs used today
by many ISPs for IGP routing. This MT extension can be used for a variety of purposes, such
as an in-band management network "on top" of the original IGP topology, maintaining separate
IGP routing domains for isolated multicast or IPv6 islands within the backbone, or forcing a
subset of an address space to follow a different topology. Complying with RFC 5120, IS-IS MT
defines new type-length-values (TLVs) in IS-IS packets to transmit multi-topology information.
A physical network can be divided into different logical topologies as needed. Each logical
Issue 01 (2012-03-15)
Multi-process
Multi-process allows a group of interfaces to be associated with a specific IS-IS process.
This ensures that the specific IS-IS process performs all the protocol-based operations only
on the group of interfaces. Multiple IS-IS processes can run on a single switch and each
process is responsible for a unique group of interfaces.
Multi-instance
After the VPN feature is enabled, multi-instance allows an IS-IS process to be associated
with a specific VPN instance so that all the interfaces of this IS-IS process will be associated
with the VPN instance.
NOTE
For details about local MT, see the "IS-IS" chapter in the S6700 Series Ethernet Switches Feature
Description-IP Routing.
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