H3C Technologies H3C S7500E Series Switches - Manual (Page 159)

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Hot standby
A distributed router supports IS-IS Hot Standby (HSB). The data is copied from the Active Main Board
(AMB) to the Standby Main Board (SMB). Whenever the AMB is down, the SMB can switch to the
active status to run IS-IS.
There are two kinds of IS-IS HSB. One is IS-IS data synchronization backup. After switching from AMB
to SMB, IS-IS can work immediately.
The other HSB is to backup only the configuration information of IS-IS during the switching from AMB
to SMB. After the graceful restart (GR), the IS-IS router will send requests to neighbors to synchronize
the LSDB.
IS-IS Graceful Restart
Graceful Restart ensures the continuity of packet forwarding when a routing protocol restarts or an
active/standby switchover occurs:
z GR Restarter: Graceful restarting router. It must be Graceful Restart capable.
z GR Helper: The neighbor of the GR Restarter. It helps the GR Restarter to complete the GR
process.
After an IS-IS GR Restarter restarts IS-IS, it needs to complete the following two tasks to synchronize
the LSDB with its neighbors.
z To obtain effective IS-IS neighbor information without changing adjacencies.
z To obtain the LSDB contents.
After the restart, the GR Restarter will send an OSPF GR signal to its neighbors to keep the
adjacencies. After receiving the responses from neighbors, the GR Restarter can restore the neighbor
table.
After reestablishing neighborships, the GR Restarter will synchronize the LSDB and exchange routing
information with all adjacent GR capable neighbors. After that, the GR Restarter will update its own
routing table and forwarding table based on the new routing information and remove the stale routes.
In this way, the IS-IS routing convergence is complete.
IS-IS TE
IS-IS Traffic Engineering (TE) creates and maintains the Label Switched Path (LSP).
When creating the Constraint-based Routed LSP (CR LSP), MPLS needs to get the traffic attribute
information of all links in the local area. The Traffic Engineering information of links is obtained from
IS-IS.
For detailed configuration of the IS-IS TE, see MPLS TE Configuration in the MPLS Configuration
Guide.
Management tag
Management tag simplifies routing information management by carrying the management information
of the IP address prefixes (to control route redistribution from other routing protocols) and BGP
community and extended community attributes.