H3C Technologies H3C S12500 Series Switches - Manual (Page 159)

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Code 1 to 10 of CLV are defined in ISO 10589 (code 3 and 5 are not shown in the table), and others
are defined in RFC 1195.
Supported IS-IS features
Multiple instances and processes
IS-IS supports multiple instances and processes. Multiple processes allow an IS-IS process to work in
concert with a group of interfaces. This means that a router can run multiple IS-IS processes, and each
process corresponds to a unique group of interfaces.
For routers supporting VPN, each IS-IS process is associated with a VPN instance, which means the VPN
instance is also associated with interfaces corresponding to the process.
Active/Standby failover
IS-IS backs up necessary data from the active main processing unit (MPU) to the standby MPU.
Whenever the active MPU is down, the standby MPU can switch to the active status to run IS-IS.
The backup modes are as follows:
• Nonstop routing (NSR)—Backs up all IS-IS data. After active/standby failover, IS-IS can work
immediately.
• Graceful restart (GR)—Backs up only the configuration of IS-IS. After active/standby failover, IS-IS
performs graceful restart (GR) to synchronize the LSDB with neighbors.
IS-IS Graceful Restart
Graceful Restart (GR) ensures the continuity of packet forwarding when a routing protocol restarts or an
active/standby switchover occurs:
• GR restarter—Graceful restarting router. It must be GR capable.
• GR helper—A neighbor of the GR restarter. It helps the GR restarter to complete the GR process.
After an IS-IS GR restarter restarts, it must complete the following tasks to synchronize the LSDB with its
neighbors:
• Obtain IS-IS neighbor information without changing adjacencies.
• Obtain the LSDB.
To complete these tasks, the GR restarter sends an IS-IS GR signal to GR helpers so that the GR helpers
keep their adjacencies with the GR restarter, and then restores the neighbor table after receiving
responses from neighbors.
After that, the GR restarter synchronizes the LSDB with all GR-capable neighbors, calculates routes,
updates its routing table and forwarding table, and removes stale routes. The IS-IS routing convergence
is then complete.
IS-IS NSR
NSR is a new feature that overcomes the application limit of GR. It backs up IS-IS link state information
from the active MPU to the standby MPU. Upon an active/standby switchover, NSR can complete link
state recovery and route re-generation without requiring the cooperation of other devices.
IS-IS TE
IS-IS traffic engineering (TE) creates and maintains the Label Switched Path (LSP).