138
CLV Code
Name
PDU Type
132
IP Interface Address
IIH, LSP
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. 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. The VPN instance is
also associated with interfaces of the process.
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.
The GR Restarter sends an OSPF GR signal to GR Helpers so that the GR Helpers keep their adjacencies
with the GR Restarter, and restores the neighbor table after receiving responses from neighbors. The GR
Restarter then 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
Nonstop routing (NSR) is a new feature that overcomes the application limit of GR. It backs up IS-IS link
state information from the master device to the slave device. When a master/slave switchover occurs,
NSR can complete link state recovery and route re-generation without requiring the cooperation of other
devices.
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.
LSP fragment extension
IS-IS advertises link state information by flooding LSPs. Because one LSP carries a limited amount of link
state information, IS-IS fragments LSPs. Each LSP fragment is uniquely identified by a combination of the
System ID, Pseudonode ID (0 for a common LSP or a non-zero value for a Pseudonode LSP), and LSP
Number (LSP fragment number) of the node or pseudo node that generated the LSP. The one-byte LSP
Number field, allowing a maximum of only 256 fragments to be generated by an IS-IS router, limits the
amount of link information the IS-IS router can advertise.
