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IS-IS for IPv6

E-series routers support IPv6 routing for IS-IS. The IPv6 Reachability TLV propagates reachability information by flooding and is used in SPF calculations. The IPv6 Interface TLV is used for next hop calculation and is exchanged by means of IS-IS hello packets. A single SPF calculation computes both IPv6 and IPv4 routing tables.

IS-IS routers learn about their neighbors’ support for IPv6 through the ISO network layer IPv6 protocol identifier, NLPID 142. The NLPID is contained in the NLPID TLV and is sent out in IS-IS hello packets when IS-IS IPv6 routing is enabled on an interface. A mismatch in support prevents an IS-IS adjacency from being established, because both neighbors must run the same protocols.

IPv6 aggregation, leaking, redistribution, export policies and import policies are supported similarly as for IP, but must be configured within the IS-IS IPv6 address family.

Graceful restart is supported for IS-IS IPv6 traffic depending on the availability of IPv6 high availability. It does not affect IP traffic.

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