About IS-IS
IS-IS is an Interior Gateway Protocol (IGP) based on Standardization (ISO)/International Engineering Consortium (IEC) 10589 and RFC 1995. Cisco NX-OS supports Internet Protocol version 4 (IPv4) and IPv6. IS-IS is a dynamic link-state routing protocol that can detect changes in the network topology and calculate loop-free routes to other nodes in the network. Each router maintains a link-state database that describes the state of the network and sends packets on every configured link to discover neighbors. IS-IS floods the link-state information across the network to each neighbor. The router also sends advertisements and updates on the link-state database through all the existing neighbors
Segment routing on the IS-IS protocol supports the following:
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IPv4
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Level 1, level 2, and multi-level routing
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Prefix SIDs
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Multiple IS-IS instances on the same loopback interface for domain border nodes
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Adjacency SIDs for adjacencies