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The first CCIE Journey

IS-IS Protocol

IS-IS Standards History
 ISO 10589 specifies OSI IS-IS routing protocol for CLNS traffic
Tag/Length/Value (TLV) options to enhance the protocol
A Link State protocol with a 2 level hierarchical architecture.
 RFC 1195 added IP support
I/IS-IS runs on top of the Data Link Layer
Requires CLNP to be configured
 RFC5308 adds IPv6 address family support to IS-IS
 RFC5120 defines Multi-Topology concept for IS-IS
Permits IPv4 and IPv6 topologies which are not identical

ISIS Levels
 ISIS has a 2 layer hierarchy
Level-2 (the backbone)
Level-1 (the areas)
 A router can be
Level-1 (L1)  router
Level-2 (L2)  router
Level-1-2 (L1L2) router

ISIS Levels
 Level-1 router
Has neighbours only on the same area
Has a level-1 LSDB with all routing information for the area
 Level-2 router
May have neighbours in the same or other areas
Has a Level-2 LSDB with all routing information about inter-area
 Level-1-2 router
May have neighbours on any area.
Has two separate LSDBs: level-1 LSDB & level-2 LSDB




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