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IS-IS is a link-state interior gateway routing protocol which is described in ISO10589, RFC 1195, RFC 5308. Like OSPF, IS-IS runs the Dijkstra shortest-path first (SPF) algorithm to create a database of the network’s topology and, from that database, to determine the best (that is, shortest) path to a destination. The routers exchange topology information with their nearest neighbors. IS-IS runs directly on the data link layer (Layer 2). IS-IS addresses are called NETs and can be 8 to 20 bytes long, but are generally 10 bytes long.
For example NET
The IS-IS address consists of three parts:
49The AFI value 49 is what IS-IS uses for private addressing.
- Area identifier:
0001IS-IS area number (Area1)
- System identifier:
1921.6800.1002For system idetifier we recommend to use IP address or MAC address of the router.
- NET selector:
00Must always be 00, to indicate “this system”.
This command defines the ISIS router behavior:
level-1 Act as a station router only. level-1-2 Act as both a station router and an area router. level-2-only Act as an area router only.
This command sets old-style (ISO 10589) or new-style packet formats:
narrow Use old style of TLVs with narrow metric. transition Send and accept both styles of TLVs during transition. wide Use new style of TLVs to carry wider metric.
This command specifies circuit type for interface:
level-1 Level-1 only adjacencies are formed. level-1-2 Level-1-2 adjacencies are formed level-2-only Level-2 only adjacencies are formed
Simple IS-IS configuration using 2 nodes and redistributing connected interfaces.
set interfaces dummy dum0 address '203.0.113.1/24' set interfaces ethernet eth1 address '192.0.2.1/24' set policy prefix-list EXPORT-ISIS rule 10 action 'permit' set policy prefix-list EXPORT-ISIS rule 10 prefix '203.0.113.0/24' set policy route-map EXPORT-ISIS rule 10 action 'permit' set policy route-map EXPORT-ISIS rule 10 match ip address prefix-list 'EXPORT-ISIS' set protocols isis FOO interface eth1 set protocols isis FOO net '49.0001.1921.6800.1002.00' set protocols isis FOO redistribute ipv4 connected level-2 route-map 'EXPORT-ISIS'
set interfaces ethernet eth1 address '192.0.2.2/24' set protocols isis FOO interface eth1 set protocols isis FOO net '49.0001.1921.6800.2002.00'
Show ip routes on Node2:
vyos@r2:~$ show ip route isis Codes: K - kernel route, C - connected, S - static, R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP, T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP, F - PBR, f - OpenFabric, > - selected route, * - FIB route, q - queued route, r - rejected route I 203.0.113.0/24 [115/10] via 192.0.2.1, eth1, 00:03:42