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IS-IS Router Types

Latest reply: Feb 7, 2019 13:55:11 1040 1 0 0 0

Routers are identified as Level 1, Level 2, or Level 1-2:

     Level 1 routers use LSPs to build topology for local area.

     Level 2 routers use LSPs to build topology between different areas.

     Level 1-2 routers act as border routers between Level 1 and Level 2 routing domains.

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  • convention:

Created Feb 7, 2019 13:55:11

IS-IS uses different areas where the entire router sits in an area, not just one of its interfaces like with OSPF. There is no backbone area, the backbone is formed by a string of routers.

There are three types of routers:

Level 1 system: this is an intra-area router, it only knows what the local area looks like and will only learn prefixes from its own area. It creates a level 1 link-state database and SPF tree for the area.
Level 2 system: this is a backbone router that knows all intra-area and inter-area routes. It creates a level 2 link-state database and SPF tree for the backbone.
Level 1-2 system: this is a router that performs both roles. It creates a separate level 1 and 2 link-state database and two SPF trees, one for each database.
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  • convention:


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