Conclusion of IS-IS Protocol
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| Fig 1: Conclusion of IS-IS |
- Area Tag (Optional and Alphanumeric).
- System ID (The Physical Address).
- Area ID ( 16/32 bits)
There are three types of the routers in the IS-IS:
- Level 1-2 routers have both role intra area and backbone.
- Level 1 routers are the intra area routers.
- Level 2 routers are the backbone routers.
Neighbor adjacencies are only built in between the same level routers. So the default level on the Cisco devices is Level 1-2. Every router generate the link state packets for each level that is configured. LSP contains the prefixes, neighbor adjacency, and metric. Level 1 LSPs are flooded with in area. Level 2 LSPs are flooded with in backbone area. Level 1-2 routers that are connected to the other area will set the attached bit in their level 1 LSP. Level 1 routers will generate the default route towards the level 1-2 router when they see the attached bit. Every router needs the Network Entity Title.
There are the four metric values:
- Default Metric
- Delay
- Expense
- Error
Cisco support the metric value default metric that is always 10 and that is the configurable parameter. IS-IS select the designated Intermediate system on the multi access networks and that selection on the base on the following points:
- Interface priority
- Highest SNPA
- Physical Address on a LAN
- DLCI on frame relay
- System ID
There is no backup of the designated Intermediate system if another router has the highest priority, then it will frequently take a role of DIS. The DIS is responsible for the creating the pseudonode there are two responsibilities of the pseudonode:
- Creating pseudonode LSP
- Creating the CSNP
Complete Sequence Numbers Protocol is sent every 10 seconds.Complete Sequence Numbers Protocol help the router to figure out the latest link state packets if they have otherwise, they request for updates to maintain the database.
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