IS-IS Filtering

Lessons Discussion
#1

This topic is to discuss the following lesson:

https://networklessons.com/cisco/ccie-routing-switching-written/is-is-filtering/

#2

Hi Rene,
We know that for Link state Routing Protocol "The database within an area has to be same " .I want to know more briefly about this why need the DB synchronized must ?? What issue will raise if not synchronized . Appreciate your very clear explanation as always .Thx

br//zaman

#3

Hello Zaman

A fundamental characteristic of Link State routing protocols is that every router constructs a map of the connectivity to the network that indicates which nodes are connected to which other nodes. This map is contained within the database. Based on this map, each router independently calculates the next best logical path from it to every possible destination on the network. These collections of best paths are then used to populate the routing table on the router.

If the database is not the same in all routers within an area, then there can be several negative consequences:

  1. Routers share information with their neighbours. If one router has an incomplete map of the network, it can give incorrect information to its neighbours, thus overwriting potentially correct routing information.
  2. Incorrect or incomplete maps of the network may also result in routing loops which can be devastating to the operation of the network.
  3. Incomplete maps can also cause the network never to converge, thus each router will use up resources in continually changing routing information or waiting for updated routing information that will never arrive.

I hope this has been helpful!

Laz