What Is the difference between RIB and the global routing table

hitmen

I am only aware of the difference between the global routing table and the vrf routing table.

joetest

I think technically every routing protocol has it's own RIB(routing information base aka routing database).

And each of the best routes from all the routing protocols(based prefix length, AD or metric depending) makes up the routing table, or main RIB/Global routing table.

Makes sense?

hitmen

Hi joetest,

I understand that the FIB is parsed from the RIB.

Is the main RIB/Global routing table same as the FIB???

I am confused here. Pls advise.

SecurityThroughObscurity

If different routing tables are maintained, such as in an MPLS VPN environment, each VPN has its own FIB. The FIB is not data-driven. Rather, it is created and updated by the routing table.

hitmen

Hi, are you referring to VRF table?

SecurityThroughObscurity

Yes, I am.

lrb

In a lot of cases when you are learning about the difference between the RIB and FIB you will see a pretty similar result when looking at the RIB and FIB entry for a route to a network and this is because the next hop in IGPs is typically the advertising router's interface on the same subnet the local router is on.

However, BGP sessions are created between routers that do not have to be directly connected and hence the BGP NEXT_HOP value may not necessarily be the IP next hop when performing the actual data forwarding. In this case, the RIB for a BGP entry may have a next hop IP address of 1.1.1.1 but the FIB may have the same route but to a next hop of 10.0.12.1, which is the actual next hop router to reach the network which was originally advertised through BGP. This is what most texts refer to when they discuss the BGP route recursion function. The FIB allows for this pre-computed resolution to be used for data forwarding.

Also the FIB doesn't store related admin distances and routing protocol metrics because these attributes are not important for actual data forwarding, they just help a router determine which route should be used when multiple routes exist to a network. That is, they are function of the RIB, not the FIB.