RIB and FIB tables

[ncnaveen_arasu]

Hi Team

Please let me know the diffrence between RIB and FIB. when do we use these two.

What are the tables CEF contains and when we use CEF.

Thanks in advance,

naveen

[paul driver]

Hello

RIB - Routing information base - sh ip route ( shows rib- Where routing table is built- CONTROL PLANE)

FIB - Forward Information base - sh ip cef

( where RIB looks when deceiding where to forward the traffic - DATA PLANE)

MPLS - FORWARDS PACKETS BASED ON FIB & LFIB TABLES (DATA PLANE)

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LIB - Label information Base - sh mpls ip bindings

(Is where all mpls labels are known and mapped from FIB -  CONTROL PLANE)

LFIB -Label Forwading Information Base - sh mpls forwarding table

(where LIB mostly looks when deceiding where to forward Labeled MPLS packets - LFIB is mostly built by FIB & LIB tables - DATA PLANE)

Note:

#####

All routers in MPLS domain have both FIB and LFIB tables but only edge routers use FIB

(ingress router uses FIB, egress router uses LFIB and FIB)

Ingress LSR -  lookup is against the FIB

Egress LSR - lookup is against the FIB only if there was a single label in the stack

         and that this label was popped by penultimate hop, Rest of the time lookup is against the LFIB

Core mpls - lookup is against the LFIB

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[AinsleyBrown]

Simple and easy explanation for an otherwise confusing subject

[InayathUlla Sharieff]

Naveen,

In layman terms:

Both RIB and FIB in work concept they are similar functions both use to find the proper interface to which the input interface should send the packet to be transmitted out of the device(Router/Switch).

RIB works at the control plan as said above. RIB are optimized for efficient updating by Routing Protocols and other control plane infomration and it contains complete list of routes which is learned by the router.

FIB =Works at DATA Plane. FIbs are optimized for fast lookup of destination address.

(AS you are aware that when you enable ip Cef the two tables will be created (FIB and Adjacency table) In short All the routes will be downloaded from the RIB to the FIB and have it on the data plane.)

Below is the great article on difference between these:

http://blog.ioshints.info/2010/09/ribs-and-fibs.html

http://web.eecs.umich.edu/~zmao/eecs598-4/notes/Lecture4.pdf

HTH

Regards

Inayath

[paulstone80]

To answer the point about CEF, CEF uses the FIB and an adjacency table.

Traditional packet forwarding on a router involves ingress packets being matched against the routing table to determine the next hop, and also examining the ARP table to determine the layer 2 address of the next hop so it can be written into the egress packet.

CEF uses the FIB and the adjacency table to bypass this process and speed up packet forwarding.

The FIB re-orders the routing table so the most specific routes are first, it also contains the next-hop address for each entry.

The adjacency table contains the layer 2 information for the next-hop addresses in the FIB.

These tables are learnt as packets are forwarded through the traditional routing process, and when an entry is entered into the table subsequent packets are forwarded based on the information in the FIB and adjacency table, thus speeding up the process forwarding. This is done using special hardware.

To view the CEF FIB use:
show ip cef [type mod/number | vlan vlan-id] detail

To view the adjacency table use:
show adjacency [type mod/number | vlan vlan-id] [summary | detail]

HTH

Paul


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