Diffs between forwarding table and route table

[addylamlappun]

Hello Cisco gurus,

I look forward to learning from you guys and gals. Can someone please help me with the following:

- basic differences between an ip route table and ip forwarding table

- how are the entries in the two tables be different?

- what's in one table but not the other?

- what's the forwarding table for if we have a route table?

- it would be great if there is a doc on CCO that can help me understand the diffs.

Thanks in advance.

Ad.

[amit-singh]

Hi Ad,

Ip routing and Ip forwarding table is the same. I remember some vendor call the ip routing table as ip forwarding table in their implimentation. Extreme calls the routing table as ip forwarding table on their L3 switches.

If you are talking about the forwarding information base or FIB use in CEF then you can get a lot of information on that.

1. FIB is the image of the routing table which has the cache entries of the ip packet flows. When you enable CEF on the router the route entries gets downloaded and the respective flows as hardware switches from a particular source to a destination.

2. FIB has the entires of the flows prefix along with the next hop ip address and the attached interface.

3. FIB has the cached flows and the respective traffic is hardware switched and faster look up is done then the look ups in routing table.

Here are the few docs .

http://www.cisco.com/warp/public/cc/pd/iosw/iore/tech/cef_wp.htm

http://www.cisco.com/en/US/partner/products/hw/modules/ps2033/prod_technical_reference09186a00800afeb7.html

HTH,

-amit singh

[kamlesh_s1181]

HI addylamlappun,

Well this the difference that i got from RFC is

The IP Forwarding Table is quite analogous to the older ipRoute

Table. The principal differences are:

(1) It is somewhat re-organized, for aesthetic reasons,

(2) It has the Next Hop Autonomous System Number, usefulprimarily to the administrators of regional networks,

(3) It is instanced by Policy and Next Hop as well as by ultimate destination. Thus, multiple multipath routes can be managed, not just a single route, along with the circumstances under which the any given route might be chosen.

http://www.faqs.org/rfcs/rfc1354.html

According to configured route-map or policy based routing forwarding information base is changed.

BOL

Kamlesh sharma