Is the routing table a control plane concept or a data plane concept?

[Mitrixsen]

Hello, everyone!

I've always been told that the routing table is a control plane concept. You build this table, collect the routes, the way they were learned, their metrics, and so on.

You then use this information to build a more forwarding-suitable table, the forwarding information base (FIB) which is a CEF concept. This table is then what's actually used o perform route lookups and is optimized for forwarding data.

However, this doesn't work the same if CEF is disabled. If CEF is disabled, process-switching takes place. With process-switching, there is no FIB, so the device actually performs a route lookup in the routing table this time, right?

So with process-switching, doesn't this make the routing table also a part of the data plane?

Thank you in advance.

David

Note: I understand that CEF should not be disabled, I just want to know this from a theoretical perspective.

[balaji.bandi]

OLD days from my noted : Process switching is a switching  methodology used by routers and Layer 3 switches where all incoming packets are examined by the main CPU and all forwarding decisions are made in software.

If the CEF not used then it uses more CPU to Punt - so recent most of the design CEF enable default on new Latest OS.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/44sg/configuration/guide/Wrapper-44SG/cef.html#wp1142909

[freefirnames12]

ke CEF is turned off, the router goes back to using a method called process-switching. In this case, it goes directly to the routing table to figure out where to send data packets.So, yes, in process-switching situations, the routing table kind of becomes part of the data plane because it's used directly to move data around

[freefirnames12]

uter goes back to using a method called process-switching. In this case, it goes directly to the routing table to figure out where to send data packets.So, yes, in process-switching situations, the routing table kind of becomes part of the data plane because it's used directly to move data around

[Joseph W. Doherty · Accepted solution]

You've several misconceptions.

Firstly, with data structures, control plane and data plane overlap.  For example, building and maintaining the route table, RIB and/or FIB are all control plane.  Using a data structure, like the FIB, for actual packet forwarding, would be data plane.

FIB is not a CEF concept.  Process-switching, can use a FIB.  Although later IOS versions, now only support process-switching and CEF, that wasn't the case when Cisco first provided CEF.  Back then, the router would support process-switching, fast (path) switching and CEF.

A few references which you might find helpful:

2005: https://www.cisco.com/c/en/us/support/docs/ip/express-forwarding-cef/13706-20.html

2014: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipswitch_fswtch/configuration/15-s/isw-fswtch-15-s-book/isw-fast-swtchng-cnfg.html

https://cordero.me/ribs-and-fibs/

https://learningnetwork.cisco.com/s/question/0D53i00000KssjfCAB/routing-rib-vs-fib

Lot more information might be found searching the Internet.

[mohamedlamine]

The routing table is a control plane concept. It is used by routers to determine the best path for forwarding packets from one network to another. The data plane, on the other hand, is responsible for actually forwarding the packets based on the information in the routing table.