IP header option

OK another dumb question,

in CEF packets with the IP header option can't be "switched" and are punted to the router process.

but exactly what is the header option? I thoughts it was to do with things like ICMP. But Now I am thinking that is completely wrong, would things like source routing be contained in options?

Any one care to fill in the knowledge gap for me please ?

Cheers

Find more posts tagged with

Save $250 on 2025 certification boot camps from Infosec!

Book now with code EOY2025

Button

Comments

Met44

Any packets using the "options" field in the IP header are off limits for CEF, so this includes things like source routing, route recording, and the timestamp request option. Note that the router must do extra "stuff" with any of these options (if such processing was not disabled) -- that's why the packet gets punted up to the more intelligent methods of dealing with packets. You could lab this out using extended ping commands to populate the IP header options and the show commands to view cef punts if it would help.

DevilWAH

Met44 wrote: »

Any packets using the "options" field in the IP header are off limits for CEF, so this includes things like source routing, route recording, and the timestamp request option. Note that the router must do extra "stuff" with any of these options (if such processing was not disabled) -- that's why the packet gets punted up to the more intelligent methods of dealing with packets. You could lab this out using extended ping commands to populate the IP header options and the show commands to view cef punts if it would help.

No that's cool I get the CEF processes and punting frames. I was just curious what IP/Routing features use the IP header options. I was wondering if there is a complete list of them anywhere.

Met44

That information can be found in the IP RFC, 791.