[e2e] IP options over e2e path

Joe Touch touch at ISI.EDU
Wed Mar 29 21:31:10 PST 2006

Mikael.Latvala at nokia.com wrote:
> Hello, 
> First of all, thank you for the comments.
> http://www.icir.org/tbit/TCPevolution-Mar2005.pdf was indeed very
> interesting. Few comments about the paper.
> 1. It would be interesting to know whether routers along the packet path
> or the receiving server dropped the packets with different IP options. 
> 2. I disagree with "One concern is that the use of IP options may
> significantly increase the overhead in routers, because
> in some cases packets with IP options are processed on the slow path of
> the forwarding engine." because as RFC1812 says that routers can ignore
> the IP option, excluding source route, if so configured. This type of
> logic is very easy to implement on the fast path.

An IP packet with ANY options, i.e., one with a header length > 20, is
considered an exception and typically is processed in the slow path.

Slow-path processing embodies 'best effort' - it occurs only when the
router's CPU isn't busy doing something more important, including
running routing protocols, handling error messages, and monitoring

Granted, that accounts only for routers that drop 'some' or even 'most'
packets with options. Routers that drop _all_ packets with options are
either configured to do so or erroneous; it's hard to know for sure
which is happening where, though.


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