[e2e] "PMTUD using options" draft

[RJ Atkinson]

On Feb 12, 2004, at 08:55, Michael Welzl wrote:
> A local copy + some measurement results on the overhead
> caused by option processing in routers can be found at:
> http://www.welzl.at/research/projects/ip-options/

It is widely believed that all routers process IP packets
with options in the "slow path", as you claim in your web
site above.  This should be re-filed in the basket of
"widely believed fallacy". :-)

In fact, this is no longer true (if it ever was).  It is true
for certain widely used routers that rely on CPU-based forwarding.
CPU-based forwarding is probably dying out in routers not sold
in retail consumer electronics stores (and maybe even there).

However, many other firms have hardware-based forwarding engines
that include the ability to process packets containing IP options
in the hardware fast path.  Some of the better hardware-based
forwarding engines are programmable, to varying degrees, so
adding support for new IP options in the hardware fast path
might be as simple as putting new microcode into a router
system software image.

Whether such implementers would be motivated to implement
support for any particular new IP option is probably driven
mainly by economics.  Most firms have long lists of new features
that customers desire and finite development resources.

Yours,

Ran Atkinson
rja at extremenetworks.com

Disclaimer: Employed by, but not speaking for, Extreme Networks.