[e2e] "PMTUD using options" draft

[Sneha Kumar Kasera]

Hi,

I ran several experiments using IP packets with options in the mid 90's 
and observed considerable and unpredictable difference in the round trip 
delays of IP packets with and without IP options.

Even today after seeing this email and hoping that things might have 
changed, I tried " ping" and "ping -R" (the -R  is for the IP record 
route option) to some nodes several hops away and found significant 
difference in the round trip delays.

Here is a sample:

xxx.yyy.zzz is a university in the US (15 hops away)
ping -s xxx.yyy.zzz
round-trip (ms)  min/avg/max = 60/60/61

ping -s -R xxx.yyy.zzz
round-trip (ms)  min/avg/max = 109/156/211


xxx.yyy.zzz is a company in Europe (17 hops away)
ping -s xxx.yyy.zzz
round-trip (ms)  min/avg/max = 156/156/157

ping -s -R xxx.yyy.zzz
round-trip (ms)  min/avg/max = 181/260/401

Any comments?

Sneha

--
Sneha Kumar Kasera
http://www.cs.utah.edu/~kasera

RJ Atkinson wrote:

>
> 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.
>