[c-nsp] Packet Fragmentation

[Lukas Tribus]

> Currently, using Cisco 3800's. Unfortunately, because the traffic is UDP,
> mss adjust can't be used to adjust the frame size. The fragmentation is
> unavoidable as this involves VPNs and the applications can't be adjusted to
> try smaller sized frames.
>
> Are there any documents that show the impact for each platform? I can find
> pps, throughput, etc... but nothing says how fragments impact things.

Of course not, its software processed and unpredictable.

Avoid MTU mismatches, switch to IPv6, set the DF-bit on UDP traffic (to invoke
PathMTU) - or - if thats not possible at all, buy boxes with bigger CPU. Behavior
will still be unpredictable, but an ISR G2 can probably fragment a few mbit/s of
traffic.

If PPPoE is the problem, use rfc4638/ppp max payload.


Lukas