IP Fragmentation - Not reliable over the Internet?

William Herrin bill at herrin.us
Tue Aug 27 17:45:02 UTC 2013


On Mon, Aug 26, 2013 at 8:01 PM, Christopher Palmer
<Christopher.Palmer at microsoft.com> wrote:
> What is the probability that a random path between two Internet
> hosts will traverse a middlebox that drops or otherwise barfs on
> fragmented IPv4 packets?

Hi Christopher,

I think there might be three rather different questions here:

1. If I originate IP packet fragments, such as an 8000 byte NFS packet
broken into 1500 byte fragments, what's the probability of some host
before the other endpoint dropping one or all of those fragments?

2. If I send an IP packet that's too large for the path and *don't*
set the don't-fragment bit, what' the chance that the router with the
too-small next hop will fail to correctly fragment that packet (or
that the correctly fragmented packet will fall into trap #1 above)?

3. If I send an IP packet that's too large for the path and *do* set
the don't-fragment bit, what's the chance of failing to receive the
"packet too big" message it causes the intermediate router to send?

Are you after the answer to one in particular?

Regards,
Bill Herrin



-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004



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