[OpenAFS] ADS communications issue?

Harald Barth haba@kth.se
Sun, 13 Sep 2009 12:02:07 +0200 (CEST)

> I'm suspecting the solution's in the network, not in AFS, however.  We
> just have to convince our network engineers (for the three networks the
> packets cross) to believe that. :)

Looks to me that you jumped into the juboframe boat without checking
the consequences at the border between the jumboframe - non-jumboframe
world. There correct fragmentation must be take place or the sending
part must ensure that depending on recipient, the right MTU is used.
My guess is that the packet with DF is part of an MTU discovery scheme
that is failing. (MTU discovery is generally failing in "the Internet"
because people filter ICMP traffic). I'm quite sure that sending
packets that are bigger than 1500 to any computer which in not on your
LAN or where you have control over the whole path will only give you
grief. So tune the OS/applications in that way.

BTW, there are people who claim that jumboframes >4k are harmful as
the checksum algorithm for ethernet is not very reliable for such big

You need to make sure that all interfaces on your LAN have the same
MTU and that the routers at the borders do the right thing for packets
that go between interfaces with different MTUs. ttcp (many
implementations available) and tcpdump are your friends.

Good luck,