udp packet problem

[Brian Candler]

On Mon, Mar 27, 2006 at 10:56:30AM +0200, Tyrone at telecity.se wrote:
> We have a Freebsd 5.4 router doing traffic shaping on a vlan interface.
> 
> Problem is we can't receive UDP packets larger than 2K is this a
> limitation or a setting within IPFW?

* Show your exact setup: what version of FreeBSD, what types of NIC you
  have, how you have configured them, how you've configured ipfw etc.

* Show what makes you think that UDP packets larger than 2K are being
  dropped. (For example, show a tcpdump of packets on the incoming interface
  and on the outgoing interface. Show what program you're using to send
  UDP packets)

* Preferably, boil this down to a simple test which demonstrates the problem
  in the simplest possible way. For example, if you turn off ipfw completely
  and can still demonstrate the problem, then this shows that ipfw is not
  at fault.

> How can I fragment UDP packets that are larger than the interface MTU ?

This happens automatically when sending packets. Inbound packets which are
larger than the configured MTU but successfully received, are accepted and
not modified. But outbound packets which are larger than the MTU of the
interface they are about to be sent out from, are fragmented.

> kernel option or FW ruleset ?

No, it just happens (unless you can demonstrate otherwise).

Once you have a more accurate description of your problem, freebsd-net is
probably a better place to post it.

HTH,

Brian.