pmtud + ipnat RELENG_6_2 appears to be broken
cswiger at mac.com
Thu Jul 12 19:54:37 UTC 2007
On Jul 12, 2007, at 12:34 PM, Stephen Clark wrote:
> Did something change in 6.2? If my mtu size on rl0 is 1280 it won't
> accept a larger incoming packet.
Nothing changed; that is the expected behavior.
(Modulo support for 4-byte VLAN tags.)
> kernel: rl0: discard oversize frame (ether type 800 flags 3 len
> 1514 > max
> I don't think it worked this way in the past.
Well, it did. :-)
> Won't this affect pmtud?
> man page for ifconfig says mtu limits size of "transmission" not
> "mtu n Set the maximum transmission unit of the interface to
> n, default
> is interface specific."
The MTU is actually defined in reference to a network segment such as
an "ethernet collision domain", and applies to all machines sending
traffic to that segment. If the MTU is really 1280, nobody else
should be sending larger packets, and the drivers will drop any
larger packets they receive and generate the appropriate ICMP error....
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