tech-net archive

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Old Index]

Re: IPV6 router works, but clients fail

>>>>> "rm" == Roy Marples <> writes:

    >> net.inet.tcp.mss_ifmtu = 1 
    >> net.inet6.tcp6.mss_ifmtu = 1

    rm> My understanding is that only works on the router and not the
    rm> ones connected by NAT. [...]

if you weren't changing MTU on your ethernet segment that'd be true.

but in your case, no:

    rm> Maybe I'll look into allowing NetBSD to use the MTU as
    rm> advertised by rtadvd as it currently ignores it.

the above sysctl's are likely to do exactly this.

MTU != mss

MTU is for all protocols and controls what you are allowed to send.

mss is for TCP only, and advises the other end about what you are
prepared to receive.

If you presume asymmetric routing, what you are prepared to receive
doesn't necessarily have anything to do with what you are allowed to
send.  so NetBSD may well be obeying the mtu in rtadv's, but even if
it were, this would cause no change in the mss (with the default '0'
setting of those sysctl's) and would not solve your problem.

The sysctl's say, ``go ahead and make the assumption that the receive
path uses the same interface as the send path,'' so NetBSD will
calculate an mss based on IP + TCP overhead and the MTU of the route
for sending TO the peer.

of course there could easily be two problems...

Attachment: pgpfQgZlu3kQU.pgp
Description: PGP signature

Home | Main Index | Thread Index | Old Index