FreeBSD NFS server not responding to TCP SYN packets from Linux/SunOS clients

[rick at snowhite.cis.uoguelph.ca]

>   ps: It would be nice if someone with the right expertise could explore
>       other things in TCP specifically for NFS. For example, I don't see
>       why a retransmit timeout should go above about 100msec
> 
> nfs/rpc shouldn't retransmit at all over tcp except when there has been a
> reconnect.  Tcp might retransmit, but modern implementations will always
> choose the right timeout dynamically, unless packet loss is excessive.
> 
Yes, I was referring to TCP retransmits and I was suggesting that TCP
might not be "choosing the right timeout dynamically". A lot of what is
in TCP timers now dates back to work done w.r.t. congestion avoidance
(very good work, I might add) in the late 1980s. I don't know if anyone
has revisited this, now that almost everything is gigibit fibre (in the
late 1980s, there were still 56Kbps internet links out there).

I don't know enough about TCP (and haven't looked at recent literature),
but I do know that I see retransmit timeouts back off to 1-2sec quite
rapidly, as soon as I introduce a 20msec transit delay between
client<->server and throw away the odd packet. The result is abismal
NFS/TCP preformance.

rick