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

[Chuck Lever]

Jim Rees wrote:
>   where is that rule stated?  most NFS clients i am aware of retransmit an 
>   RPC after 60 seconds over TCP.
> 
> Why would they do that?

because NFS/TCP implementations are usually based on pre-existing 
NFS/UDP implementations, which already have support for retransmitting. 
  also, see below: some clients might assume that a server could drop an 
RCP request coming over a TCP connection.

> I would consider that a bug.  I am only familiar
> with the various bsd implementations, but none of them retransmit over tcp.

Solaris and Linux both do it.  that doesn't mean it's the right thing to 
do.  however, there are reasons why that would make for some 
interoperability issues with servers that never drop.

> Are there buggy servers that drop rpc requests over tcp?  Why?

i don't know of a specific implementation that drops RPC requests over 
TCP.  however, i can think of some reasons (allowed by "holes" in the 
various RFCs) why a server implementor might think it's OK to do.