Spurious ACKs, ICMP unreachable?

[Mikolaj Golub]

On Fri, 13 May 2011 14:38:34 -0700 Chuck Swiger wrote:

 CS> On May 13, 2011, at 1:07 PM, Ivan Voras wrote:
 >> I'm seeing an an unusual problem at a remote machine; this machine is
 >> the FreeBSD server, and the client is a probably Windows machine (but I
 >> don't know the details yet). Something happens which causes FreeBSD to
 >> send ACKs to the client, and the client to send ICMP unreachable
 >> messages to the server. It is most likely a configuration error at the
 >> remote site but I have no idea how to verify this.


 CS> Let's look at just one connection:

 CS> 18:56:02.711942 IP server.http > client.4732: Flags [.], ack 2110905191, win 0, length 0
 CS> 18:56:02.713155 IP server.http > client.4732: Flags [.], ack 1, win 65535, length 0

 CS> The packet is FreeBSD webserver sending ACKs with zero window size;
 CS> that's a sign of congestion that the client should not be sending more
 CS> data and instead doing periodic window probes until the local box opens
 CS> the window again.  The next packet on the same connection then ACK's
 CS> something outside of the window with a 64K window size.  That's wrong;
 CS> the other side probably sends an RST and the ICMP error.  If you have TSO
 CS> enabled, try turning it off.

Might be this the thing that jhb@ was fixing in r221346?

-- 
Mikolaj Golub