Does PMTU always take 3 secs

Hello,

Studying packet traces between a client/server communicating over a GRE
tunnel there appears to be a characteristic 3 second delay before the
communication proceeds.

According to the Microsoft White Paper

www.microsoft.com/technet/prodtechnol/
windowsserver2003/technologies/networking/tcpip03.mspx

PMTU will take place by default. Consistent with this I see the tcp
handshake complete with an MTU of 1500, then the first two packets of data
are sent at this size (as per slow start initial window size). Two ICMP
Destination Unreachable packets are returned by the tunnel endpoint router,
but the server re-packages and sends only the first one. Then both ends wait,
until after 3 secs the client decides its not going to get another packet so
sends a re-request. The server then begins again, but at the smaller MTU, so
everything is OK - albeit 3 secs late.

The problem seems to be that the server does not react correctly to the ICMP
messages - does anyone know if I am missing a setting that would make this
work properly.

Regards