[Sis-SCPS-INTEREST] Re: ZeroWindow segment

[travis at globalprotocols.com]

Miguel,

You may indeed have connectivity/configuration problems with the gateway,
but I believe that your SCPS-TP gateways are interacting properly.

I believe what you are seeing is the normal connection establishment
behavior
for the Reference Implementation of the SCPS-TP gateway.

The end-to-end TCP flow is split into 3 pieces:


   http client ----------> local GW ----------> remote GW -------> http
server

The local GW intercepts the SYN from the http client and immediately
opens a connection between the http client and itself (spoofing the http
server)
and then performs an active open to the http server on its own behalf;

In order to prevent the http client from sending any data until the local GW
knows it has a connection to (who it thinks is) the http server, it
advertises
a zero window to the http client.

When the local GW receives a SYN-ACK (and *maybe* a non-zero advertised
window)
in response to it's active open, it will send a window update to the
http client.

The same thing happens between the local and remote GWs.

If there is indeed a problem for the local or remote GWs to connect to their
"next hop" destination, you should receive a RST segment at the http client.


So, you should be seeing this zero-window advertised on the SYN-ACK from the
RI SCPS-TP gateway on all flows - even the successful ones.


Hope this helps understand what you are seeing.

Eric