"Ian C. Sison" wrote:
> Hello all,
>
> I'm having problems receiving mail from certain sites on the net,
> apparently their servers cannot connect to the servers i administer via
> smtp, and times out.
>
> Looking at netstat, i see a lot of SYN_RECV sessions going on sometimes up
> to 100+ sessions all from servers from that particular site that cannot
> send mail to me. This is really strange because all the other sites can
> send me email, only particular ones fail. And no, it's not a bandwidth
> problem..
>
> Anybody know what the source of the SYN_RECV sessions are and why they
> hang only for particular sites on the net?
>
> Signed,
>
> Puzzled \8(
>
ian,
SYN_RECV is a part of a three-way handshake. the remote side is sending a
SYN(chronize) packet to establish a
connection at your side. after receiving that SYN packet at your side, it
ACK(nowledge) and the same time sending a
SYN packet back from the remote side while you are now in the SYN_RECV state until the
remote side ACK it. this is
called a three-way handshake. when the remote site ACK it, an ESTABLISHED connection
comes next.
try to run "tcpdump host <ipaddress of remote side>" and from the remote side, do
a "telnet <your ip address> 25"
and give it to me the tcpdump output for packet analysis so that i could explain it to
you the causes of your problem.
fooler.
_
Philippine Linux Users Group. Web site and archives at http://plug.linux.org.ph
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