Intermittan Port Conflicts

[AMSI007]

We have a site, with approximately 100 machines. They are using Outlook 2000, 2003, Outlook Express for POP3 e-mail.

The site is on a domain, running DHCP. The setting required by the POP3 provider, requires the use of port 995 for Incoming, and 465 for outgoing, with SSL. Every few days, outgoing e-mail to external domains no longer functions. The e-mail just sits in the outbox.

To rememdy the situation, the port settings need to be changed to 110 and 25. This works for a few days, then vice versa. Has anyone experienced this, or have any idea what might cause it? We've checked repeatedly with the mail provider, with whom we have 38 other sites that use the same service, and they have never experienced the issue. Leads me to believe it's a problem locally.

 

[KiscoKid]

Do you have a device locally translating between ports 995/110 and 465/25 for all connections to/from the mail server?

 

[AMSI007]

Not that I know of. We have a pix firewall at the edge of the network that is performing NAT, and the PDC is doing the DNS. As far as I know the pix is straight through doing no port forwarding. Other devices on the network include an AS/400 but we don't manage that. There's also two Cisco 1700 routers but they are only providing connectivity, no other functions are enabled.

 

[pansophic]

This is an easy problem to resolve, I've had the same issues with my hosting service, although never with that kind of regularity.

You can use hping to ping a TCP port. When you start getting failures for 465 (since you said that it was outgoing mail that was being affected) you need to test from outside our firewall to determine if the port is really closed, or if your firewall is blocking the connection requests.

I believe that hping has a traceroute like functionality that can be enabled allowing you to determine where in the network that packets are being dropped or rejected.

Netcat may work as well if you are really a Windows shop, but I don't believe that the traceroute functionality is available.


pansophic