If an ISP is doing port 25 blocking, when I try to test getting through my firewall to my mail server by telnetting on port 25, will that get blocked too?
I have rules to allow SMTP traffic through and was trying to test them with this method and I saw nothing on my ACL firewall hits. I have been very confused by this for several days. Then I tried to telnet into port 25 on a company that i used to work for where this worked (using a different ISP for connection) and it timed out.
Thanks.
Yes, by definition. If the ISP allowed you through then they aren't doing "port 25 blocking".
Timing out is a typical reaction for a firewalled connection. Most firewalled connections do not send RST or ICMP Unreachable packets in response to connection attempts, so it is left to the client TCP to eventually give up on receiving an answer (just as if the packet had been routed into never-never land or dropped.)
But I should see some hits on my permit statements in my ACL if it was making it through and if everything was working correctly, i would see the SMTP server.
If they are port 25 blocking, that would prevent my telnet attempt, correct?
Thanks.
Walter Robers> > >If an ISP is doing port 25 blocking, when I try to test getting through
Yes.
Your reference to the other company said you tried to telnet -to- them from a different ISP, not that you tried to telnet to your own machine -from- that company. If they are firewalled, then when you try to connect to them, you would expect the timeout, because of the arrangements on their end (or because of their ISP.) In the case of connecting to them, your PIX would not be involved unless you were starting from inside your PIX, in which case you'd only get a hit on your ACL permit for an ACL applied "in interface inside"
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