Port 25 blocking ????

Discussion in 'Cisco' started by K.J. 44, Sep 12, 2006.

  1. K.J. 44

    K.J. 44 Guest

    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.
    K.J. 44, Sep 12, 2006
    #1
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  2. In article <>,
    K.J. 44 <> wrote:
    >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?


    Yes, by definition. If the ISP allowed you through then they aren't
    doing "port 25 blocking".


    >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.



    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.)
    Walter Roberson, Sep 12, 2006
    #2
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  3. K.J. 44

    K.J. 44 Guest

    Re: Port 25 blocking ????

    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 Roberson wrote:
    > In article <>,
    > K.J. 44 <> wrote:
    > >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?

    >
    > Yes, by definition. If the ISP allowed you through then they aren't
    > doing "port 25 blocking".
    >
    >
    > >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.

    >
    >
    > 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.)
    K.J. 44, Sep 12, 2006
    #3
  4. Re: Port 25 blocking ????

    In article <>,
    K.J. 44 <> wrote:
    >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?


    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"
    Walter Roberson, Sep 12, 2006
    #4
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