Port 135/137/139/445... Help me out here.....
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Thread: Port 135/137/139/445... Help me out here.....

  1. #1
    AO Ancient: Team Leader
    Join Date
    Oct 2002

    Port 135/137/139/445... Help me out here.....

    Ok..... I'm probably being really friggin' dumb..... It happened once before......

    With regard to the above mentioned ports and the services they provide is there _any_ good reason for allowing them to egress from your private network to the public internet, _ever_????? I have had them blocked from egress since before I can remember and have never had a problem. Until recently I had inbound 137/139/443 on an autoblock for three days, (ya, I'm aware of the potential for a DoS but I thought I could live with it.....), and with the advent of the MSBlaster worm I chose to stick 135 on the list too.

    The reason for the question???? So far my FW has put at least 5 mail servers on it's blocked list in the last 36 hours due to the fact that just after my server makes it's outbound port 25 connection to pass mail the damned receiving server is sending some unassociated request on port 137.... The result is an instant block on the site and no mail goes through. The remote mail servers just try to connect back to the mail server on 137 even though a good session is established on port 25 and it is running along just fine......

    It's frustrating the crap out of me having the phone keep ringing for undelivered mail and I really don't understand why these systems are allowing a 137 NetBIOS request out of their networks......
    Don\'t SYN us.... We\'ll SYN you.....
    \"A nation that draws too broad a difference between its scholars and its warriors will have its thinking done by cowards, and its fighting done by fools.\" - Thucydides

  2. #2
    Master-Jedi-Pimps0r & Moderator thehorse13's Avatar
    Join Date
    Dec 2002
    Washington D.C. area

    Firewall administrators will frequently see large numbers of incoming packets to port 137. This is due to the behavior of Windows servers that use NetBIOS (as well as DNS) to resolve IP addresses to names using the "gethostbyaddr()" function. As users behind the firewalls surf Windows-based web sites, those servers will frequently respond with NetBIOS lookups.

    We allow it outbound for the reasons mentioned above but we did close down 135, 69 and 4444 as to not help spread the blaster worm.
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