(Solved) Strange dial-up related DNS problems

From: Willie Viljoen (will_at_unfoldings.net)
Date: 07/31/03

  • Next message: Konrad Heuer: "Re: [NEWBIE] Using external SMTP-Server for mail" 
    To: freebsd-questions@freebsd.org
Date: Thu, 31 Jul 2003 09:52:49 +0200

    I got it fixed (or atleast, as good as it can be fixed)

    For future reference, here's what went wrong.

    During the weekend, SAIX upgraded and repaired all Cisco equipment on their
    network. During this repair, they somehow managed to break something major.
    The /etc/ppp/options file on the offending BSD box contained the asyncmap 0
    option. This tells pppd not to escape characters leaving as part of packets
    that could be misunderstood as being controle characters by the other side.

    This has been woking fine for a long time. however, during SAIX's tinkering,
    they managed to get their PPP gateways to not ignore controle characters
    coming in as part of IP packets, as they should be doing.

    What was going wrong was that some part of the DNS query must have been seen
    as some arb. controle character. The machine then handled the packet
    incorrectly, and it never reached the NS it was meant for.

    To fix this, just remove asyncmap 0 from your config file. This gives a
    slight performance hit, but with the wonderful resourcefullness of some
    ISPs, what can you do...

    Origional message follows:

    This gets a 10.0 on my weird-o-meter.

    I have a FreeBSD 4.7-RELEASE machine sitting at a client which dials in and
    collects their mail via POP3, and sends outgoing mail via a smarthost which
    points to an SMTP server at their ISP.

    This machine has worked fine since late last year, but started giving a
    strange problem this week.

    When connected to their ISP, SAIX, the machine can ping any live internet IP
    and it can traceroute to anywhere, but, it can not talk to any DNS server.
    Any traffic to port 53 UDP simply seems to dissapear.

    The same with firewalling enabled as normal, or even with ipfw add 1 allow
    ip from any to any

    When connected to any other ISP we have tried dialing, all works perfectly.
    When dialed from another FreeBSD box with the same username/password, the
    SAIX connection works perfectly.

    Yet, this single machine absolutely flat out refuses to talk to any name
    server while connected to SAIX, firewalling, no firewalling, no difference.

    I have tried running tcpdump -i ppp0 udp port 53 in an attempt at capturing
    these packets, nothing, I also looked at rl0 just for interest's sake,
    nothing.

    I have run out of ideas, what am I missing?

    PS: Please CC me in the reply, I get so much list mail I might miss a reply
    there. 

    -- 
Willie Viljoen
Freelance IT Consultant
214 Paul Kruger Avenue, Universitas
Bloemfontein
9321
South Africa
+27 51 522 15 60
+27 82 404 03 27 (mobile)
will@unfoldings.net
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  • Next message: Konrad Heuer: "Re: [NEWBIE] Using external SMTP-Server for mail"

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