Re: [Full-Disclosure] DHCP Flood on inside network. HELP!!

From: Gregory Gilliss (ggilliss_at_netpublishing.com)
Date: 10/12/04

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    To: Eddie <EddieS@softhome.net>
Date: Mon, 11 Oct 2004 23:53:18 -0700

    Sounds like someone discovered the DHCP discover flood trick and set it
    to work on you. A little packet filtering kung fu on your part ought to be
    sufficient to prevent it happening again.

    -- Greg

    On or about 2004.10.11 22:00:07 +0000, Eddie (EddieS@softhome.net) said:

    > I don't have much information on this yet, I am driving down to the office now to pull an all nighter. I figured I would toss this out to the list and see if anyone has any
    > idea. This is just info from what I can get from talking to people and what little time I can get on the network before it goes down.
    >
    > Starting 2 days ago, I discovered the PIX 515 was locked hard. It seems to be random, but around every 15-30 minutes something floods the network hard for a few
    > minutes. Broadcast flood too. This is a small network with 30 workstations and 5 servers (Linux and SCO, no Wins). It overloads the Extreme switches and I see pdu (or
    > something like that, not udp tho) errors on about every port.
    > The Pix 515 overloads and is having issues, but I did see it say something about ARP problems when I could get to the syslog for more info. I looked up the error
    > number and it said it could be ARP poisoning. Not sure what would do that.
    >
    > In the syslog of the DHCP server, I see thousands of DHCP DISCOVER request(and the REPLAY request from the server, a Linux box). It looks like one client on the
    > network (I have seen this both from XP and Win98) will send 100+ DISCOVER request a second swamping the network. Not always DISCOVER too.
    > That will go on for a few minutes, then all is well. Then another computer will do the same thing.
    >
    > This is quickly overloading things and I am getting IRQ busy and overload errors on some of the servers.
    >
    > What should I look for. I have never seen something like this before.
    >
    > Thanks
    > -Eddie
    >
    >
    >
    >
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    -- 
Gregory A. Gilliss, CISSP                              E-mail: greg@gilliss.com
Computer Security                             WWW: http://www.gilliss.com/greg/
PGP Key fingerprint 2F 0B 70 AE 5F 8E 71 7A 2D 86 52 BA B7 83 D9 B4 14 0E 8C A3
_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html
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