Re: What am I seeing?

From: Richard.Smithat_private
Date: Tue Oct 23 2001 - 10:35:22 PDT

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    A fraggle attack is not an ICMP based attack. It is UDP based. 
    Nevertheless, you should be filtering all reserved and RFC 1918 networks 
    at your borders. This would prevent UDP ECHO's from ever reaching your 
    internal hosts. The intent of the attacker seems to be to bring down your 
    /24 not any other external site. So they might redirect their attack at 
    your router if you filter their spoofed network. Then their attack might 
    not be as effective since it won't be amplified by your internal hosts, 
    but it might be annoying. If you have filtered their bogus source 
    ( and they continue to barrage your router you have no choice but 
    to work  with your upstream provider and track the source via ASN as 
    Valdis mentioned below. 
    If you need info on filtering the reserved and/or RFC 1918 networks or 
    hardening Cisco routers in general a good white paper is Bastion Routers 
    and you can find it on Phrack.
    Richard S Smith
    Sr Information Security Analyst
    Global Integrity a Division of Predictive Systems
    10/23/2001 12:29 PM
            To:     jkruser <jkruserat_private>
            cc:     incidentsat_private, focus-idsat_private
            Subject:        Re: What am I seeing?
    On Tue, 23 Oct 2001 11:38:36 EDT, jkruser said:
    > problem is...looks like, to me, that it is not coming from 
    > the ingress filtering will not stop it. Or am I missing something?
    > 79, 2001-10-23 02:57:31, 2000205, Possible Fraggle attack initiated,
    > MY.C.BLOCK.177, ,, , dstport=7&srcport=21497, 1
    The trick here is to remember that ingress filtering will *not* stop these
    packets (as you noted, they originate inside the filter).  What you need
    to do is find the packet that's being sent IN that's causing these 
    and ingress filter THAT.
    This is similar to stopping SMURF attacks (which consist of streams of
    ICMP Echo Reply packets) by configuring your routers to Do The Right
    Thing(*) with ICMP Echo *Request* packets....
    Systems Analyst
    (*) The Right Thing is documented in RFC2644 "Changing the Default for
    Directed Broadcast in Routers".  To summarize - routers should drop
    packets going to a subnet's broadcast address by default, and it should
    only be enabled if you know what you're doing....
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