Code Red, ARP and YOU!!

From: Mike Brown (
Date: 08/06/01

Message-ID: <>
Date: Mon, 06 Aug 2001 00:29:14 -0400
From: Mike Brown <>
Subject: Code Red, ARP and YOU!!

This may be obvious to many, but it stumped me for 5 or 10 mins, so
allow me to share.
     Today after I got home from work I looked at my cable modem and
itís data light was blinking like there was no tomorrow. My first
thought, OMG I finally got hacked! And Iím part of a DDoS attack, Wohoo
for me! ďAbout timeĒ I thought, now the fun part. How did they do it?
Well sadly it wasnít to be. After Much looking I found that no programs
where running that shouldnít and that there where no connection that
didnít belong. So I fired up Ethereal and had it listen for 17 seconds.
In those 17 seconds I recorded 474 packets coming and going from my pc.
The fun part is 451 of them are ARP broadcasts. And all of them are
coming from just 2 IPís.
     My theory is that because on a cable modem network no one ever
needs to contact any other host besides the router none of the hosts
know the other IPís thus the flood of ARP requests.
     Now the useful part. There was some talk about the moral
implications of scanning others servers, especially from the ISPís side.
They donít want to piss anyone off but they donít want to host the worm
of the day. Well the really passive way to detect the Code Red worm of
any version is to look for the exponential growth in ARP traffic on your
     Now on my network the two offending IPís are and judging from the last octet they could be routers but the
basic idea holds true, just look on the other side of the routers.
     Now if Iíve missed something incredibly obvious (besides my
spelling and mind) please pardon me, Mike the lowly Tier one tech
support guy. But I think Iíve got something here. Is there any other
reason to see dozens of ARP requests a second coming from the same host?

- Mike