Re: ARP flooded

From: Moe Trin (ibuprofin_at_painkiller.example.tld)
Date: 09/28/05 

Date: Wed, 28 Sep 2005 14:50:59 -0500

In the Usenet newsgroup alt.computer.security, in article
<1127893312.178941.184320@f14g2000cwb.googlegroups.com>, TaranFX wrote:

>my network is under discreet attacks with ARP packets. bcoz of this my
>switch mac address table is flooding, i tried increasing table size but
>of no use.

ARP (RFC0826) is a local protocol only. The source of the attack is one
of your systems. Use any packet sniffer to identify the source - it's
the second field (bytes 7 to 12) in the Ethernet header, or the second
IP address in the ARP packet itself. Then go to your switch, and see
which wire that host is on - go to that host, and disconnect it and
dispose the user remains.

>How can i prevent ARP attack?

Depends on your O/S and the size of the network and the amount of work
you want to do. You can simply disable ARP - and use ARP tables which
list the MAC and IP addresses of every host on your local LAN. Or, you
can make an example of the current attacker - severed head on a pike at
the door should make others aware that this is not a good idea.

>How do they burst so much ARP? can anybody gimme a source code of ARP
>flooder so that i can study it and prevent it from happening.

>From RFC0826:

                            Abstract
 
   The implementation of protocol P on a sending host S decides,
   through protocol P's routing mechanism, that it wants to transmit
   to a target host T located some place on a connected piece of
   10Mbit Ethernet cable. To actually transmit the Ethernet packet
   a 48.bit Ethernet address must be generated. The addresses of
   hosts within protocol P are not always compatible with the
   corresponding Ethernet address (being different lengths or
   values). Presented here is a protocol that allows dynamic
   distribution of the information needed to build tables to
   translate an address A in protocol P's address space into a
   48.bit Ethernet address.

So, creating an ARP flood is as easy as trying to identify every address
on your LAN.

        Old guy

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