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RE: discovering network layout at layer2
From: Brian_Peterson () Dell com
Date: Wed, 11 Feb 2004 16:45:14 -0600

Cisco's layer 2 discovery protocol is CDP, which is enabled by default. You
can either find a tool to enumerate devices using CDP or you can write a
script to ssh, rsh, or telnet in and issue the 'sh cdp neighbor detail'
command to learn about all directly connected layer 2 devices, then issue
the same command on those devices, etc., until you have it all mapped out.

-----Original Message-----
From: Dev [mailto:u02113 () cs unipune ernet in] 
Sent: Friday, February 06, 2004 10:27 AM
To: pen-test () securityfocus com
Subject: discovering network layout at layer2

Hello ppl,

I am new to this list. Plz redirect me to another list if this is not the
appropriate list to post to this query. 

Having read the phrack article "Fun with the spanning tree protocol", I was
wondering as to how i could use some layer2 protocols to my advantage to
discover the network layout of my campus network (at layer 2).

Additionally, all equipment is CISCO.

Identification of my nearest switch is easily done by sniffing for STP BPDU
packets & i did receive the STP hello BPDU packets on the user port that our
gateway was connected to. This kind of packet gives me the following

1) How many more STP -capable devices are there up to the root bridge (root
path cost)

2) The bridge & port ID & the root bridge & port ID.

Can somebody suggest how can i find out my network topology using this STP
protocol or some other layer2 protocol (CDP?? etc).

Devrat Mittal
u02113 () cs unipune ernet in
Department of computer Science
University of Pune


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