NAME

       cdp - cdp packet generator

SYNOPSIS

       cdp  -i  <interface>  [-v  -n  x  -l  x  -c c -r] [-D <string> -P <string> -L <string> -S <string> -F <ip
       address> -C <capabilities>]

DESCRIPTION

       This manual page documents briefly the cdp  command.   This  manual  page  was  written  for  the  Debian
       distribution because the original program does not have a manual page.

       CDP  is  a layer 2 protocol used by Cisco routers to discover each other on the same link (segment). This
       protocol is not routed and therefore this tool is just usefull in the local segment.

       CDP messages contain information about the sending Cisco router. These include the device ID  (hostname),
       port ID (which port was the sender), the platform running on, the software incl. version, what the box is
       capable of and which network address (IP address) the interface has. If not configured  otherwise,  Cisco
       routers  send these messages out every 30 seconds. In our case (ethernet), they are send to a special MAC
       address (01:00:0C:CC:CC:CC) and therefore are received from every Cisco router in the same segment. Other
       routers  store  the  data and hold it for a time defined in the message (the tool uses the maximum of 255
       seconds).

       Very interesting is, that Cisco IOS uses the device ID as key to find out if the received message  is  an
       update and the neighbor is already known or not. If the device ID is to long, this test seems to fail and
       you constantly fill up the routers memory.

       The CDP tool can be used in two different modi:

       The flood mode is used to send garbage CDP messages to the wire,  which  has  different  effects  to  the
       routers  depending on their IOS version. It is not tested very well, which version of IOS reacts in which
       way on which kind of Cisco hardware. So if you come across somthing, please report it.  IOS  11.1(1)  was
       tested and the router could match even long device id´s but rebooted after receiving three or four random
       device id names. Most other IOS versions just store the message and fill up the memory. When you  try  to
       debug CDP events, all IOS we tested crashed and reboot.

       To use CDP, you have to specify the ethernet interface you will be working on: -i eth0

       Everything else is optional.

       -v     verbose

       -n x   send x packets

       -l x   length of the device id string. Keep in mind, that the
              whole ethernet frame has to be smaller the 1514 bytes.
              The maximum length is therefore 1480 for the device id
              (default is 1400)

       -c c   fills the device id with the char 'c' (default is 'A')

       -r     makes the device id a random string of characters, which
              leads to no matching on the receiver Cisco and to memory fillup
              or crash

       Example:

       Hint: if you want to flood the routers completly, start two processes of cdp with different sizes. One of
       them running on full size (1480) to fill up the major part of the memory and another to fill up the  rest
       with a length of 10 octets.

       The  second  mode for CDP is spoofing. You can enable this mode with the command line option -m 1. It has
       no actuall use for attacking router and is mostly targeted fro social engineering or just to confuse  the
       local  administrator. It is used to send out 100% valid CDP infromation packets which look like generated
       by other Cisco routers. Here, you can specify any part of a CDP message yourself.

       -i <interface> ethernet interface

       -v                     verbose

       -D <string>            device id string

       -P <string>            port id string

       -L <string>            platform string

       -S <string>            software string

       -F <ip address>        ip address of the interface

       -C <capabilities>      the capabilities of the device you are claiming to be:
                     R - Router, T - Trans Bridge, B - Source Route Bridge,
                     S - Switch, H - Host, I - IGMP, r - Repeater
                     Combine the letters to a string: RI means Router and IGMP

       Example:

       Which results on the cisco router in the following information:

       cisco#sh cdp neig detail

       -------------------------

       Device ID: Linuxfirewall

       Entry address(es):

       IP address: 10.1.1.1

       Platform: Intel,  Capabilities: Router

       Interface: Ethernet0,  Port ID (outgoing port): Ethernet0

       Holdtime : 238 sec

       Version :

       Linux vince 2.4.18-686 #1 Sun Apr 14 11:32:47 EST 2002 i686 unknown unknown GNU/Linux

AUTHOR

       This manual page was written by Vince Mulhollon <vlm@debian.org>, for the Debian  GNU/Linux  system  (but
       may be used by others).

                                                 January 1, 2003                                          CDP(1)