Cisco Discovery Protocol (CDP)

The Cisco Discovery Protocol (CDP) periodically sends layer-2 "beacons" on each port of Ethernet and ATM switches, announcing port capabilities and names.

• Overview
• CDP Monitor
• LCDP: Linux implementation, includes pointers to frame format
• CDP Version 2

To listen to CDP packets with snoop or tcpdump:

snoop -x 0 -v ether host  01:00:0c:cc:cc:cc

CDP packets are typically sent once per minute.

CDP is assigned the Cisco HDLC protocol type value 0x2000. A Cisco-proprietary SNAP value enumerates HDLC protocol type values so CDP can run on all media that support SNAP, such as LAN media, Frame Relay, and ATM.

The SNAP format is as follows: LLC = 0xAAAA03; Org ID = 0x00000C; HDLC protocol type = 0x2000

CDP sends packets on LANs using the multicast address 0100.0CCC.CCCC.

cepsr-7-1.net.columbia.edu      A       128.59.16.250 0:3:6b:29:63:ff

ETHER:  ----- Ether Header -----
ETHER:  
ETHER:  Packet 1 arrived at 21:59:23.48
ETHER:  Packet size = 250 bytes
ETHER:  Destination = 1:0:c:cc:cc:cc, (multicast)
ETHER:  Source      = 0:5:5f:3c:dc:48, 
ETHER:  IEEE 802.3 length = 236 bytes
ETHER:  Ethertype = 2000 (Unknown)
ETHER:  


           0: 0100 0ccc cccc 0005 5f3c dc48 00ec aaaa    ........_<.H....
                                                 LCC                                                              
          16: 0300 000c 2000 02b4 16ca 0001 001a 464f    .... .........FO
                        EtherV 180s    T=1  L=22
          32: 5830 3431 3731 3431 3628 6365 7073 722d    X04171416(cepsr-
          48: 372d 3129 0002 0011 0000 0001 0101 cc00    7-1)............
                        T=2  L=13
          64: 0480 3b10 fa00 0300 0736 2f39 0004 0008    ..;......6/9....
                          T=3  L=4  6  /  9 T=4  L=4
          80: 0000 000a 0005 006e 5753 2d43 3430 3036    .......nWS-C4006
           0x8 0x2      T=5  L=107
          96: 2053 6f66 7477 6172 652c 2056 6572 7369     Software, Versi
         112: 6f6e 204d 6370 5357 3a20 352e 3528 3130    on McpSW: 5.5(10
         128: 2e30 2920 4e6d 7053 573a 2035 2e35 2831    .0) NmpSW: 5.5(1
         144: 3029 0a43 6f70 7972 6967 6874 2028 6329    0).Copyright (c)
         160: 2031 3939 352d 3230 3031 2062 7920 4369     1995-2001 by Ci
         176: 7363 6f20 5379 7374 656d 732c 2049 6e63    sco Systems, Inc
         192: 2e0a 0006 000c 5753 2d43 3430 3036 0009    ......WS-C4006..
                   T=6  L=8  W S  - C  4 0  0 6  T=9
         208: 0017 436f 6c75 6d62 6961 5f55 6e69 7665    ..Columbia_Unive
              L=19
         224: 7273 6974 7900 0a00 0600 1000 0b00 0501    rsity...........
                          T=10 L=2       T=11 L=1
         240: 0012 0005 0000 1300 0500                   ..........
              T=18 L=1    T=19 L=1

Last updated by Henning Schulzrinne