CDPSnarf is a network sniffer exclusively written to
extract information from CDP packets. It provides all
the information a "show cdp neighbors detail" command
would return on a Cisco router and even more.

A feature list follows:
  Time intervals between CDP advertisements
  Source MAC address
  CDP Version
  TTL
  Checksum
  Device ID
  Software version
  Platform
  Addresses
  Port ID
  Capabilities
  Duplex
  Save packets in PCAP dump file format
  Read packets from PCAP dump files
  Debugging information (using the "-d" flag)
  Tested with IPv4 and IPv6

Source: https://github.com/Zapotek/cdpsnarf