Can't see some traffic in CDP packet using tcpdump

Solution Verified - Updated -

Issue

  • I can't see "Native VLAN" information in CDP packet when captured and viewed by tcpdump.
  • Some information is cut off when reading Cisco Discovery Protocol packets off the wire.
  • The following should include more fields like "Native VLAN" and "Duplex":
# tcpdump -vv -r cdp.cap | less
17:49:31.191283 CDPv2, ttl: 180s, checksum: 692 (unverified), length 443
        Device-ID (0x01), length: 34 bytes: 'switch.example.com'
        Version String (0x05), length: 264 bytes:
          Cisco IOS Software, Catalyst 4500 L3 Switch Software (cat4500e-IPBASEK9-M)
          Technical Support: http://www.cisco.com/techsupport
          Copyright (c) 1986-2011 by Cisco Systems, Inc.
          Compiled Thu 27-Jan-11 12:19 by prod_rel_team
        Platform (0x06), length: 15 bytes: 'cisco WS-C4900M'
        Address (0x02), length: 13 bytes: IPv4 (1) switch.example.com
        Port-ID (0x03), length: 18 bytes: 'GigabitEthernet0/1'
        Capability (0x04), length: 4 bytes: (0x00000029): Router, L2 Switch, IGMP snooping
        Prefixes (0x07), length: 5 bytes:  IPv4 Prefixes (1): 10.0.0.0/20
        VTP Management Domain (0x09), length: 0 byte: ''

Environment

  • Red Hat Enterprise Linux 6.5
  • tcpdump-4.0.0-3.20090921gitdf3cb4.2.el6
  • Network device sending Cisco Discovery Protocol (CDP)

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