Can't see some traffic in CDP packet using tcpdump
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)
Subscriber exclusive content
A Red Hat subscription provides unlimited access to our knowledgebase, tools, and much more.