Example 726 Monitoring VTP Messages

sw3512XL(config)#service timestamps debug datetime localtime msec sw3512XL(config)#service timestamps log datetime localtime msec sw3512XL(config)#end sw3512XL#clear counters sw3512XL#clear log sw3512xl#debug sw-vlan vtp events

vtp events debugging is on

sw3512xl#configure terminal

sw3512xl(config)#interface fastethernet 0/1

sw3512xl(config-if)#port monitor fastethernet 0/11


sw3512xl#show port monitor

Monitor Port Port Being Monitored

FastEthernet0/1 FastEthernet0/11

sw3512xl#show log

Syslog logging: enabled (0 messages dropped, 0 flushes, 0 overruns)

Console logging: level debugging, 332 messages logged

Monitor logging: level debugging, 0 messages logged

Trap logging: level informational, 67 message lines logged

File logging: disabled

Buffer logging: level debugging, 332 messages logged

Log Buffer (4096 bytes):

ARENT MODE (nc = false)

VTP LOG RUNTIME: Relaying packet received on trunk Fa0/11 -

in TRANSPARENT MODE (nc = false)

sw3512xl#show vlan brief

VLAN Name Status Ports

1 default active Fa0/1, Fa0/3,


Fa0/5, Fa0/6,

Fa0/7, Fa0/8,

Fa0/9, Fa0/10,

Gi0/1, Gi0/2

10 vlan10 active

1002 fddi-default

1003 token-ring-default

1004 fddinet-default

1005 trnet-default active Fa0/12, Fa0/12

active active active active

VTP messages always travel over the default VLAN. Figure 7-6 is an example of a VTP summary advert isem ent. Re fer to Table 7-5 for VTP header information and Table 7-6 for VTP message types.

The Summary Pane and DLC header of Figure 7-6 show the destination MAC address of 01000CCCCCCC. LLC uses AA to indicate that the SNAP header follows. The SNAP header includes Cisco as a vendor/OUI with a type of 2003 for VTP. The VTP header includes such fields as the protocol version, a message type of 0x01 for the summary advertisement, the management domain size and name, any padding, the configuration revision number, the updater idpntity IP ad dress, a ti me stamp, and a n MD5 digest h/sh value .

Table 7-6. VTP Message Types



Summary advert iseme nrs

Issued by servers and clients every 5 minutes.

If higher revision number, the receiving switch issues an advertisement request for the new VLAN information.

Fidlds include version, type, number of sub net advertisement messages, domain name length, managed domain name, configuration revision number, updater identityo u pdate tim e stamp, a nd MD5 digest.

Subset advertisements

Issued due to changes such as creating, suspending, activating, renaming, or changing the MTU of a VLAN.

One or more advertisements depending on how many VLANs.

Advertise ment requests

W hen devine hears of higher revision number, it asks for it.

VTP join messages

For pruning.

The command show vtp statistics is used to track VTP activity, as you can verify in Example 727. You can com leaae the stati sties to the VTP meshaq e types i n Tabl e 77-6 to sne how man y of1 each message type have been sent. Keep an eye o n the "Numee r of1 comfig diqest errors"; enless wou have other transmit-type errors, it is a good indication that someone is trying to hack in and corrupt things.

Revision numbers are critical in the VTP server mode, but not used in the transparent mode. They range from 0 to 2,14r,483,648. The set vtp domain name command is a quick way to reset the counter to 0 without having to make too many changes. Remember this when you art adding new switches into your environment.

The same version of VTP is needed throughout the management domain. VTP version 2 includes such functionality as Token Ring and various consistency checks. You can turn on version 2 with theset vtp v2 enable command and verify it with show vtp domain.

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