Some VTP Stuff

Here are some random things I labbed and debugged while configuring VTP.

Topology:

SW4 === SW3 === SW2

SW4 = VTP server
SW3 = VTP transparent
SW2 = VTP client

1) If VTP domain names don't match, then trunk cannot be negotiated:

This is on R3 and R4 while domain names were different, Trunk links were in "dynamic desirable" mode.

12:29:06: %DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Fa0/23 because of VTP domain mismatch.
12:29:06: %DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Fa0/24 because of VTP domain mismatch.

And on R4:

IPeCat4#show int trunk

So we statically configure trunking both sides (or change domain names...more on that later)

IPeCat3(config)#int rang f0/23 - 24
IPeCat3(config-if-range)#sw mo trunk
IPeCat3(config-if-range)#int po 34
% Command exited out of interface range and its sub-modes.
Not executing the command for second and later interfaces
IPeCat3(config-if)#sw mo trunk
IPeCat3(config-if)#

IPeCat3#show int trunk

Port Mode Encapsulation Status Native vlan
Po34 on 802.1q trunking 100

2) Debugging VTP

IPeCat3#debug sw-?
sw-ip-admission sw-vlan

IPeCat3#debug sw-vlan ?
badpmcookies vlan manager incidents of bad PM (Port Manager) cookies
cfg-vlan config vlan
events vlan manager events
ifs vlan manager ifs error tests
management vlan manager management of internal vlans
mapping vlan mapping
notification vlan manager notifications
packets vlan manager packets
redundancy VTP VLAN redundancy
registries vlan manager registries
vtp vtp protocol debugging

IPeCat3#debug sw-vlan vtp ?
events vtp events
packets vtp packets
pruning vtp pruning events
redundancy vtp redundancy
xmit vtp packets transmitted

3) Domain must match for vtp packets to pass through

IPeCat4(config)#vlan 420
IPeCat4(config-vlan)#exit

SW3 denies it:

IPeCat3#
12:34:48: VTP LOG RUNTIME: Dropping packet received on trunk Po34 - not in domain ipexpert
12:34:48: VTP LOG RUNTIME: Dropping packet received on trunk Po34 - not in domain ipexpert
IPeCat3#

SW2 does not know about the VLAN now:

IPeCat2#show vlan id 420
VLAN id 420 not found in current VLAN database
IPeCat2#

We must change domain name on SW3:

IPeCat3(config)#vtp domain ipexpert
Changing VTP domain name from wrong to ipexpert
IPeCat3#show vtp sta | inc Domain
VTP Domain Name : ipexpert
IPeCat3#

(This takes while)

12:37:55: VTP LOG RUNTIME: Relaying packet received on trunk Po34 - in TRANSPARENT MODE (nc = false)
12:37:55: VTP LOG RUNTIME: Relaying packet received on trunk Po34 - in TRANSPARENT MODE (nc = false)

SW2 has the vlan now:

IPeCat2#show vlan | inc 420
420 VLAN0420 active
420 enet 100420 1500 - - - - - 0 0
IPeCat2#