VTP Pruning Question

From: Michael Zuo (mzuo@ixiacom.com)
Date: Thu Dec 07 2006 - 15:48:14 ART

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Hi Group,

Did not hear from anyone on this. Just thought I posted again because I
am dying to know :-) . if you have a doc link explaining this, that
would be great (the doc command reference only shows an example without
explanation)

I enabled VTP pruning between SW1 and SW2 where SW2 is the server (see
below). SW2 has ports in VLAN 2 and 3 and SW1 has ports in VLAN 2 and
4. shouldn't the VTP pruning allow only VLAN 1 and 2 to go over the
trunks since VLAN 2 is the only VLAN used by both switches? Why does my
output shows that SW2 allows 1,2,4 and SW1 allows 1 and 3?

Thanks in advance....

SW2(config)#do sh vlan

VLAN Name Status Ports

---- -------------------------------- ---------

-------------------------------

1 default active Fa0/1, Fa0/4, Fa0/5,

Fa0/6

Fa0/7, Fa0/8, Fa0/9,
Fa0/10

Fa0/11, Fa0/12, Fa0/16,

Fa0/17

Fa0/18, Fa0/19, Fa0/20,

Fa0/21

Fa0/22, Fa0/23, Fa0/24,

Gi0/1

Gi0/2

2 VLAN0002 active Fa0/2

3 VLAN0003 active Fa0/3

4 VLAN0004 active

26 VLAN0026 active

43 VLAN0043 active

55 VLAN0055 active

62 VLAN0062 active

1002 fddi-default act/unsup

1003 token-ring-default act/unsup

1004 fddinet-default act/unsup

1005 trnet-default act/unsup

VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1

Trans2

---- ----- ---------- ----- ------ ------ -------- ---- -------- ------

------

SW2(config)#do sh int trun

Port Mode Encapsulation Status Native vlan

Fa0/13 on 802.1q trunking 1

Fa0/14 on 802.1q trunking 1

Fa0/15 desirable n-802.1q trunking 1

Port Vlans allowed on trunk

Fa0/13 1-4094

Fa0/14 1-4094

Fa0/15 1-4094

Port Vlans allowed and active in management domain

Fa0/13 1-4,26,43,55,62

Fa0/14 1-4,26,43,55,62

Fa0/15 1-4,26,43,55,62

Port Vlans in spanning tree forwarding state and not pruned

Fa0/13 1-2,4

Fa0/14 none

Fa0/15 none

SW2(config)#do sh vtp st

VTP Version : 2

Configuration Revision : 3

Maximum VLANs supported locally : 1005

Number of existing VLANs : 12

VTP Operating Mode : Server

VTP Domain Name : CCIE

VTP Pruning Mode : Enabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0xA2 0xCA 0x34 0x8F 0x26 0x52 0xD2

0x1F

Configuration last modified by 0.0.0.0 at 3-1-93 00:11:44

Local updater ID is 0.0.0.0 (no valid interface found)

SW2(config)#

SW1(config)#do sh vlan