CCIE Pursuit Blog

September 25, 2007

VTP: Local updater ID on VTP Transparent Switches

Okay, this is the last post of the VTP Local updater ID trilogy.  I promise.  🙂

Here are the first two posts:

VTP: Which VTP Server Generated The Most Recent Update?

VTP: More On The Local updater ID

This last post concerns the behavior of the Local updater ID on VTP transparent switches.  At first blush, it looks like this feature should not appear on a transparent switch.  If you have a transparent switch, then the updates will always be local, but you can still use the Local updater ID feature:

sw3(config)#do sh vtp status
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 5
VTP Operating Mode              : Transparent
VTP Domain Name                 : CCIE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x13 0x23 0x62 0x16 0x83 0xCD 0x50 0xEC
Configuration last modified by 0.0.0.0 at 9-25-07 09:41:32

Let’s add an IP address and a VLAN to the switch:
sw3(config)#int lo0
sw3(config-if)#ip add 10.0.0.3 255.255.255.255
sw3(config-if)#vlan 666
sw3(config-vlan)#name VLAN_OF_THE_BEAST
sw3(config-vlan)#exit

sw3(config)#do sh vtp statu
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 6
VTP Operating Mode              : Transparent
VTP Domain Name                 : CCIE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x04 0x4E 0xE9 0xBF 0x79 0x81 0x44 0x8F
Configuration last modified by 10.0.0.3 at 9-25-07 09:41:32

sw3(config)#do sh vlan id 666

VLAN Name                             Status    Ports
—- ——————————– ——— ——————————-
666  VLAN_OF_THE_BEAST                active    Fa0/19, Fa0/20, Fa0/21

Notice that you do not see the “Local updater ID is x.x.x.x” line in the “show vtp status” output when the switch is in transparent mode.  BUT you do see that the switch will record the IP address of the switch that updated the VLAN database (which will always be the local switch when the switch is in VTP transparent mode).  Notice that it follows the same rules (first IP address, lowest vlan ip address, vtp interface, etc) as the client/server switches:

sw3(config-if)#int vlan 666
sw3(config-if)#ip add 6.6.6.3 255.255.255.0
sw3(config-if)#do sh ip int br | e ass
Interface              IP-Address      OK? Method Status                Protocol
Vlan666                6.6.6.3         YES manual up                    up
Loopback0              10.0.0.3        YES manual up                    up
sw3(config-if)#do sh vtp statu
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 6
VTP Operating Mode              : Transparent
VTP Domain Name                 : CCIE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x04 0x4E 0xE9 0xBF 0x79 0x81 0x44 0x8F
Configuration last modified by 10.0.0.3 at 9-25-07 09:41:32 <-last update used lo0 IP address

Add another VLAN:
sw3(config-if)#vlan 665
sw3(config-vlan)#name VLAN_OF_THE_NEIGHBOR_OF_THE_BEAST
sw3(config-vlan)#exit
sw3(config)#do sh vtp statu
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 7
VTP Operating Mode              : Transparent
VTP Domain Name                 : CCIE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x9A 0x6E 0x3A 0xCB 0x5F 0x43 0xC9 0xF7
Configuration last modified by 6.6.6.3 at 9-25-07 09:41:32 <-now using SWI vlan 665 address

We can also manually set the Local updater ID:
sw3(config)#vtp interface lo0 only
sw3(config)#no vlan 666
sw3(config)#do sh vtp status
VTP Version                     : 2
Configuration Revision          : 0
Maximum VLANs supported locally : 1005
Number of existing VLANs        : 6
VTP Operating Mode              : Transparent
VTP Domain Name                 : CCIE
VTP Pruning Mode                : Disabled
VTP V2 Mode                     : Disabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x04 0x4E 0xE9 0xBF 0x79 0x81 0x44 0x8F
Configuration last modified by 10.0.0.3 at 9-25-07 09:41:32 <- lo0 IP address (mandatory)

So even though it’s pretty unneeded, you CAN use the Local updater ID with VTP transparent switches.  This is probably due to either some overlooked code in IOS or to be able to maintain Local update ID settings when switching between VTP modes.

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