by Cyrus Lok on Thursday, May 13, 2010 at 10:45pm

I do not like auto encapsulation and this is the problem of having backward compatibility….2950 does not support ISL anymore… 3550 still support both ISL as well as 802.1q. I will have to disable the auto encapsulation negotiation feature to hardcode my trunk ports as trunk.

Enter configuration commands, one per line. End with CNTL/Z.
3550-1(config)#int range fa0/1 – 2
3550-1(config-if-range)#switchport mode trunk
Command rejected: An interface whose trunk encapsulation is “Auto” can not be configured to “trunk” mode.
Command rejected: An interface whose trunk encapsulation is “Auto” can not be configured to “trunk” mode.

3550-1(config-if-range)#switchport trunk encapsulation dot1q

3550-1(config-if-range)#switchport mode trunk
3550-1(config-if-range)#
*Mar 1 00:34:28.539: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to down
*Mar 1 00:34:28.543: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to down
3550-1(config-if-range)#

3550-1#sh vlan brief

VLAN Name Status Ports
—- ——————————– ——— ——————————-
1 default active Fa0/3, Fa0/4, Fa0/5, Fa0/6
Fa0/7, Fa0/8, Fa0/9, Fa0/10
Fa0/11, Fa0/12, Fa0/13, Fa0/14
Fa0/15, Fa0/16, Fa0/17, Fa0/18
Fa0/19, Fa0/20, Fa0/21, Fa0/22
Fa0/23, Fa0/24, Gi0/1, Gi0/2

fa0/1 and 2 are trunks so not within vlan brief output. To verify further:

Port Mode Encapsulation Status Native vlan
Fa0/1 on 802.1q trunking 1
Fa0/2 on 802.1q trunking 1

Port Vlans allowed on trunk
Fa0/1 1-4094
Fa0/2 1-4094

Port Vlans allowed and active in management domain
Fa0/1 1
Fa0/2 1

Port Vlans in spanning tree forwarding state and not pruned
Fa0/1 1
Fa0/2 1

3550-1(config)#vtp mode server
3550-1(config)#vtp password cyrus
Setting device VLAN database password to cyrus
3550-1(config)#vtp version 2
3550-1(config)#vtp domain cyrus

3550-1 will be the vtp server.

Version 2 vs version 1:

1. Version 1 transparent mode will forward vlan database to another switch within the same domain whereas version 2 transparent mode will forward vlan database to another switch regardless of what domain.

2. Version 2 provides consistency checking of the vlan database, if the vtp is in client mode and a corrupted vlan database is found the client will send a bpdu requesting the correct database from server.

3. version 2 supports token ring vlan (i have only heard of it but have not ever used it.. obselete?)

4. version 2 supports unrecognised vtp message instead of dropping unrecognised vtp message the switch will still forward it.

Both version 1 and 2 do not support vlan numbering extension. Version 3 however supports vlan numbering extension.

Without extension vlan numbering from 2 to 1001, vlan 1 is the default cannot be deleted. vlan 1002 to 1005 are vlans that support legacy technologies and cannot be deleted.

from 1006 until 4096 are extension, at present moment if you want to use vlan numbering extension you got to put the vtp mode to transparent mode, and it’s not worth it… in transparent mode the database will not be shared among other switches and admin got to manually configures vlans which is a huge hassle in my opinion.