VLAN Questions

[azev]

what would be the correct anwswer to this question:

Which VLAN's are allowed over a new trunk link that is configured on a IOS based switch ?

a. All defined VLAN are allowed on the trunk by default
b. Each VLAN, or VLAN range, that is specified with the switchport mode command
c. Each VLAN, or VLAN range, that is specified with the vtp domain command
d. Each VLAN, or VLAN range, that is specified with the vlan database command

I think A is the correct answer. becase you need type " switchport trunk allowed vlan" to limit or allow which vlan data can go over the trunk.

what do you guys think ?

 

[Slvrtg277]

I don't think A is right, because you have to specify which VLAN's are trunked before they are trunked. Just because a VLAN is defined doesn't mean it's allowed over the trunk.

B doesn't sound right because the switchport mode command specifies whether or not the link is a trunk, access, etc.

C doesn't sound right because the vtp domain command specifies which VTP domain the switch will belong to/transparent, etc.

D seems like the only viable answer, but I don't like it either. I guess maybe it assumes you are using VTP and the trunking is already taken care of before you add the vlan to the database maybe?


I hate these type of questions.

 

[randal]

I'm pretty sure it's A ... I had to look this up a couple weeks ago because I was arguing with a coworker about it.

edit - yea, just found it: "By default, a trunk port allows all VLANs through the trunk as shown in Example 4-8" LAN Switching Fundamentals - CiscoPress

 

[nightowl]

Yes it is A. By default a trunk port will allow all vlans to traverse the trunk (1-1005 or 1-4096).

 

[spidey07]

Originally posted by: nightowl
Yes it is A. By default a trunk port will allow all vlans to traverse the trunk (1-1005 or 1-4096).

not quite true.

on a CatOS switch you have to define what VLANs are allowed on the trunk with the set trunk command.

IMHO, this is a much better approach because you don't want to trunk every vlan everywhere - its just really poor design. You really should prune every VLAN from a trunk unless that vlan is actually needed on the trunk. Or better yet, just use layer 3 switching instead.

 

[Slvrtg277]

Originally posted by: spidey07

Originally posted by: nightowl
Yes it is A. By default a trunk port will allow all vlans to traverse the trunk (1-1005 or 1-4096).

not quite true.

on a CatOS switch you have to define what VLANs are allowed on the trunk with the set trunk command.

IMHO, this is a much better approach because you don't want to trunk every vlan everywhere - its just really poor design. You really should prune every VLAN from a trunk unless that vlan is actually needed on the trunk. Or better yet, just use layer 3 switching instead.

Agreed. Hence my earlier post. Why have all those spanning-tree instances and un-needed traffic?

spidey knows his stuff.