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vlan trunking help.

Hi

If I have switch (switch 3) in a network which only has vlan 2 and 3 listed in its vlan database. If I have atrunk link to other switches that have other vlans listed in their respective vlan databasese, would switch 3 forward those other vlans via its trunk link, even though the vlan's aren't listed in its database?

Thanks for any help.

Dan

1 ACCEPTED SOLUTION

Accepted Solutions

Re: vlan trunking help.

yes dan,

your VLAN information will travel through the trunk to the other switch even there is no same vlan on other switch...if you want to prevent that unnessesary information of VLAN travel through the switch then you have to configure the VLAN PRUNING...

you will get more idea about it from following link

this link will give you idea

http://www.cisco.com/warp/public/473/11.html

and this will usefull for configuration

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_4_2/config/vlans.htm#xtocid798016

remember to rate this post if it helps

regards

Devang

4 REPLIES

Re: vlan trunking help.

yes dan,

your VLAN information will travel through the trunk to the other switch even there is no same vlan on other switch...if you want to prevent that unnessesary information of VLAN travel through the switch then you have to configure the VLAN PRUNING...

you will get more idea about it from following link

this link will give you idea

http://www.cisco.com/warp/public/473/11.html

and this will usefull for configuration

http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_4_2/config/vlans.htm#xtocid798016

remember to rate this post if it helps

regards

Devang

Re: vlan trunking help.

dan its word VTP pruning

this is also good one

http://www.networknewz.com/2004/0317.html

rate the post if it helps

regards

Devang

Re: vlan trunking help.

Just to add that only broadcast , unknown unicast and multicast will travel to the other switch.

Vlad

Re: vlan trunking help.

Hello Dan,

I traffic for other vlans will travel to the other switch if the vlan is a native vlan (when using dot1q) or when its a broadcast.

Not all traffic will travel to the other switch.

Anyway, if you need to restric traffic there're 2 options:

switchport trunk allowed vlan {add | all | except | remove} vlan-list

or vtp pruning.

"VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices. Without VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all trunk links within a VTP domain even though receiving switches might discard them. VTP pruning is disabled by default."

Its always a good practice to only let the needed vlan to cross the trunk links.

HTH,

if it does, please rate this post.

Vlad

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