Posted on 2009-12-22
Last Modified: 2012-05-08

I need some explanation on trunking.

My setup has 6509 connected to 2 X cat 4006 switches.
p01 ,p02 are enabled for trunking.And module 4/25,4/29,4/31 are enable for 802.1q trunks.

Similiarly some ports modules 6,7,9 are all enabled for trunking

From show trunk interface Iam able to see the vlans it is carrying.

why we have two  or 3 trunks on same module?
where does this trunk get terminated?I believe on switch 4006 ?Is my understanding right?
Please reply ASAP.


Question by:phoenix26
    LVL 4

    Assisted Solution

    You can do a 'show cdp neigh' to see connected devices / virtual servers.
    if unable to do so, Pls post configs to look into.
    LVL 21

    Accepted Solution

    Trunks are usually used between switches for redundnacy and bandwidth increasing purposes. If one link fails the connection stays up on the other links in the trunk. They can also be run to servers if the server supports them for the same reasons.

    Is that what you are asking?

    Author Comment



    Thanks for the answers.

    I believe trunks are used for transferring vlans from one switch to another.

    Now u say it is for redundancy and bandwidth increasing.
    confusing.can you elobarate?

    Can any one advice me on the role of these TRUNKING PORTS IN SPANNING TREE PROTCOL? AND STP CONVERGENCE ?

    LVL 21

    Assisted Solution

    Yes trunks are used for connecting VLANs between switches. I think Cisco uses the term trunking to imply VLAN tagging. VLAN tagging is how switches communicate VLAN information for multiple VLANs over the same link.

    If you combine multiple ports together as a single connection between switches that is also a trunk. That is where I was making the point about redundancy, etc. because there is more than one link in use between the switches.

    If you are using multiple links between switches as a trunk then spanning tree looks at the whole group as a single connection for its purposes. If it is not a trunk then spanning tree would block on all of the links except one.

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