Trunking and protocols

[Sulaiman Ejaz]

Hello,

VTP(vlan trunking protocol) is a layer 2 protocol that tranfers the vlan information between switches, my question is what is trunking and which protocol is responsible for trunking?

[Peter Paluch · Accepted solution]

Hi Sulaiman,

Trunking, in Cisco's vocabulary, is a way of interconnecting switches with a single link that carries traffic in multiple VLANs. While VTP makes sure these switches have the same set of VLANs, their numbers, names and states, trunking  itself allows you to extend the reach of these VLANs between these switches so that stations in the same VLAN connected to any of these switches form a single, contiguous broadcast domain.

Because frames carried by a trunk may be originated in several different VLANs, there must be a way of distinguishing which VLAN does each frame belong to. There are two protocols used for this - Cisco's old proprietary Inter Switch Link (ISL) and the open IEEE 802.1Q. Without going into much detail, I suggest you read the following document about both of them.

http://www.cisco.com/en/US/tech/tk389/tk689/technologies_tech_note09186a0080094665.shtml

Best regards,

Peter

[Sulaiman Ejaz]

Thankyou peter, your answer always help me a lot!

regards,

Muhammad Sulaiman Ejaz.