Trunk link

hello

through what port and with what cables would you normaly connect 2 or more switches with a trunk link?

some switches have a dedicated A and B Gigabit ports but what if you have an old 2900 XL switch?

thanks
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Comments

BubbaJ

As long as it is a 100 Mbps port, it will work, although some 2900 series switches have problems with trunking.

exkor5000

thanks

garv221

Alot of the time trunking between different series switches requires different encapsulation methods.

exkor5000

i assume this would depend upon the IOS version in use

BubbaJ

exkor5000 wrote:

i assume this would depend upon the IOS version in use

Not really, it depends more on the model of switch used. I believe that the switch model you are talking about won't do 802.1Q, only ISL. There are some models of 2900 switches that only do ISL, some that only do 802.1Q, and some that do both. You will have to do some research at cisco.com to determine what your particular model will or won't do.

mp3spy

Yea, and if they're layer 2 switches you need a router to pass data to different vlans on different switches. Though, you still a trunk link :P

wildfire

Not really, it depends more on the model of switch used. I believe that the switch model you are talking about won't do 802.1Q, only ISL. There are some models of 2900 switches that only do ISL, some that only do 802.1Q, and some that do both. You will have to do some research at cisco.com to determine what your particular model will or won't do.

Yeah and I found this one out the hard way, a 2950 and a 5000 running an older CATOS image, 2950=802.1Q only, 5000 Supervisor II = ISL only, result = failure.

you live and learn.

Danman32

mp3spy wrote:

Yea, and if they're layer 2 switches you need a router to pass data to different vlans on different switches. Though, you still a trunk link :P

It doesn't matter if the VLans are on the same or different switches, packets still have to be routed to go between them.

And you don't have to have a trunk to have the packets routed between vlans. You could have a separate link to the router from each VLAN.

mp3spy

Danman32 wrote:

mp3spy wrote:

Yea, and if they're layer 2 switches you need a router to pass data to different vlans on different switches. Though, you still a trunk link :P

It doesn't matter if the VLans are on the same or different switches, packets still have to be routed to go between them.

And you don't have to have a trunk to have the packets routed between vlans. You could have a separate link to the router from each VLAN.

Correct. However, without a trunk it hauls down bandwidth and produces uneccessary packet floods. Plus, you want every switch to learn about all VLANS in the LAN. You need to break up the broadcast domains as much as possible unless your budget is not of any concern.

Cauthon

mp3spy wrote:

Correct. However, without a trunk it hauls down bandwidth and produces uneccessary packet floods. Plus, you want every switch to learn about all VLANS in the LAN. You need to break up the broadcast domains as much as possible unless your budget is not of any concern.

I've read this post several times and I really can't grasp the point you're trying to make.

Not using a trunk port for inter-VLAN routing doesn't "Haul Down Bandwidth", it just requires more ports on the router and more ports on the switch.

I don't know if there's such a thing as a 'necessary packet flood', but if you're trying to eliminate broadcast packet storms you need to use STP not a trunk port.

If you want every switch in a switching fabric to learn about VLANs through a central configuration you need to use VTP (VLAN Trunk Protocol), which ironically has nothing to do with VLAN trunking, but rather the exchange of VLAN configuration via a Layer 2 broadcast.

The sole purpose of a trunk port is to carry frames from multiple VLANs to other devices using a single port. It accomplishes this by adding a VLAN tag to each frame to identify the originating VLAN. If a switch port isn't a trunk port, then it will be a member of a single VLAN and will only carry traffic for that VLAN.

Mike

Danman32

Thanks Cauthon, I thought I might be missing something. If anything, using a port as trunk as opposed to using multiple ports of equal raw bandwidth, one for each VLAN would reduced bandwidth, since with the trunk you are sharing the bandwidth amongst multiple broadcast domains.