What in the difference in Port Channel and just a regular trunk link Interface?

Answered Question
Nov 22nd, 2009

Can anyone help with this easy answer?  In lehmans terms would be nice

Correct Answer by Jon Marshall about 7 years 2 months ago

cisco_himg wrote:

Ok cool. they all come back to the backbone on a Gig switch. so i guess since there are two channels, it will be 2 Gig connections coming back to me, correct?

If there are 2 physical links in each channel and the physical links are 1Gbps each then yes your portchannel is 2Gbps.

Jon

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Reza Sharifi Sun, 11/22/2009 - 18:57

With PortChannel or what is commonly referred to as 802.1ad link aggregation, you aggregate multiple links together.  For example, you aggregate multiple 1Gig or 10Gig interfaces together to have access to more bandwidth. The Maximum number of links that you can bundle together is 8.

A regular trunk link is a link that carries multiple VLANs.

HTH

Reza

Leo Laohoo Sun, 11/22/2009 - 20:00

Trunk link is just a single line that carry one or more VLANs.  It's called "trunk" because it was based on the same theory that of the large phone cables called "trunks".


Bundle up two to eight trunk lines and it's what is called as an Etherchannel.  There are two types of port etherchannel:  FastEtherchannel or GigabitEtherchannel.

Jon Marshall Mon, 11/23/2009 - 02:19

cisco_himg wrote:

Can anyone help with this easy answer?  In lehmans terms would be nice

Trunk link is, as Leo said, a single link usually between 2 switches that carries the traffic of multiple vlans.

A portchannel is a number of links, usually between switches, that are bundled together and treated as one single link by STP (Spanning tree). Because it is treated as one single link even though there are multiple physical links in th bundle none of the indiviual physical links are blocked by STP. This means you can have increased throughput but just as importantly if one of the physical links fails there is no STP reconvergence.

A portchannel can be a bundle of links that are all in the same vlan or it can be a bundle of links that are all trunk links. It can't be a combination of both.

Jon

cisco_himg Mon, 11/23/2009 - 09:17

Thanks guys!

How can i tell the speed of the port Channel compared to my regular trunk links? Or is there a way?

cisco_himg Mon, 11/23/2009 - 09:22

I forgot to give a little more detail...

I have 6 closets, in which 4 are running portchannel, and 2 are just regular trunk links.

THe 4 that are port channel are two fiber channels each coming from a Gig switch going to their respected closet. So each of the 4 closets have two fiber cables going there.

The 2 trunks are just one single fiber cable going to their respected closet.

Ok, so how can i tell the throughput on the port channels compared to the regular trunk links.?

glen.grant Mon, 11/23/2009 - 09:44

  Your port channel speed will be whatever the interface speed is that connects the 2 boxes .  It is not an aggregate .  If you have say a fastethernet port channel then your link speed will only be 100 megabits per second .  A ether channel gives you more pipes for your data but does not increase your transfer speeds .  A given conversation will only traverse a single link in that bundle so your speed is 100 meg.

cisco_himg Mon, 11/23/2009 - 09:46

Ok cool. they all come back to the backbone on a Gig switch. so i guess since there are two channels, it will be 2 Gig connections coming back to me, correct?

Correct Answer
Jon Marshall Mon, 11/23/2009 - 10:42

cisco_himg wrote:

Ok cool. they all come back to the backbone on a Gig switch. so i guess since there are two channels, it will be 2 Gig connections coming back to me, correct?

If there are 2 physical links in each channel and the physical links are 1Gbps each then yes your portchannel is 2Gbps.

Jon

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