Does LACP or PAGP Aggregate bandwidth

[dbuckley77]

Can someone please tell me if I had an LACP or PAGP etherchannel between two gig ports on one switch and two gig ports on another switch if I would get 2gig max throughput.

[Reza Sharifi]

No, your maximum throughput is still 1Gig, but you have more links to use.  So, one host can send one packet using one link and the next host can send a packet using the other links. Think of a highway with one lane vs one with 2 lanes.  You got more lanes to use but you can only go as fast as the speed limit.

HTH

[dbuckley77]

So we're currently seeing traffic on a gig link routinely hitting 800mbps.  Would a creating an etherchannel with LACP/PAGP be a good way to alleviate some of this or would there be some way of creating a lag by combining with another 1gb port at each end of link?

[Reza Sharifi]

Yes, that would help, because some of your traffic will use one of the one Gig link and some the other one.  It is not 50/50 but you should see good improvement.

HTH

[Joseph W. Doherty]

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Posting

Just to re-emphasis, Etherchannel directs flows to a single link.  So, no one flow will be able to obtain more than one link's bandwidth.

Etherchannel distributes flows across the links based on "hashing" some L2 or L3 attributes.  Poor algorithm "fit", will often result in poor distribution of flows across links.

Generally, distribution works best with a power of 2 number of links.

Etherchannel doesn't track link usage, so flows will be directed to links regardless of their current usage.  On average (with good hash), two links effectively provides about a 50% bandwidth increase for multiple flows.  (Consider, for example, 1st flow will be directed to a link, 2nd flow, if two links, has a 50/50 chance of being directed to the already used link, or to the unused link.)

[Carlos Villagran · Accepted solution]

Hi!

It does, it increments your available bandwidth, HOWEVER this applies only to L2 Etherchannels. 

Also, take in mind load-balancing methods since if not implemented correctly the traffic will not be balanced equally or one of the links will get way more loaded. 

Here is a document explaining the balancing algorithms in case you are willing to dig further on it:

http://www.cisco.com/c/en/us/support/docs/lan-switching/etherchannel/12023-4.html

Let me know if you have any other question!

Hope it helps, best regards!

JC