Bandwidth

Unanswered Question
Feb 26th, 2009

Scenario: I have a 3560 switch. 48- 100Mb ports and 4 - 1Gb ports.

Can the 4 - 1 Gb ports combined really handle 4 Gbps of total throughput or provide 4-Gbs of bandwidth?

How about the 100 Mb ports? 48X100 = 4.8 Gbps, is this really possible?

What are the real world numbers and expectations for devices based on their port ratings?

I have this problem too.
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adamclarkuk_2 Thu, 02/26/2009 - 13:51

I believe you are talking about etherchannel (802.3ad).

You can only bundle 8 ports together at once (not 48, that would be cool).

You do this using the channel-group as an interface level command :-

switch(config)#interface range gigabitethernet 0/1 - 4

switch(config-if-range)#channel-group 1 mode on

In this example I have selected 4 interfaces and put them into channel-group1 which will create a Port-channel interface where all future config is applied. I will now have a 4 gig Port-channel that will share the load using an algorithm (which is configurable on on per device level) see the link below :-

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml')">http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

Etherchannels can be layer 2 or layer 3 and not only 'increase' bandwidth they also provide redundancy.

Sam Smiley Fri, 03/13/2009 - 12:23

What Adam said is correct about Ethercahennel, however don't be confused about the bandwidth. With Etherchannel it doesn't work like you have a single 4 Gb link. While it is true that you have a total of 4 Gb you actually have 4 1 Gb links. Basically if you try to transfer something through the EtherChannel from a single host you will see a mazimum transfer rate of 1 Gb, not 4Gb. Etherchannel does provide redundancey and increased available bandwidth.

Regards,

Sam

Chad Peterson Fri, 03/13/2009 - 18:31

When we send packets out an etherchannel on a switch, we do not load balance on a per packet basis. We will run a hash to determine which link that packet will go out of.

You can check the algorithm used by running:

'show etherchannel load-balance'

If you find that 1 link gets utilized more than others you can change this via:

'port-channel load-balance ?'

You can then configure a different method to load-balance.

And to your first question...8 ports max in a channel group.

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