Does EtherChannel support load balance?

[Steve Zhou]

Hi all,

I did a two port EtherChannel from a dual-port server (two 1GbE) with a Cisco switch (1GbE ports) and I have the following questions:

1. Will the bandwidth between them become 2Gbps?

2. Are both links active, which means the traffic would be spread accross both link (load balance)

3. What is the MAX number of ports supported in a single EtherChannel?

thank you!

[cadet alain]

Hi,

1. you multiply the bandwidth of the links by the number of links

2.http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/54sg/configuration/guide/channel.html#wp1020414

3.   maximum of 8 bundled ports.

Regards.

Alain

Don't forget to rate helpful posts.

[Steve Zhou]

thank you, cadet alain.

I failed to understand the following statement from the link you provided:

”Because some linecards have a maximum bandwidth capacity toward the backplane, they can limit the aggregate bandwidth of an Etherchannel when all the Etherchannel members belong to the same linecard."

Does the backplane here refer to the linecard backplane, not the switch backplane? Sorry for such a silly question as I'm new to switching technology.

[Karsten Iwen]

Start with the following reading:

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml

1. Will the bandwidth between them become 20Gbps?

with two links of 1 Gig the theoretical maximum bandwidth will be 2 Gig. But that will typically not be achieved due to the load sharing algorithms.

2. Are both links active, which means the traffic would be spread accross both link (load balance)

Yes, all active links will be used if you have enough flows. But keep in mind that one conversation will only be on one link.

3. What is the MAX number of ports supported in a single EtherChannel?

Typically you can have eight active links.

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[Steve Zhou]

thank you, karsten.iwen. By the way, were the two NICs being teamed (NIC teaming) together in such a configuration? I'm thinking how does the server send traffic across both NICs? It shouldn't be controlled by the switch side. Does it mean NIC teaming controlls traffic sending in a load balance way?

Originally, I thought NIC teaming is a different thing from EtherChannel, but in my case, it seems that both NICs were teamed together.

How do you think?

[Karsten Iwen]

EtherChannel is a one-way thing. If you connect a server with two nics to a switch, the server is reponsible for splitting the traffic onto the two links. For that, sometimes an advanced nic-driver has to be installed on the server. This is also named nic-teaming, but it is available in many flavours. Some provide only fault-tolerance and some also load sharing. Look for the terms LACP or 802.1ad on the configuration-guide of your OS.

The same way, the switch is responsible for splitting the traffic that is send to the server. That's done in the local switch-config.


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[Andras Dosztal]

For the 1st question: think of it as a highway. The speed of a car (a single data stream) can't be more than the permitted maximum (1 Gbps), but if you have more lanes, more cars can pass by.


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[Steve Zhou]

Very interesting analogy. In my case, does it mean that I would have 2 lanes in this EtherChannel. So I would got 2Gbps bandwidth in total in theory?

[Andras Dosztal]

In theory yes, but you need at least two streams and they have to be hashed to a different member of the port channel.

[Steve Zhou]

I got it, 2Gbps is always there, but whether the entire 2Gbps could be fully utilized depends on the load balancing method.

Thank you, Andras!

[Karsten Iwen]

> but whether the entire 2Gbps could be fully utilized depends on the load balancing method.

and on the amount of flows that can be balanced over the link.


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