Etherchannels

Unanswered Question
Jul 7th, 2007

How do I bias an etherchannel?

I have one group of etherchannels(2links).

1st link = 100Mbit/s

2nd link = 20Mbit/s

How do I make all the traffic go over the faster first link and then only over the 2nd link if the 1st link fails?

Is it possible to make UDP traffic go over the same link all the time ?

Thanks in advance

I have this problem too.
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Anand Narayana Sun, 07/08/2007 - 00:31

it is not possbile to make etherchannels if 2 links are having different speed, it won't even form a etherchannel when you like this. only the following combinations are possible.

1st link - 100Mbps

2nd link - 100Mbps

1st link - 1000Mbps

2nd link - 1000Mbps

like this maximum u can form 8 ports to act as 1 virtual link of 800Mbps or 8Gbps.

wazzaclarke Sun, 07/08/2007 - 01:10

I have created the etherchannels and they work perfectly. Traffic goes over both links simultaneously and if one link fails then all the traffic goes over the link that is still up.

Is there a better way of doing this with 2 links that are different speeds? The etherchannel exists between a Layer 3 3750 and a layer 2 2950 switches, the etherchannel act as a layer 2 channel.

Is it possible to use the layer 3 as a router to do this, if yes please explain how I would do the above.(this post and my 1st post)

Thanks

Anand Narayana Sun, 07/08/2007 - 01:29

As i mentioned in my previous, configuring etherchannels is possible only with the same speeds & not with different speeds.

also etherchennel is possible on the router also provided the watt ethernet module you use. but if say that u wanted to combine 2 serial link with the remote end router, then YES it is possible by configuring Virtual templete interface.

Note

wazzaclarke Sun, 07/08/2007 - 01:59

you are not listening. I have configured the etherchannels with the different link speeds and it works. No PROBLEMS.

I need to know how to send the majority of the traffic over the faster link?

If you think this is a bad way of doing combining two links, then give me a better way so that I can use both links to send data and if one fails, all the traffic will go over the remaining link.

cristiangal Sun, 07/08/2007 - 03:22

you cannot get 20Mbps link speed on a fast ethernet port, the capacity of that layer2 circuit can be 20Mbps but the physical port is fast ethernet and thats why your etherchannel works. unfortunately you cannot tell to a cisco that one port is only 20Mbps capacity so it will balance equally on both ports.

wazzaclarke Sun, 07/08/2007 - 10:05

Can you suggest a better way then please ?

my primary link is a laser(100Mbit/s)

backup link wireless radio link (20Mbit/s)

Layer3(3750)------------Laser--------Layer2(2950)

------------Radio--------

What is the best way of making these link redundant then?

Edison Ortiz Sun, 07/08/2007 - 07:00

Warren,

Can you tell us how many ports were used for the first etherchannel to achieve the 100Mbps link ?

Can you tell us about the second link as to how many ports were used ?

Are both bundles connecting from the same source device (switch) to the same destination device (switch) ?

Can you post the output from typing

"show ether sum" from the 3750 switch as well as "show spanning-tree".

And addressing your other queries:

"Is it possible to use the layer 3 as a router to do this, if yes please explain how I would do the above."

Well, you can do L3 etherchanneling when both switches are L3 capable. 2950 is not, therefore it won't work for your environment.

In your environment, the traffic manipulation can only be done with STP since it pure L2 etherchanneling.

Thanks.

wochanda Sun, 07/08/2007 - 09:27

Etherchannel is implemented in hardware, and uses a hash based on source/destination MAC and/or IP and port # to decide what link each packet will take. It will only work on equally capable and configured links, such as 100mbit or 1000mbit. There is no configurable or built-in intelligence about policing downstream, so you cannot weight one link over another.

To achieve something very similar, though, you can rely on the load-balancing built into some of the more advanced routing protocols, such as EIGRP. In this case, you would configure each port as an independent L3 link on each side, letting adjacencies come up on both links. You then use the 'bandwidth' under each interface to let the switch calculate costs differently over each link. You then manipulate the 'variance' command under your EIGRP process to allow you to load-balance over both links.

More about all this here:

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a008045296f.html

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml

This will work on all routers and L3 switches such as the 3750.

Mabry Tyson Thu, 04/07/2011 - 01:45

I'm sure the original poster has long since resolved his issue.  But if anyone else gets here (as I did) looking for a solution as to how to failover from one link to another, check into Flex Links on newer switches:

"With Flex Links configured, one link acts as the  primary interface and forwards traffic, while the other interface is in  standby mode, ready to begin forwarding traffic if the primary link  shuts down."

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