Etherchannel over WAN links

[sumedhgujar]

Hi, 

We are having Cisco 1941 router each at our 2 locations, Currently we are having only 1 wan link between these 2 locations. We are planning to take 1 more wan link from other ISP for redundancy and for load balancing. 

I am little bit confused whether etherchannel will work or not over WAN links from 2 different ISPs or do we have any other option to achieve our goal ??

Thanks in Advance

Sumedh

[Mitchell.Drage]

Hi Sumedh,

It's very unlikely that an etherchannel will work, as any standard etherchannel establishment protocol has a unique ID that defines who you are as a device, and if your one device connects to two WAN routers, those two routers are likely not seen as one device from an LACP or PAgP perspective so both links will be seen as Independent ports, rather than aggregated in-bundle. That's not to mention the issues that you will have with unidirectional connectivity at Layer 2, causing all layers above to fail.

An 'on' mode etherchannel can circumvent that ID issue, but will not be worth investigating for most situations. I'm only adding this for completeness, not because it is a viable option.

I would say that it is safe to assume that you cannot run an etherchannel to your WAN provider, and I recommend looking at what routing protocols they with allow you to use. e.g. you can use BGP with most providers that I have come across, and you can advertise different networks out each link.

It requires some administration, but it works and is well-understood in the network community.

Hope that helps.

Regards,

Mitch

[sumedhgujar]

Hi Mitch,

Thanks for your explanation, 

Currently we are not using any dynamic routing protocol so only for one location we dont want to introduce routing protocol.

What if we will take L2 links from both ISP and we will connect both links on one router at both locations and then configure ether channel? But what if 1 link will go down in etherchannel as ethernate port doesnt get down then how traffic will shift to other. This is also 1 concern. 

Thanks in Advance

Sumedh

[Mitchell.Drage]

As far as I am aware, at Layer 2 level, the traffic won't shift over at all.

My understanding is that an etherchannel will establish, or attempt to establish a peering with the device that it is connected to (the WAN provider).

If you had a Layer 1 link (wavelength, dark fibre, maybe even a psudowire (not sure on that one)), you could use an etherchannel, but I don't think a Layer 2 link would work as there isn't any mechanism for sensing an intermediate failure. Your links would stay up and your switch/router would be using the etherchannel load balancing mechanism to select which link to use, and black-holing around 50% of your traffic.

[paul driver]

Hello

As stated  Etherchanneling doesnt  sound like a viable option in this case Do these two sites share the same network?  - The options you  could have I guess would depend on what routing process you have implemented (static or dynamic)

 If dynamic routing then path manipulation can be performed via route metrics and in case of a outage failover will be perform by that routing process

alternatively with static routing the same result can be  performed in conjunction with io sla tracking  

[Joseph W. Doherty · Accepted solution]

As the other posters have described, Etherchannel is a L2 technology used between a pair of devices, With two different providers, I don't see it as being possible.

Since you have a pair of Cisco router, why not just equal cost route across two L3 links? (Unsure the 1941 supports it as a feature, but if it supports PfR, you could dynamically load balance across your two links. Something not possible with Etherchannel,)