We currently have 3 sites (A, B, C) interconnected by a Layer 3 OSPF triangle: A <-100Mb/s-> B <-1Gb/s-> C <-40Mb/s-> A
All WAN links are in fact Layer 2 WAN links.
I'd like to simplify this architecture by eliminating the OSPF Layer 3 on the Layer 2 WAN links.
Site A should communicate with the 2 other sites. I'd like that sites B & C should be seen as one site.
This should be possible if we create a kind of 'Etherchannel' between Site A and site BC where we would regroup the physical links A <-> B and A <-> C in a logical link A<->BC.
WAN links are currently interconnected on Layer 3 switches (3750G or X series)
I'm not sure this is possible with this kind of switches? I have thought using the Nexus family (5K series with 2K FEXs) but there the issue to create a VPC are the L2 links (A <-> B and A <-> C are 100Mb/s and 40Mb/s connections) which are below the 1Gb/s interfaces of the Nexus switches.
If anyone should have a solution to create this 'etherchannel' like link, I'm interested. Especially if we could use the 3750 series?
Thanks for all who are reading this question
I would keep the current setup because playing with OSPF metric you can take in account the different speeds of the links.
How an etherchannel like technology could handle two member links with different effective speeds? A-B link is 100 Mbps and A-C link is 40 Mbps.
You could be able to use an etherchannel bundle but it is not recommended at all until the real speeds are so different.
You could easily end with the 40 Mbps link congested.
If you can upgrade the AC 40 Mbps to 100 Mbps you could consider the move.
However, you could still join the B and C site over the 1Gbps link making it a L2 trunk, but that would be a single point of failure in your network if the B-C link fails you would end up with splitted IP subnets and dual active HSRP on client vlans and so on.
An additional link between B and C site is recommended before joining the sites.
Hope to help
I agree with Giuseppe. You should keep it as later-3. Also, one of the restriction for configuring an Etherchannel is to have the same speed and duplex for all physical interfaces. So, you can't build an Etherchannel with one link being 40Mb and the other one 100Mb or one link 100 and the other 1000.
Thank you for your answers and the helpfull link.
Now if I consider to upgrade the 2nd link to 100Mb/s should this be possible? If yes how? with the 3750, with Nexus or with some other appliances?
once the links A-B and A-C are of equal speed at 100 Mbps you can build the etherchannel using C3750 you don't need a Nexus for this. The issue is on the different current speeds that cannot be taken in account by etherchannel technology.
Hope to help
The link B <-> C is a L2 WAN link (about 30 km); This mean there's no stack cable between the 3750 switches. Is it still possible to create an etherchannel from A to BC (see details in my 1st post hereabove)? If yes, can you tell me with which commands?
I was missing this key point the distance between siteB and site C.
You are right you cannot build a stack of C3750 over fiber, as a result of this you cannot build an etherchannel as the two C3750 in B site and C site are two different devices from the point of view of site A
I'm afraid it is better to keep the current setup with OSI L3 indipendent links and OSPF.
Hope to help
I know that with the Nexus switches it's possible to achieve this 'distributed' etherchannel on 2 different switchs. This is possible by using VPCs. The issue I have with these VPCs is that the Nexus switchs have as minimum bandwidth 1Gb/s ports...
I would like to find a device with the 'VPC' functionnality (or similar), but with lower speeds as I have in my today's WAN architecture.
you could use a VSS with two C6500 with appropriate supervisors you would need multiple 10GE links between site B and site C. Then on the C6500 pair you could have a C6748 linecard in each chassis and a port running at 100 Mbps and the two ports configured as a etherchannel from the VSS to site A.
However, using a 2 x 6500 VSS when your WAN links are 100 Mbps look like too expensive, isn't it ?
And you would need 2 x 10GE links between siteB and site C to build a reliable fault tolerant VSS
Hope to help
Thanks for your help trying to find a solution to my issue. Unfortunately we can't afford such a huge investment
I think we'll have to remain with our Layer 3 OSPF triangle.
I still doubt about a solution with the Nexus, but I can't see how.