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How to utilise two Ethernet WAN links for combined bandwidth?

Hi all,

I would like to ask for your kind help on the following scenario.

A customer of ours currently operates a main office in London and is going to open a branch office nearby.

For the interconnection, they chose a resilient 1Gbps metro ethernet link (two ethernet connections, 1Gbps full duplex each, copper interface).


<=> : Resilient metro ethernet link (2x1Gbps).

Apart from resiliency, I am investigating the option of combining the two links for 2Gbps of total aggregated bandwidth (when both links are working). In case of a failure on one of the links, of course total bandwidth will be reduced to 1Gbps full duplex.

Any ideas how to do this with routers (preferably 2900 series)?

I am currently working on the WAN architecture so any option can be considered. I already thought of going for L2/3 switches and LACP/PAGP, but I am not sure if the metro ethernet supplied by BT's openreach can support this. Any ideas?

Thanks for your help!





You're probably best establishing what type of connectivity BT are a actually delivering what's the exact product type you ordered?

For example BT EAD (Ethernet Access Direct) will carry LACP/PaGP.

However if it's an MPLS derived service i.e. EVPN or E-LAN then chances are LACP/PaGP control packets won't pass...

Cable & Wireless in the UK certainly don't pass LACP over MPLS EVC's.


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Hi Dunc,

thanks for your answer.

The service ordered is Openreach EAD.

So what do you think? L2/3 switches?

Thanks again,



You can do both really, as far as I'm aware (will be worth a check) "most" routers support LACP/EtherChannel as well so you've got potentially both options available.

Ultimately it depends what you want run over the links and what extra services you need to provide, for example if you want really flexible QoS / Shaping etc you'll be better off with routers.

Perhaps a little more background?


Hi again,

the links will be used for Citrix XenApp for 75 users, VoIP and storage replication (during business hours), as well as backup (off-peak hours). Traffic engineering will be needed. This business belongs to an industry that uses CAD-like software that generates huge amounts of data: some users in the branch office will be working on project files large as 300-700GB. These files will have to be backed up to the central office during the night.

I was thinking of 2911/2921 routers, two of the onboard GE interfaces with etherchannel facing the LAN, the third onboard GE and a EHWIC-1GE-SFP-CU facing the resilient link. Then I noticed the throughput of 2900 series routers; it's 180-250Mbps. I am impressed, I cannot understand how anyone can use the three onboard gigabit interfaces if the router has that level of performance?

Please tell me what you think.

Thanks again,


Correction, it seems that the document I was referring to previously was totally inaccurate. According to the "Cisco Integrated Services Routers - Performance Overview Whitepaper" 2921 router throughput is 3,5gbps for 1500-byte packets.


I would urge that you check other sources to clarify the throughput limits of each router, I've always used the following link as a rough basis for equipment sizing.

And the 3.5Gbps is assuming 1500 byte packets, you'll find a decent mix of packet sizes on the wire in a real envrionment, for example Citrix & ICA will use a lot of background control traffic that won't be 1500-byte packets.

Let me know your thoughts.


Hi Dunc,

This was the document I was reading. Indeed, with NAT, QoS, ACLs and IMIX Traffic at 75-Percent CPU, performance goes down to 105Mbps for a 2921 router. I do not plan to run NAT or ACLs, but QoS will have to be implemented. I haven't found a document describing QoS performance on ISR G2s with QoS but I suppose it will be much lower than the figures I'd like to hear.

So... would you go for another solution to avoid wasting money on 1 gig links without the appropriate routing platform behind it to support the bandwidth? For example, 3750-X switches?

Thanks for your help.


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