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Redundant link for my Single Network

I have a single network across two geographic locations, the two locations are linked together by 100mb Ethernet link leased line through ISP-A. Both geographic locations are on VLAN2, VLAN3 [location A] and VLAN2, VLAN3 [location B], VLAN2 connects the two locations and Vlan3 is only used for management connection

I want ISP-B MPLS WAN link to backup ISP-A in case their Ethernet link went down. ISP-B is running HSRP across and MPLS network, with the active router on one side of the network and the standby on the other side. HSRP addressing are: Real IP -, HSRP IP - and Real IP -, HSRP IP -

I need to configure this network so that the LAN is not broken up when I ISP-A network went down and ISP-B will take over the connectivity of the LAN

Thanks in advance


Re: Redundant link for my Single Network

Is your ISP-B service MPLS IP VPN or is it MPLS L2VPN? From your description it sounds like it's L2VPN, but ask your ISP for clarification.

If it's MPLS IP VPN, then you'll need to cooperate with ISP to setup dynamic routing. Not difficult, we provide such things to customers on standard basis, so your ISP is likely to cooperate here.

If it's L2VPN, then it's only up to you to configure let's say OSPF on your routers and be there.

Should you need more details on solution, please post a network diagram including key elements of the network and let me know whether ISP-B has L2VPN or IP VPN.

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Re: Redundant link for my Single Network

ISP-B service MPLS is an IP VPN, I will appreciate a more detailed solution to try in my test lab before deployment. Attached is the network diagram. The important thing is connect within same vlan over two geographic location when the 100 link goes down.


Re: Redundant link for my Single Network


after looking at your diagram I've realised that the problem is a bit more tricky than I initially thought. You have layer-2 network (ethernet) interconnected by IP cloud and you want to run layer-2 over IP, i.e. somehow bridge over IP. Unfortunatelly GRE will not solve the problem because bridging is not supported on tunnel interfaces.

A colleague of me hinted that answer should be somewhere in the ancient SNA world of translated source-route bridging, DLSW and/or remote-source route bridging. We gave the idea quick try in the lab, but didn't succeed so far. Now I have a bit more time and going to give it another try.

If you're interested to evaluate this in parallel, here are couple links for reading:

and more generally:

I'll post an update either today or tomorrow.

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Re: Redundant link for my Single Network

Did appreciate your efforts

Re: Redundant link for my Single Network

I'm afraid I don't have good answer for you. Although I could generally get traffic passing across IP cloud, your setup calls for need to exchange IP packets between two routers across that virtual link (to have HSRP as you intended), not only systems behind them and that apparently unsupported functionality.

It seems the only way for you to utilise both Ethernet and MPLS IP VPN interconnections is to renumber two sites so each of them is in separated IP subnet. From your diagram looks like splitting /24 network into /25 is possible. After that you'll need to move your ethernet interconnection from switches to the routers (the same, which are connected to MPLS provider).

Sorry for keeping your hopes.

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Re: Redundant link for my Single Network

I hope some guru out there can still help, the customer has agreed to split the network, instead of having same network over two geographic locations we can have different network on each location and the two networks depend on ISP-B 4mb backup link. Thanks

Re: Redundant link for my Single Network

(Just got back from holliday)

If you split network into different IP subnets, then task is pretty straight forward: ask your MPLS provider which routing protocols they support (BGP is likely to be supported, OSPF may or may be not) and run the same protocol between your internal routers at each site and between your routers and MPLS provider. If you will run OSPF, then you'll need to configure sham-link between two your routers connected to MPLS provider. Let me know if you need more details on this.

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