We have recently signed up for Metro Ethernet for our main campus and 8 branches. It's a "mesh" with the carrier providing a virtual layer-2 switch in the cloud. I have a Cisco router at each site running EIGRP and they all have neighbor relationships with one another on their "WAN-facing" interface.

The carrier has provided a second circuit into the main campus, which comes into a different building via a completely diverse path. That's good because there's a lot of construction going on at the main campus. I'm trying to think of the best way to provide failover. Load balancing isn't necessary since each branch has 100 Mbps and the main campus has 1 Gbps, so even without load balancing, there's no way that the 1 Gbps could be saturated. That connection is currently terminating in an ASR1001-X at the main campus.

Each campus also has a backup Internet connection running between 7 and 60 Mbps terminating via DMVPN into an ISR-4431. I mention that because I'm fine if terminating the second Ethernet WAN connection is done in the same ASR1001-X as the “primary” line if that makes it easier.

Here are some possibilities...

  • Both connections into the ASR
    • Have a normal interface and a backup interface. However, since the WAN connections terminate into a CPE, the link light probably wouldn't go off even if the back-end connection is experiencing trouble. I saw an article on Ethernet CFM but haven't really looked into it yet.
    • See if the carrier supports VLAN-trunk interfaces. That way I could have two virtual connections at each branch and let EIGRP manage what's up and down based on keepalives/neighbor relationships. This would also provide load balancing (which I don't really need). I'd rather not screw around with dot1q sub-interfaces or worry about tagging to the carrier, but if need be...
  • Terminate the second connection into a different router (e.g., the aforementioned 4431) and adjust stuff like bandwidth and delay so EIGRP doesn't mark it as equal-cost.

Anybody had this scenario and found an ideal solution?

1 Answer 1


I don't see why you can't have two interfaces and just let the routing protocol decide which link works, and which doesn't. You could manipulate the delay on one if you want an active/standby setup, but that doesn't require two routers, or you could do it with two routers. That is the real point of dynamic routing protocols.

If it takes too long to fail over for some things, so you could run BFD.

  • You can't have two interfaces on the same subnet on the same router.
    – theglossy1
    Commented Apr 19, 2017 at 18:10
  • If you have two different circuits, they are normally using different networks. Having two interfaces on the same link isn't really a backup. If the fiber is cut down the street, you lose both interfaces. We have discovered that it is far more likely that you lose a link due to external problems, than if you have a hardware failure. We have several levels of redundancy. Multiple circuits (preferably on different carriers, but to different PoPs if the same carrier) is the primary level of redundancy. Using the same carrier and circuit really provides nothing extra.
    – Ron Maupin
    Commented Apr 19, 2017 at 18:14
  • They threw it in as part of the package. It's a diverse route (physically). We already have external redundancy over DMVPN with a different carrier. This is a management decision that I was set up with. We settled on the Q-in-Q approach anyway, so I withdraw the question your honor. I'll mark yours as the answer because BFD is something I hadn't thought of and is intriguing.
    – theglossy1
    Commented Apr 19, 2017 at 18:27
  • You should edit your question to better describe the network. A diagram would go a long way. You are revealing details in your comments that are not clear in the original question. If you want a good answer, then you should include all the relevant details in the question.
    – Ron Maupin
    Commented Apr 19, 2017 at 18:29
  • I did mention those things in my original question (DMVPN, diverse paths). I haven't wanted to invest more time into my question by providing diagrams, etc. Anyway, we can let it be... no more comments necessary.
    – theglossy1
    Commented Apr 19, 2017 at 18:31

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