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I'd like to have my Cisco router failover from a primary WAN to a secondary WAN interface when the primary stops routing traffic. Neither WAN is running any routing protocol, these are residential-type WAN connections (ie, DHCP).

I don't have any need for maintaining source addresses. In either case the traffic would be NAT'd out whatever the appropriate WAN is.

How do I configure this setup in iOS?

If it matters, I have a Cisco 890-series branch router. Thanks in advance.

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  • OK, then do what you described. What is your question?
    – Ron Maupin ♦
    Aug 14, 2016 at 21:55
  • Question is How do I configure this in iOS. I'll clarify the questions.
    – Pablo
    Aug 14, 2016 at 22:02
  • Unfortunately, questions about home networking are explicitly off-topic here. You can try to ask this question on Super User.
    – Ron Maupin ♦
    Aug 15, 2016 at 14:26
  • Maybe but this is how I learn about networking. I use professional equipment and real world scenarios. The underlying media is less relevant. If I were doing on behalf of one of my small business clients, who increasingly need internet redundancy this would also be a valid inquiry.
    – Pablo
    Aug 15, 2016 at 14:29
  • @RonMaupin Not many home networks have their own ASNs / IPv6 allocations. This is not a typical scenario the policy refers to.
    – Pablo
    Aug 15, 2016 at 14:30

2 Answers 2

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if your IOS has IPSLA you should be able to:

  • create a ping object for each router (ping something out on the WAN)
  • use HSRP on the LAN interfaces
  • devices use HSRP address as default gateway
  • track the ping object to alter HSRP priority appropriately
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  • How can I tell if my router has IPSLA?
    – Pablo
    Aug 15, 2016 at 11:54
  • conf t then ip sla ? I think
    – marctxk
    Aug 15, 2016 at 12:47
  • IP SLA works if you can have the address of an upstream device to track, but it doesn't seem to help with DHCP on a single router. Also, HSRP on the LAN is useless unless you have two routers, which doesn't seem to be the case here.
    – Ron Maupin ♦
    Aug 15, 2016 at 14:06
  • Can IP SLA be used to add/withdraw routes? I think IP SLA plus the AD that @RonMaupin described would be a workable combination. 1) Suppress the DHCP default route. 2) ip route 0.0.0.0 0.0.0.0 eth 0 dhcp 100; ip route 0.0.0.0 0.0.0.0 eth 1 dhcp 50; 3) then use IP SLA to change the AD 100 route to an AD 25 route based on reachability (anything would work e.g. 8.8.8.8)
    – Pablo
    Aug 15, 2016 at 14:09
  • @Pablo, the AD of the DHCP default route is so high that any route you configure with a lower AD will take precedence, and the DHCP default route will be suppressed. IP SLA is useful to track your upstream router, but you will need to know its address when you configure IP SLA, and you can't know that with DHCP. Since this is for a business, you should really get a static route, at least on the primary WAN circuit.
    – Ron Maupin ♦
    Aug 15, 2016 at 14:14
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The easiest way is probably to use AD to create floating static routes. I assume you are using a default static route. Use one for each WAN connection, and specifically set the AD on each. The lower AD is preferred. When the preferred port is down, the route will be withdrawn from the routing table, and the route with the next lowest AD will be preferred.

Something like this:

ip route 0.0.0.0 0.0.0.0 <Interface 1> <PE address 1> 5
ip route 0.0.0.0 0.0.0.0 <Interface 2> <PE address 2> 10
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  • Can you clarify what AD is? And what if the link isn't down but just unreachable (consider a failed router upstream)
    – Pablo
    Aug 14, 2016 at 22:15
  • AD is administrative distance. It tells the router how trustworthy the route is compared to other routes which are the same. If you get the same route using RIP, EIGRP, OSPF, iBGP, and eBGP, the route from eBGP will be preferred because the AD is 20, but if it goes down, then the route from EIGRP will be preferred since the AD is 90. If your upstream router fails, then the link should fail. You can include the upstream router's address, too.
    – Ron Maupin ♦
    Aug 14, 2016 at 22:22
  • How would I assign AD on DHCP generated default routes?
    – Pablo
    Aug 14, 2016 at 22:32
  • Don't accept default routes from the interface.
    – Ron Maupin ♦
    Aug 14, 2016 at 22:38
  • Looking at a Cisco router that gets a default route from the carrier because of DHCP, the default route has an AD of 254, which is the highest it can be without being unreachable. Any you assign with a lower AD will take precedence.
    – Ron Maupin ♦
    Aug 14, 2016 at 22:44

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