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I have a Cisco router with two ISPs connected to it, and I wanted to configure a failover between them using an IP SLA, track for the IP SLA and two static routes (when the first route fails, the second becomes the primary). However, it turned out that the IOS on the router does not support IP SLAs, because it does not have the appropriate license (which costs $1000, and buying it is not an option). I tried to use the predecessor to IP SLA, the "rtr" command, but it's not supported either.

In this case, is there something else I can use to achieve failover functionality?

Thank you in advance.

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  • What version are you running? Is OER or PfR available?
    – Ron Trunk
    Mar 1 '17 at 12:27
  • The version is 15.4, and both "oer" and "pfr" commands are not available (when I try to set a master controller).
    – peter_s
    Mar 2 '17 at 12:27
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The simplest way to achieve a failover is by using floating static routes. You are going to need a default route (0.0.0.0/0) to your ISPs. Cisco has AD (Administrative Distance) that basically tells you which of identical routes is preferred. Static routes normally have an AD of 1 (lower is better, like golf), but you can give a static route a specific AD. When an interface goes down, the route is withdrawn from the routing table, and an identical route with a higher AD will then take over.

For example (where 172.1.2.3 is ISP 1 and 10.11.12.13 is ISP 2):

ip route 0.0.0.0 0.0.0.0 172.1.2.3
ip route 0.0.0.0 0.0.0.0 10.11.12.13 10

Both commands create an identical static, default route, but the first command leaves the AD as 1 to the primary ISP, while the second command sets the AD to 10 to the secondary ISP. If the interface to the primary ISP fails, then the default route automatically fails over to the secondary ISP.

This works if the interface on the router loses connection to the ISP (Down/Down or Up/Down). It may be possible, depending on the physical connection to the ISP, that your interface still shows Up/Up, but for some reason the ISP doesn't respond, and this this configuration will not work correctly. That is where IP SLA would work.

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