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internet failover options

i have 2 sites with one internet connection and we are adding one more circuit for redundancy, ideally we want the failover to be dynamic and fail back when the primary circuit comes up.

can this be achieved with a router? which model? is it better to use a firewall instead?

how does the failover and fail back work? ip-sla or routing?

Marwan ALshawi

Sure you can

See the below document

Hope this help

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Hi Ronni,

You can achive this with BGP multihome which can be done between two provider links.
We have this same kind of setup at one of our Data Center and it is working well with 0% down time.

You can do this setup with routers like 1841, 2951 and so on it depends on the traffic that the rotuers going to handle.

Of course the IP SLA can work for this but BGP multihome will be more effecient than this.

Please rate the helpfull posts.


Bgp is not 0 downtime because it will take seconds or couple of minutes till bgp timers end or bring down the bgp session for failover

On the other hand bgp multihoming is not always the case when then provider might use static route or rip for example

In other words each situation is different and bgp is only one possible option

Hope this help


Hi Ronni,

The answer will depend upon what you are using those Internet links for, and a little more information about your topology is required...

  1. You mention that you have 2 sites, with 1 Internet connection.  Do you mean that there is one internet connection at EACH site?
  2. How are the sites linked together (if at all)?  Does one site have an internet connection and the other site is linked directly?
  3. Where will this second Internet connection go?  Or will this be a second internet connection into both sites?
  4. Can you provide a simple diagram?

If you are using the connections just for users to connect out to the internet for browsing etc and you use Private (RFC1918) addressing internally, You can simply have multiple default-routes out of your network, advertised in using whichever routing protocol you use (OSPF, EIGRP, RIP etc)

Outbound traffic can be sent either to the 'nearest' gateway or to a predefined Primary with secondary failover.

Traffic will be NATed as is goes through your gateways to the Internet IP addresses for that link, meaning that return traffic will come back the same way.

This is just one option of MANY, and makes some assumptions which may not be correct.

Please provide some additional info, and someone will be able to provide a better response.



The ip sla with pbr will work, thank you.

By the way, in terms of chosing the correct router, we have about 50-75 people in the site do you think that a C1800 can handle the load? 800 will be low end right?  which router will be handle the load?

Hi marwanshawi,

I would say with BGP multihome it is 0% outage because I have it at one of my site and also when we did BGP failover test without single packet drop (RO).

Ronni, I would suggest you to go with with C1800 router because the 800 is very low end series and also you should consider that feature expanses also.

As I said in my previous post, Yes IP SLA will also work for you.

Please rate the helpfull posts.

When you did the test did shut down the bgp peer or the interface ? If yes this will be quick but if the link is up but the other end bgp is not up then bgp timers will use the hold time timer which is by default about 3 minutes

Ronni make sure you rate the helpful posts


I did the test by unplug the WAN interface and put continue ping to internet gateway no RO
Even when plugged back no RO.

Do you know that all was done without notify that the link down or packet drop.

Please rate the helpfull posts.