Posted on August 14, 2019 3:22 pm
 |  Asked by Warren Granada
 |  197 views
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Good day

I have a Arista DCS-7148S-R running V4.9.7 yeah I know old but that is what I have to deal with, anyways
this switch is in London and has a default route pointing all traffic to use the internet here in Chicago.
I am currently in the process of ordering internet in London and I would like to set all traffic that
doesn’t have a route to use the new internet connection out of London and use the Chicago internet as back
up. How do I go about setting this up?

Thank you in advance!!

Warren

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Posted by Tyler Conrad
Answered on August 14, 2019 4:12 pm

If I’m understanding the question correctly, you want to have specific paths advertised via Chicago, with a default route via London, but also want the capability to fall-back to Chicago for the default route in the event that London ISP goes down?

That should work fine, you just need a mechanism for withdrawing the default route from London if the path is determined faulty. What device will be connecting to the ISP directly? Can it form a BGP/OSPF peering with your 7148? If that box can withdraw the default route itself if the path has a fault, what I would do is:
– Send default route + specifics from Chicago.
– Send default route from London, with higher local-preference on import.

Hope this helps,
-T

What I want to do is use the London ISP for the local boxes in London to go out the internet in London and if the ISP in London goes down I want the traffic to go over to Chicago and out the internet in Chicago. I will be using a ASA 5516 to connect directly to the ISP I was thinking on the switch do something like

0.0.0.0/0 10.16.184.154 250 – Chicago
0.0.0.0/0 10.16.10.5 100 – London

I am thinking that would work…your thoughts??

(Warren Granada at August 14, 2019 4:53 pm)
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Posted by Alexis Dacquay
Answered on August 20, 2019 3:23 pm

Hi

Warren,

You can failover automatically if the physical link to your ISP goes down. If you also want to support indirect failures, then you can run a script to check remote services (ICMP or DNS) and take actions upon it: either install or withdraw static routes.
Here are two articles building this solution:

https://eos.arista.com/reachability-health-checks/
https://eos.arista.com/ip-static-route-with-health-check/

If for some reasons the above solution does not work for you, for example if your EOS being too old, then you can use the below method with a bash script.

https://eos.arista.com/forum/ip-sla-rechability-route-tracking/

Best regards,
Alexis

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Posted by Tony Li
Answered on August 20, 2019 3:35 pm

Another common approach is to have your London ISP advertise you default via BGP.

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