Hi,
I have the following scenario which i need help with. We have internet connection provided to by 3 different ISP's. BGP is configured on the WAN facing interfaces of the switch. All the 3 WAN links are up and traffic is segmented through these based on certain policies. However for simplicity, lets consider all the traffic is sent through ISP1 (the primary link) only. Though the secondary ISP2 & Tertiary ISP3 links are up, no traffic flows through them for now. I would like to achieve the following:
1) If ISP1 goes down, failover to ISP2 link (provided the internet connectivity through it is UP).
2) If ISP2 is DOWN too, failover to ISP3 (again only if its UP).
3) If all the links are DOWN, dont do anything.
4) Lets assume ISP1 failure led to a switchover to ISP2 link. At anytime later, if ISP1 is back UP, i would want to dynamically switch back to ISP1 again.
5) Similarly if ISP3 is the current active link & if either ISP1 or ISP2 is back up, fallback to them.
Basically the cost associated with ISP3 > ISP2 > ISP1 & hence the above requirement.
I did read that IPSLA along with EEM can be configured to achieve such fail overs. I do see examples on the internet which explain fail-over when 2 links are involved, but couldnt figure out if other requirements in my question can be met using that. Can you please guide me with a sample IPSLA/EEM configuration if/how this can be achieved?
We have a Cisco Catalyst 4500X with the following firmware image:
Switch#show ver
Cisco IOS Software, IOS-XE Software, Catalyst 4500 L3 Switch Software (cat4500e-UNIVERSAL-M), Version 03.08.06.E RELEASE SOFTWARE (fc4)
Compiled Thu 05-Apr-18 08:05 by prod_rel_team
Thanks in advance.
