Internet redundancy with 3 different ISPs

[byme88]

Hi Team,

Can someone please help, any idea is truly appreciated! I have a scenario design as explain below:

I have a 4331 ISR router, which has 4 Gigabit interfaces. 3 of these are connected to 3 different ISPs for internet access..

I would like to configure the router for 3 ISP connection as redundancy only, no load-balancing.

Scenario:

ISP1 is Primary ----> always ON, and is PRIMARY

ISP2 is Secondary -----> if ISP1 goes down, then ISP2 will come in play

ISP3 is Last choice -----> if both ISP1 and ISP2 are down, then ISP3 will take over

And when either ISP1 or ISP2 come back, whichever come back up first, should take over.

If both ISP1 and ISP2 come back up the same time, ISP1 should be the Primary again.

I am thinking of using SLA Tracking, but open to any suggestion. Can some expert please help and shed some light?

Much appreciated!

Xy Le

[MHM Cisco World]

three ISP with IP SLA is not for my view good, 
instead use PBR with  
set ip next-hop verify-availability  
and the order of PBR sequence is depend on what ISP you want to be primary and backup1 and backup2.

[byme88]

MHM,

Thanks for the suggestion! Would you kindly post a sample configuration or any URL links?

Much appreciated!

Xy Le

[MHM Cisco World]

https://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/861-cisco-router-pbr-ipsla-auto-redirect.html

I found this example not exact you case but it show you how config the PBR with IP SLA to detect next-hop availability.

[Flavio Miranda]

Hi

 How are you sending and receiving prefix to/from ISPs? Are you using BGP or something else? Or static routes?

[byme88]

I am using BGP with a default route 0.0.0.0 out! Thanks

[paul driver]

Hello

As you are peering to 3 different isps from a single router then you could use as-path prepending attribute and weight.

Please review the attached file: 

[MHM Cisco World]

Since you use bgp not static route then pbr with ip sla is not proper choice for you.

Only config Local preference will do job of select isp primary and backups.

https://www.packetcoders.io/a-look-into-bgps-local_pref-attribute/

[balaji.bandi]

Adding to other posts :

there is good presentation it was old but worth looking multi-home with BGP :

https://au.int/sites/default/files/documents/31363-doc-session_7-1-_simple_multihoming.pdf

[paul.driver]

Hello

As you are peering to 3 different isps from a single router then you could use as-path prepending attribute and weight.

Please review the attached file:

[byme88]

I tried to lab this scenario up but ran into an issue of the SLA configured on the router for 2nd ISP interface. There are 2 interface G0/1 and 0/2 are already configured in HSRP using SLA Tracking DNS!

The router only has 3 Gigabit interfaces.

Thank you all for all your post and suggestion!

Byme88