Conditional Advertisement & Remote IP Monitoring Questions for Dual ISP Setup

[Austin_Mascarenhas]

Hi all,

I’m working on a dual-ISP BGP design on a Palo Alto firewall and I have a few questions regarding conditional advertisement and remote IP monitoring. Here’s the scenario:

• I have two ISPs: ISP1 and ISP2.

• I want to advertise a specific IP pool to ISP2 only if ISP1 stops sending a default route.

• Ideally, ISP1 should be preferred for outgoing traffic when available.

Questions:

1. Conditional Advertisement on Default Route:

   • Can conditional advertisement monitor just a default route from ISP1 and start advertising the IP pool to ISP2 only when that default route disappears?

2. Advertisement Still Going to Both ISPs:

   • In my testing, the IP pool is still advertised to both ISP1 and ISP2, even if ISP1 stops sending a default route.

   • Is it possible to suppress advertisement to ISP1 entirely based on the conditional advertisement?

   • If not, what is the recommended solution for this scenario?

3. Remote IP Monitoring Approach:

   • Should I enable remote IP monitoring on both ISP1 and ISP2 by adding a /32 static route toward the remote IP being monitored?

   • The goal is that when the monitored IP stops responding via ISP1, all routes from ISP1 would be removed.

   • If this is the correct approach, then I could:

     • Accept default routes from both ISP1 and ISP2.

     • Assign higher weight to ISP1 for incoming traffic.

     • Use AS path prepending when advertising the IP pool to ISP2 so that ISP1 is preferred for outgoing traffic.

I’d appreciate guidance on whether this design approach is feasible and the best practices for conditional advertisement and remote IP monitoring in this scenario.

Thanks!