BGP Multiple ISP VR Requirements

[KyleFreise]

I'm attempting to wrap my head around a very critical piece of setting up BGP between 2 ISP's concerning how many Virtual Routers are required.

I currently have 1 ISP (A) up and running on BGP just fine and my other ISP (B) will be converted to BGP on Monday.  Both will be advertising my public IP space from ARIN.

So my question is, do I put both ISP A's and ISP B's interfaces on the same VR or do they need to be on their own separate VR's?

I'm receiving a few conflicted answers to this question, so I'm looking for real world experience.

Currently I'm still a strong believer in that I need to just add my ISP B as its own Peer Group to my current primary Virtual Router, add ISP B's own subinterface to the Resdistribution Profile along with ISP A's subinterface, configure a new Import Rule for ISP B plus an Export Rule with a Prepend of 2 if I choose to, and finally check ECMP for "load balancing".

All this sounded great until I was told the following from a Palo rep: "Two interfaces ( belonging to same VR ) cannot have IP addresses from the same subnet. x.x.x.x/24"

That threw a wrench into my whole thought process because both ISP's are advertising my /24 from ARIN, but are physically connected with 2 different /30's to each ISP's switch.

[pankaku]

You can have one VR. Prefer one BGP peer and if that BGP peer goes down then it will automatically start using second ISP

Check this KB

https://live.paloaltonetworks.com/t5/Configuration-Articles/How-to-Prefer-a-BGP-Peer-for-Installing-...

[KyleFreise]

My import rules are default routes (0.0.0.0/0) so wouldn't ECMP be a better model for load balancing?

I do agree now though that a single VR is all that is required.

[pulukas]

If you want to load balance then your options are to use ECMP (if you have PanOS 7 where this feature was introduced) or configure policy based routing.  With policy based routing you choose what types of traffic by source or other criteria to forward to which ISP.

ECMP

ECMP Load-Balancing Algorithms

Configure ECMP on a Virtual Router

Enable ECMP for Multiple BGP Autonomous Systems

Policy Based Routing

[KyleFreise]

I tied each ISP's BGP link into one VR and what I was originally confused about was how to tie our /24 ARIN space in with these links.

In short I didn't realize you can apply the /24 public space to any interface and just advertise it out with the Redistribution Profile.  I was thinking it had to be applied to both external ethernet ports.

Not the case, just tie the /24 to one of the external facing ports as subinterfaces and then I put a simple /32 on the other ISP's subinterface for ping testing.  Not really necessary, but I was playing around.