BGP Partial vs Full Prefixes

[zekebashi]

Hello,

We currently have two active/active connections to two different ISPs. Also, we are receiving full prefixes from both service providers. We are considering changing one of the ISPs to new ISP. The new ISP is asking us whether we wanted to continue to receive full prefixes, partial prefixes, or default route to them.

I wanted to know if there are any risks in receiving partial prefixes from one ISP and full prefixes from the second ISP (keep in mind that we have both circuit in active/active and each to connected to a separate ASR).

Your input is greatly appreciated. Thanks in advance.

~zK

[julian.bendix]

Hi!

That totally depends on how much control you need over your outgoing traffic.

I personally would prefer BGP Full Table IF my resources on the Router allow it.

If you don't need a lot of control over that traffic, default route would also be fine..

Here is a good article discussing the problem:
https://aboutnetworks.net/bgp-full-routes-vs-partial-vs-default/

Hope that helps!
Best regards
Julian

[Joseph W. Doherty]

As generally longest prefix match is considered the best router, if one router only has the default, and the other all prefixes, wouldn't the latter be first choice for all?

For partial, the general approach is you only have prefixes from other ASs that have direct connections to that ISP. This works best when both ISPs are done this, but again, if one ISP provides all routes, and the other only partial routes, again, would the all routes ISP be preferred for prefixes not in the partial set?

What I've found that works very well, is taking just defaults from your ISPs and using PfR to find the "best" ISP to the destination. Think about it, all full BGP prefixes often tells us is the number of AS hops, but is the shortest AS path always really the best performing path?