FULL BGP vs POLICY ROUTING

[mwhitlow]

All,

I've been working with BGP for 14 years and have deployed many implementations in multi-homed environments with full Internet BGP tables.

I've had conversations with various people lately about using policy based routing instead of the full BGP table, mostly due to hardware limitations.

I understand how I would configure this if I wanted to do it, but what I am not understanding are the pros and cons of the FULL BGP TABLE vs POLICY ROUTING. What am I loosing if I go with PBR vs the tried and tested full BGP table?

Thank you much

Mike

[Jon Marshall]

Mike

You are primarily losing the ability to influence traffic coming into your AS. PBR will allow you to determine which path traffic takes when it leaves your AS although at a higher cost of configuraton in many cases ie. you can easily apply manipulate attributes received from a specific neighbor with BGP but the route map config to do do the equivalent with PBR would be a lot more i would have thought.

But in terms of outbound from your AS you could with both BGP and PBR achieve the same next hop.

But you have no way with PBR of influencing inbound traffic. eg. where you would use MED or AS prepending there is no equivalent in PBR that i am aware of. In addion community attributes where you may not want your routes advertised further than the next hop etc. would not be possible with PBR.

That said, an awful lot of sites that are mutihomed often don't need either a full routing table or PBR so there are definite arguments as to whether a full routing table is always the best case.

Note also i haven't worked for an ISP so the above may be completely different in an ISP environment.

Jon

[Joseph W. Doherty]

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Posting

Mike, when Cisco's OER came out, (for multipath egress) I really wondered what benefit full Internet routing tables provided vs. it.  Well, I found OER seemed to work much better.  I switched a pair of my Internet routers (3845s with DS3) to it and just defaulted to each ISP.  OER did dynamic egress load balancing, and with its passive monitoring, it also did dynamic best performance to the destination rerouting too.  OER's impact to my routers was much, much less than the full BGP tables.

So, you might also consider PfR (i.e. OER v2), if your equipment supports it.  Possibly a superior solution to full BGP tables and/or manual PBR.

[paul driver]

Hello

Sending and accepting a Full BGP table no doubt incurs router cpu and memory resource, Even if the accepting CE router filters on  the SP advertised routes  are still crossing the wire and being processed by bgp.

As JON has mentioned if the customer can get away with receiving a default route or partial routes if would be more applicable and less resource intensive.

Saying that if a full bgp is being sent and it isnt required I suppose BGP ORF could be implemented to resolve the unwanted routes from crossing the wire in the first place.

In terms of PBR and route manipualtion for SP ingress traffic I am on the understanding it will not applicable anyway.

res

Paul

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Thanks.

[sathvik k v]

I agree with Joseph, PFR is a better solution

Regards,

Sathvik