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John Blakley

PFR Understanding


I've been playing around with PFR and trying to get an understanding of what I'm supposed to be seeing. I have a 4 router setup: 1 "ISP", 2 Border routers, and an internal router (MC). I have a loopback configured on ISP router My BR1 is configured for a max-xmit-utilization of 2 percent and BR2 is just left at default. The MC has BR1 configured for throughput and delay and BR2 the same. BGP peering to ISP from both BRs and BRs to MC is iBGP.

What I had seen this morning was that pinging from the MC with a large size and high repeat count allows for the MC to notice that it's OOP. I was under the impression that OER changes the routing table by either changing local pref or prepending AS numbers. What I had seen was the the MC changed it's local-pref for the route to 5000 to BR1 and changed the route out to BR2. This was fine, but the return traffic from the ISP was coming back through BR1. It didn't seem like the MC changed anything at the BRs. Any ideas? Shouldn't I be seeing the change on the AS path at the ISP router? (this was in gns)



HTH, John *** Please rate all useful posts ***
Joseph W. Doherty
Hall of Fame Expert


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John, I've never used PfR's inbound load balancing, but recall it requires extra config beyond what's needed for outbound load balancing.  Are you sure you're properly configured for inbound load balancing?

Dan-Ciprian Cicioiu
Rising star

Hi John ,

I think that by default PFR is used for influencing the outbound traffic.

In order to influence the inbound traffic there is a feature BGP inbound optimization

"The PfR BGP Inbound Optimization feature introduced the ability to support inside prefixes. Using BGP, PfR can select inside prefixes to support best entrance selection for traffic that originates from prefixes outside an autonomous system destined for prefixes inside the autonomous system. Company networks advertise the inside prefixes over the Internet using an Internet service provider (ISP) and receive advertisements for outside prefixes from an ISP."


This was for outbound traffic from the perspective of the MC to the loopback at the "ISP". The ISP is peered with ebgp and the BRs are peered with the MC with ibgp. I attached a diagram that I probably should have attached earlier

The problem that I have is that I was seeing the MC with a local pref of 5000. I was under the impression that the MC is supposed to make the change at the BRs. I also thought that I would see the bgp table on the ISP ( with a prepended path from BR1 after it did the switchover to BR2, but that didn't happen.

HTH, John *** Please rate all useful posts ***

Hi John ,

This was fine, but the return traffic from the ISP was coming back through BR1. It didn't seem like the MC changed anything at the BRs.

I understood from your initial post that you saw that PFR changed the local pref of the ISP's loopback ( ) to 5000 (which is the default value for the local pref, but also for the tag used on static routes ) and your issue was related to the traffic coming from the ISP to the 'client' ( which is the inbound traffic ).

As far as I know PFR influence the BGP preference only using local pref ( outbound ), and also by default it doesnt do anything regarding the incoming traffic.

Did I undestood well your issue, or was regarding the fact that you want to see prepended the ISP prefix in the 'client' network ?



The MC changed it's local pref to the prefix to 5000 in its bgp table to point to BR2. The ISP still showed it's return route to the MC subnet through BR1, so in essence it was looping. Does that make sense? I'm going to play with it some more tonight after work and see if I can make any sense of it.

Oh...after reading your you're saying that the MC was doing it's job by changing the path outbound but it doesn't change anyone's routing table on the outside of the network...I think I get it. I think ....

HTH, John *** Please rate all useful posts ***

Yes. The main job of the PFR is to measure the performance of the local network - from the persepctive of the border routers - to reach the destination. So it will influence the outgoing traffic based on some defined parameters.

It seams that there is feature , that will influence also the incoming traffic : PfR BGP inbound optimization, which will do prepending on the prefixes advertised.

Have a look at this doc :