PfR with 1 router and 2 links

A co-worker asked me about PfR today. I’ve been researching it for a couple of weeks for an install that I might use it with. His customer has one router and two internet connections. They would like the traffic load balanced. From (what little) I know about PfR I didn’t think it was possible. When I read the config guide, one of the things where you can insert intelligence is link utilization. You configure PfR so if one link hits 90% utilization it will start sending traffic to the secondary link. Well that wouldn’t really work here because we may never have 90% utilization on the link. Either I didn’t understand it correctly or it was incorrect. When you configure the utilization in PfR, that is when it starts to load balance. So if we set the utilization on the 100mb link to 25% it will then start to load balance. That’s closer to what we want. It’s not perfect load balancing, but in this case it is acceptable since the first circuit (labeled WiscNET) is a more stable connection.

So for the test I set the link utilization very low so I could trigger PfR with just ICMP traffic. I ping’d 1.2.3.4 from 192.168.1.10 with 5000 packets at a size of 1490 datagrams. I ran some debugs-
%OER_MC-5-NOTICE: Range OOP BR 6.6.6.6, i/f Et1/0, percent 100. Other BR 6.6.6.6, i/f Se2/2, percent 0

In red we see that PfR prefers to go out the Ethernet interface. That is as expected. It sees that the Serial link is available but no traffic (percent 0) should go across it.

%OER_MC-5-NOTICE: Load OOP BR 6.6.6.6, i/f Et1/0,  load 1500 policy 50
%OER_MC-5-NOTICE: Exit 6.6.6.6 intf Et1/0 OOP, Tx BW 1500, Rx BW 1500, Tx Load 100, Rx Load 100
Above is some of the policy info.
%OER_MC-5-NOTICE: Range OOP BR 6.6.6.6, i/f Et1/0, percent 100. Other BR 6.6.6.6, i/f Se2/2, percent 2
Here we can see that the Ethernet interface is using 100% but is also sending 2% out of the serial interface. 
Let’s take a look at the interfaces and see what they look like.
Ethernet1/0 is up, line protocol is up 
  Hardware is AmdP2, address is aabb.cc00.0101 (bia aabb.cc00.0101)
  Description: Connection to WISCNET
  Internet address is 2.2.2.1/30
  MTU 1500 bytes, BW 1500 Kbit/sec, DLY 1000 usec, 
     reliability 255/255, txload 255/255, rxload 255/255
Whoa! This is a 100Mb Ethernet connection but it’s showing  100% utilization. I’m not pushing that much traffic (remember I’m just pinging). I would assume PfR is manipulating the load, but I’ll have to dig a little deeper and find out. Let’s move on to the serial interface.
Serial2/2 is up, line protocol is up 
  Hardware is M4T
  Description: Connection to Charter
  Internet address is 1.1.1.1/30
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec, 
     reliability 255/255, txload 4/255, rxload 1/255
Here we can see the load is a little under 2%.
That matches the debug output above.
%OER_MC-5-NOTICE: Range OOP BR 6.6.6.6, i/f Et1/0, percent 100. Other BR 6.6.6.6, i/f Se2/2, percent 2
Excellent PfR is working. This is a pretty simple example and credit goes to marwanshawi on the Cisco Support Community.
https://supportforums.cisco.com/docs/DOC-8353
Other good links
http://docwiki.cisco.com/wiki/Performance_Routing_FAQs
http://docwiki.cisco.com/wiki/PfR:Technology_Overview

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