Introduction to OER (Optimized Edge Routing)

This topic is to discuss the following lesson:

Hi Rene,

I am just wondering if you have seen this technology deployed in any production networks

It sounds like a predecessor of SDN and with a great potential, but I am not sure if it has been widely deployed


Hi C,

I haven’t seen this in production networks before. The idea behind it is pretty cool, one “controller” that determines what paths to use for the network. OER however on IOS 12.4 was pretty buggy, it’s better on IOS 15 as PFR (Performance Routing).

SDN goes one step further…it’s also about configuring the network.


Hi Rene,

Any plans to do a topic on Pfr version 3 or IWAN?

Hi Purushotham,

I probably might add some extra Pfr material since it’s on the CCIE written exam, it’s not in the lab anymore though. About IWAN…I’d have to check what is included. I do have quite some DMVPN material.


Hi Rene,

I feel many concepts easy when I hear it from you. I will wait for your material on Pfr.

Thank you for the response.

Hi Rene,

are there any update about the PfR material? i am currently preparing for the written and that would be helpful.

Thank you.

Hi Andrea,

Not yet but it’s on the list.

Hi Rene and staff,
thanks for your work through the forum
Please, could you give some more explanation about the apparent contradiction below:

  1. using routes that have the same cost, OSPF can do load balancing (ECLB) on a per packet basis, that is each packet of a same flow may take a different link
  2. the router has to use CEF and CEF can’t do load balancing but only load sharing
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Hello Dominique

The two statements are referring to two separate situations. The first is referring to the use of OSPF without CEF. That is, OSPF using only process switching. This uses the CPU for all routing decisions. Under these circumstances, ECLB is achieved for OSPF.

The second situation involves a router that has CEF enabled. What is being said here is essentially that the mechanism for sending packets over multiple paths to their destinations is different. Various terms are used interchangeably, such as load balancing and load sharing, even within Cisco documentation. However, strictly speaking, when CEF is enabled, the mechanism it uses to send packets over multiple paths is load sharing. It uses algorithms that share the load (based on flows, or specific source and destination addresses) but not necessarily equally like it would with OSPF without CEF.

The following documentaiton may be helpful in further clearing this up. However, be aware of how the terms load balancing and load sharing are used.

I hope this has been helpful!


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In this lesson, I believe this is a typographical error:

For example OSPF will prefer a gigabitOER has been renamed to link over a FastEthernet link

where the text to which I added boldfacing, I do not believe should exist in this sentence.

Thank you Siobhan, just fixed this error.