Intro to Policy Routing (PBR) and Local Policy Routing, new Topology soon!


This will be the intro to the pointers or theoretical stuff to know before diving into configuration and troubleshooting. On Chris’s initial Topology he has 3 routers connected on one common subnet, so I will need to review the configuration’s to understand what the actual networks are or if there is a reason he did that, so stay tuned for a Topology update.
There are quite a few VERY important details to PBR, and I don’t want to them to get lost or buried in sentences, so here are the facts on Policy Routing and Local Policy Routing:

  • Policy Routing does not effect the final destination of traffic but rather what path it takes to get to that final destination
  • Policy Routing applies to incoming traffic to the router, Local Policy Routing is working with traffic that is created on the local router itself, not incoming traffic
  • If configured on a specified interface, it will only effect traffic incoming traffic to that interface and leave all other traffic to the normal routing process
  • Can route based upon both source address, destination address, etc, so Extended Access-Lists are usually the most effect way to achieve Policy Routing

The next two I need to group together for clarity sake as to why they belong together, but I advise, but you may need to read the next one a couple of times for it to really sink in:

  • If traffic DOES NOT match any permit lines in a route-map, but DOES match a deny line, that traffic is sent to the routing process for normal routing
  • If you want traffic that DOES NOT match any permit or deny lines in the route-map to be discarded and not sent to routing process, you must create a catch-all clause at the end of the route-map sending traffic to Null0

That is it for tonight, I will update once it is configuration time!

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