ROUTE Simplified – Overview stuff, ODR

Instead of labbing my remaining topics for EIGRP from my Chris Bryant video series, as I am too mentally tired to lab into all hours of the night, so instead I started reading Chapter 1 of ROUTE Simplified. I must say, given the size and weight of this book, it has to be by far the most ironic Cisco based book ever created (Its about the size and weight of a cinder block).

So I plan to finish labbing Stub routing / static route redist / Key Chain authentication between EIGRP routers, but before moving onto OSPF videos, I think I am going to read through the EIGRP section of this book to see how it compares to the video content.

I am fried so a couple main points I took away from Chapter 1, which just overviews the coming chapters / concepts, which made me want to skip over it due to my lack of mental capacity recently after work – But I found some gems of just basics I wanted to document quick:

  • Administrative Distance determines what route to a network will be put into the route table if it receives multiple paths from different protocols, route Prefix length selects the best route from the table to that network based on how far the prefix length matches
  • Hierarchical routing consists of routers in logical groupings that can exchange information, making it more scalable with less administrative overhead (OSPF, EIGRP, etc)
  • Flat routing consists of generally routers all physically connected to eachother, network changes can impact all sides of the network, and is not scalable
  • Route Summarization has a very low AD of 5, being extremely dependable, because all more specific routes from the summary all need to be flapping for the route to flap / fail
  • ODR (On Demand Routing) is what I thought was the Layer 3 equivalent to a Frame-Relay SVC, where traffic can be routed as needed by a 3rd party, but will be charged

And On Demand Routing is actually where my brain fried and I had to bookmark it, but before I blew the fuse I got into some interesting details. It is basically an enhanced equivalent to CDP (Cisco Discovery Protocol), that operates at Layer 2, and will advertise the connected subnet on a Spoke router back to the Hub AS LONG AS NO DYNAMIC ROUTING PROTOCOL IS CONFIGURED ON THE SPOKE!!! (VERY Important note!)

However, the Hub router can run dynamic protocols in conjunction with using ODR, so it can redistribute routes learned via ODR into routing protocols such as OSPF and EIGRP. This can be particularly useful (info probably outdated) for low-speed WAN links, where updates and hellos are considerable data overhead, whereas ODR updates are considerably smaller but can still share route(s?) back to the Hub.

This is where I had to stop, as I was starting to barely write out my notes, which means I’ve hit my mental limit and I want to be fresh to wrap my head around this concept as I have a hub and spoke lab setup right now for EIGRP over Frame-Relay.

So I will try to lab the above mentioned EIGRP topics over the weekend and hammer out any ‘gotchas’ I find, then I will be back onto reading on ODR and deeper into ROUTE simplified.

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