Finishing EIGRP (for now), Starting OSPF

So after such a long break from studying, I am finding I am way out of practice, and trying to stretch my studying across too many materials is slowing things down to a complete stop – So I decided I am going to put the ROUTE Simplified book down for now, and go through it in it’s entirety after going through the Chris Bryant video series – I just absolutely love that guys dry sense of humor. I’ve tried INE’s CCNP course for a video, and I cannot get into the instructors teaching style at all, which is a shame cause I thought Mark Snow did an excellent job with his CCNA Voice course he offered free on INE.

Anyhow, I was working with default route redistribution, and found myself getting brick walled working with the “ip default network” command. I was adjusting ip route statements, adding and removing the default route to be redistributed in router configuration, and it just was not propagating to my two spoke routers – I even turned on R4 for this that connects off R1’s Serial0/1 interface. So I’ve had no problem using the “redistribute static …” in router configuration to propagate default routes to the spokes, but I just couldn’t crack the ip default network command. After spending enough times reading Cisco documentation on it and looking at forums, it seemed like there were too many reports of it working weird or buggy in certain IOS versions (some version of 15.x code I believe?), and I’m running mostly variations of 12.4 code on my routers. So admittedly the buggy behavior may not be affecting my IOS versions, but it was just stopped forward progress with studying so I skipped over it and moved on to the final parts of EIGRP – Stub configurations / Interface Authentication.

Stub networks I felt was just glossed over in my video series, so I am hoping the ROUTE Simplified goes more in depth with this topic, because I can configure it (I believe) correctly and maintain all adjacencies to EIGRP neighbors but I fail to really grasp why you would even bother making an EIGRP router a stub. I moved from this topic after configuring it and understanding theoretically why one would use Stub routing, but I fail to see why you wouldn’t just set a default route back to the Hub router and call it a day for more practical purposes? I feel like I may not be really digging into that topic as much as I should, but it was covered so briefly I am not sure how much that mattered, so I just continued on to authentication.

When I was configuring key chain Authentication on my lab Friday I wasn’t even looking at notes as to which debugs to run to see what was going on, or looking back to see the syntax for the interface level “ip authentication mode… ” and “ip authentication key-chain …” commands, which reaffirms covering the CCNA material over the winter did pay off… somewhat. I actually had trouble getting the neighbors to drop the adjacency as expected when a key was mismatched or not present on that interface, this was my one hang up, but I pretty quickly found that I had just skipped over the above mentioned “ip authentication mode …” command that is also required on the interface to ‘activate’ the authentication.

I’ve already gone over, and heavily noted, the base theories of OSPF in my video course. Particularly things like how DR / BDR elections use the highest interface Priority first to elect a DR / BDR, followed by the highest loopback, then physical interface, unless you enter the “router-id x.x.x.x” command in router configuration mode to manually set the RID which will take precedence over Loopback and Physical interface IP’s (but DOES NOT override interface Priority in election process).

Though some finer points in the theory and operation of elections and updates for example is that topology changes are multicast to that only the DR and BDR listen by the router detecting the change, they run the SPF algorithm against their OSPF database, then another update multicast of LSU’s containing the LSA are sent to which is an “All OSPF” listening address by the DR while the BDR just updates itself hoping to some day get promoted to that DR Role (though we don’t want that)! Another thing I had either forgotten or was not covered, is that the DROther (non-DR / BDR OSPF routers) send back an LSAck (LSAcknowledge) back to the DR as a receipt or confirmation that the update was received.

Now to get to backing up those running configs, resetting the routers, and then I am done with CCNP related things for the night! Time to get some OSPF going on and I will no longer have to work with sub-interfaces to avoid split horizon hampering my propagation, I don’t know what I’m going to do with myself working with .1 / .2 / .3 again for my WAN IP addresses!

Big update there, I admittedly don’t get on here the day of studying like I am going to try as I venture into murkier waters of BGP, Redistribution, and IPv6, but I shall be back to keep this party train moving forward to finally earn that CCNP I set out to earn years ago!

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