OSPF Router ID's explained

[@sagarr353]

That's an great lecture, I would like you to upload another video about the major difference between Loopback ID and Router id with an great example.

[@ardentdfender4116]

I 'm studying for my CCNA currently and was studying OSPF last two days and one thing I couldn't get clarity on in my mind was understanding just understanding "Loopback address" and why it even exists. It's a lot to digest learning OSPF. So I found your video here just doing a google search. From what it seems watching and based on some things you said when a router is started up and with OSPF it seems to be instead of leaving it random to be assigned by OSPF you instead give the Router a Logical Address via Loopback Address for OSPF. In the case, if you didn't you can assign it via command #router-id x.x.x.x I guess I can still understand that in a simple way. And I'm not sure in my mind by understanding that if it gives me complete clarity as to what and why a loopback address exists.

[@RyanLindfield]

I hope you'll be relieved to hear that you're not alone on loopbacks! One of the concepts I'll throw out mid conversation and see the room flinch a bit.. Like I know "loop back" as a term, but.. why?! You've probably heard that they're logical vs physical, which means it won't go down if the signal drops / line goes down. What happens if you want to log into a router, but the IP address that you saved in your terminal software or documentation is the IP of a physical interface and for whatever reason it's down. Now what? The cool thing about a loop back is it's always up, which means, advertise it via OSPF or whatever, save it in your docs, provided that you have a redundant network that loopback should always be reachable. When things go down (link A or Link B) you can always get it because the loopback is reachable. If you're still interested: You can source alerts from that loopback, if you're collecting alerts in a database and want to search later it's advantageous to make sure all alerts come from same IP. Typically when you generate an alert you (the router) looks at the destination IP and then source IP is from the interface that you would use to get to that destination. If you have multiple redundant paths (ideal) the source could change during unplanned outages or updates, which is exactly when you want to see them. Using that loopback ensure you don't miss :) HTH!

[@ardentdfender4116]

@@RyanLindfield Thanks for the reply. The database part is a bit beyond my current understanding. However, it seems like it's a logical interface that allows connections to various interfaces even if one or two are down.

[@RyanLindfield]

@@ardentdfender4116 Yep, and a device may have dozens of IP's, which one do I want to save to connect to? One that should always work :) Database sounds scarier than it is. Splunk is the goto tool for most folks, it can be free to use if you're feeding it a limited amount of data, I think 500MB per day, but don't quote me there. Really really handy as an engineer.

[@ardentdfender4116]

Ryan Lindfield, Thanks for the reply. As well as pointing out that a Router device can have many multiple IP Address for loopbacks. It’s always good when the three “W’s” are explained in most things. Tell me the What, Why and Where. What it is, Why it exist and Where does it work. It helps to lessen the confusion in other people learning. So now a question of thought is does OSPF also work on a L3 Switch?

[@RyanLindfield]

@@ardentdfender4116 "it depends" check hardware / software ver /licensing. I've used vendors where static & RIP were free and OSPF was part of an enterprise license with IPv6 & Multicast.... $1,300 per switch to license, and they had 12 switches and no budget. Ultimately RIP got the job done and the users didn't know the difference, triggered updates and offset lists did the trick.

[@aaronmiller2877]

Ryan - I've been watching your videos about networking, vpn, etc...,and I just have to tell you - you are a great teacher. First, thanks for making these videos. Second, I was wondering if you have any more videos published elsewhere, or if you plan on releasing any more around networking?

[@RyanLindfield]

Thank you for the support! I work for Stormwind Studios teaching classes but I'll be sure to post more to youtube soon :)

[@DovaBro]

Hello I have a question: How is the Router ID helping in the DR elections? Thanks in advance