Cisco Redistribution & Routing Loops
HTML-код
- Опубликовано: 6 фев 2025
- Learn how to master mutual redistribution and identify potential routing loops very easily. The example, OSPF to EIGRP mutual redistribution has the potential to create a routing loop through the existence of an advertisement loop.
![Felix "Unfair" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/Oswujxm2Ag0/mqdefault.jpg)
![BLACK BAG - Official Trailer [HD] - Only in Theaters March 14](http://i.ytimg.com/vi/Du0Xp8WX_7I/mqdefault.jpg)
10 years later, still worth it men. Studying for the ENARSI and I was not seeing a lot of documentation about loop without RIP.
thank you so much for your time.
Excellent video, wish I stumbled across this when I was first studying redistribution.
Best video I've ever seen on this topic 👏
Great visual explanation. The two questions are very useful in redistribution design and came in very handy for the ROUTE exam. Thank you for sharing.
Yeah, all these redistribution videos have helped me a lot. I very much appreciate it. It's helped me understand much more. :) AD is definitely important when you want something to show up in your routing table as opposed to something else.
The best I have seen so far. Probably it is missing the prefix filtering solution.
Great video!! Step by step and slow enough to keep up thank you for sharing your knowledge.
Thanks Brian, Good Job, just one statement "if then...else " to cover the main idea about redistribution. you did a job. we'r still waiting more videos as you'v promise for other technologies, other network stuff.
Very good video, really cleared redistribution questions...
Really good and clear explanation. Thanks for your time.
The redistribution does not look inside a routing process, it looks at the routing table for the routes to be considered for redistribution.
thank you so much Brian, this video was so helpful to understand route tagging. the examples were very easy to understand. I ran my own topology on GNS3 to make a similar configuration and it works perfecly :D
your videos are really great please make some more !!
Just to say thanks for you explanations ..your time and your efforts...
Any plans to upload more videos? I can't get enough :)
Nice video, good explanation. Thanks
For EIGRP, equal cost load balancing will take over and depend on your CEF per-packet or default per-destination load balancing. But, both routes will be installed, which means the loop is still present.
It all depends on how you want traffic routed. If you set the AD to 171 on OSPF then External routes coming from the EIGRP to OSPF domain will have an AD of 171 and not be believed as better through the OSPF domain. The E1 E2 OSPF routes going to the EIGRP domain will be believed as better through the EIGRP domain by the ASBRs. Follow the AD and you'll see how it matters. It really affects how the ASBR routers route through their own domain or through the bordering domain.
HI Brian, You have explained a trivial subject for me, thank you just one question, wouldn't shutting the interface shut down remove the route from the original router and hence from the redistributed routers also, so If I shut the lo0 70.X.X.X.X on R7 then it would remove the route from the table of R7 and hence no longer be advertised as an external route to R4 or any other router for that matter,, i hope I make any sense....but i thought removing the interface will remove the LSA also..
thanks in advance Sid
In the video I didn't show that R2 had better redistribution metrics. The problem will still be there though. If R2 has worse metrics and the route disappears from R1, R2 will immediately be chosen and the loop will begin. Always track where your routes are coming from, but also track what other routes exist in the topology table, there may be a routing loop lingering, waiting to make itself known.
Thanks for all of the comments. Keep looking forward to other videos, and I will post more next week after I take the lab.
I just designed a very advanced BGP redistribution and will share the detailed information about BGP redistribution here in a few days.
Thank you for the very informative video, I could watch stuff like this all day long. :) I was still wondering a little about why you bothered to make AD 171 in the first place. I watched another redistribution video on RIP to OSPF redistribution, and not only did there have to be tags in place, but the AD for OSPF had to be changed higher than the the RIP AD of 120 in order for there to not be a traceroute issue. So the only thing that needs to be done with this is route tags right?
Hey man,
Thank you very much for the video, it was very informative!
Just a doubt, these "2 questions" rule is used also on EGPs ?
I mean, a router running eBGP would ignore a route coming from OSPF if it already has a route to the advertised network?
I have a scenario like that and the route running OSPF and BGP is prefering the route from OSPF and beyond that, it is redistributing the OSPF route to the whole BGP network.
No changes on the ADs were made.
thanks!
Thank you for this - very good explanation.
It's never too late to say "Thanks You!!"
you are freaking awesome man, good job. I ' really appreciate you video's
thank you!! great explanation it helped me alot
Thanks a million for this!
Picked up some skills along the way.
Brilliant on the tagging number of 110 and 170! :D
It would be good if you can also share out the Dynagen/GNS3 network file for the convenient of us. :-)
great and helpful video. thanks
Hi Brian.
Your video is pretty good. One question is with tag, it looks like one of the router learn the best route from ospf instead eigrp becuase ospf AD is 110 and eigrp external ad is 170. RishiRap also mentioned in his comments. I was wondering what is the best way to solve this issue. Can we change the ospf external type route ad to 171 to fix it? router ospf 10
distance ospf external 171
Thanks
you could selectively raise the AD of the EIGRP route192.168.18.0/24 in the ospf domain to 171 and leave the rest of the external OSPF routes at AD 110. Now R2 and R3 will believe the route through eigrp only because AD 170 and will believe the 70.0.0.0/24 network via ospf. What do you think?
do this on R2 and R3
access-list 1 permit 192.168.18.0 0.0.0.255
router ospf 1
distance 171 0.0.0.0 255.255.255.255 1
It's whoever gets there first. R2 in this example has better metrics announcing the 18.0/24 back into EIGRP. EIGRP on R2 will not hold the route from R1 and therefore will not have anything for R2 to put back into OSPF. If R2 were to redistribute faster than R3 the opposite way, then R3 will not have the route and R2 will be the only router to announce 18.0/24. It's all about the EIGRP side.
One of my friends has a blog post dedicated to this topic, I hope along with this video, that post will also help people understand it in a better way,. Here it is :
Also, you did your route tags way more complicated than this other guy did, he did it a much easier way. Just wondering if you know of the way he did it. route-map deny 10
match tag 7
route map permit 20
set tag 7
This is set for both RIP and OSPF redistribution along with a change of the AD metric in OSPF on all routers to 170 for external routes.
I also tried the lab. Tagging did not work to resolve the issue as RACING Condition occured and ospf LSA5 with AD 110 replaced the eigrp route on one of the redistributing router. so I could still connect to the eigrp dest network in a sub-optimal path.
I fixed the issue by assigning AD of 171 to select routes from eigrp using "distance access-list" command. under "router ospf" process.
+RishiRap
Hello
why you need the accesslist to pick up route? Can not you change all the route to 171? Will this cause any issues?
router ospf 10
distance ospf external 171
Thanks for this video!
That actually will not do much for you. All CCIE material states the solution I present as a correct multi-point redistribution solution. I just take it a bit further to show how some solutions out there, setting the AD only, is not correct.
I guess ospf external administrative destines for redistribution is 20. and eigrp is 170
Ospf maintains the same AD, but when redistribute routes inside of the process, the protocol marks the routes as External Type 2 (by default) with an AD of 110 and a metric of 20
Hi, What software you are using for drawings?