Eigrp over frame relay

This may be in the wrong section, but this has to do with the eigrp over frame relay lesson here…

I have a simple question, if frame relay by default is non broadcast, how can you simply configure eigrp in the normal fashion on a point to multipoint setup and it just works?

It would make sense if you are using eigrp over frame relay that you would have to manually configure neighbors since if it’s non broadcast, it should not pass multicasts either, but in the lesson you simply enable it in the normal way and it works??

I believe this will answer your question near the bottom of the lesson. There is a piece of information that addresses this.

What it means is that frame relay is multi-access since all routers can access the network but you are unable to send broadcasts over the frame relay network. No broadcast also means you are unable to send multicast traffic. No multicast means you’ll be in trouble with routing protocols. Rip version 2, OSPF and EIGRP all use multicast. Does this mean you can’t use routing protocols with frame relay? Well no but it’s a bit tricky:

RIP, OSPF and EIGRP can also use unicast instead of multicast.
There is a method to “emulate” broadcasts over your frame relay network.

Thanks for the reply!

I had already read that lesson, but still wasn’t getting it.

The thing that always bugged me was that frame relay is non broadcast, but immediately after configuring a point to multipoint frame relay setup with a couple of spoke routers and a hub router, then your routers read “broadcast” when you look at the frame relay maps.

I understand now that this isn’t traditional broadcast like ethernet, but that it is “emulated” broadcasts in that what happens is the data is copied over each pvc, so the routing updates aren’t multicasted to the other routers, but they are copied over each pvc. 10 spoke routers would mean 10 copies, 1 update per pvc.

So, not true broadcast, but simulated broadcast.

And all of that happens with inverse arp by default.

My brain was thinking, “non broadcast means no broadcasts/multicasts, so I’ll have to manually configure neighbors every time”, but that’s not the case.

Thankfully I passed the route exam today so frame relay is in my rearview mirror!!!

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Wow I envy you I failed my route exam not to long ago :frowning: Do you have any tips for me? I seen your post a few days ago and it kept bugging me as well. Then I read it in this lesson. I had to reply Congrats on passing your route exam!


It was a difficult test. I failed it two weeks ago but not by much (758/790), so I felt good going into the second attempt. But the second exam seemed tougher. Luck of the draw I guess. A buddy at work just passed on his first attempt so it just depends on if you get questions you are more familiar with.

As far as tips, one thing I started doing in the last month or so is looking at the exam objectives and looking up white papers and other info that related to those topics from practice exams I had taken.

I took some practice exams, then noted the topics that made my stomach turn when I saw a question on them, then I googled those subjects and found (or tried to find) articles or videos that addressed those topics, then crossed those topics off from the exam objectives.

This at least helped me to get a study plan together and stick to it easier since I had exact topics I was trying to study on.

There’s an ospf chart online that shows dr/bdr, manual neighbors, timers on it. I would say know that really well, and have a good understanding of frame relay. I wrote this chart on the scratch pad they give you when you are testing just so I’d have it handly to refer to.

The failed attempt I had a 17% on L2 tech, which was frame relay. Rene’s site and some top hits when just googling for ccnp frame relay took care of the gaps I had with frame relay. But, have a good understanding of the different configs for every frame relay scenario, with and without ospf.

Unfortunately, you can never be 100% prepared for a Cisco exam as you know, since some questions will be gotten out of a 30 page white paper on page 18 sometimes!! It’s very hard to study for questions like that. Unfortunately, just remembering those questions after each failed attempt, then researching those questions after the exam will give a pretty good approximation of how deep they go on a particular subject. It’s still very stressful though.

I know this probably doesn’t help much. In the end, at least for me (cause I’m a little slow :wink: ), it took me just hours and hours of reading and videos. The two weeks between my fail and my pass I think I spent probably 50 hours easy studying. That doesn’t count the 8 months of studying prior to that!

Good luck!!

Hi Jon,

In case you are still struggling with this. Frame-relay itself is NBMA (Non Broadcast) and the only way to send broadcast (or multicast) traffic over a PVC, is to “replicate” it. This basically means that when you receive broadcast/multicast traffic on PVC1, you replicate it to PVC 2, 3, and 4.

Why does it work “out of the box”? That’s thanks to inverse ARP…

Inverse ARP is enabled by default and when it creates a L2-to-L3 mapping, it automatically adds the “broadcast” parameter that does the replication.

Hope this helps, frame-relay can be a pain and today it’s just an “exam thing” :smile:


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Rene I still needed some clarification on this so I am glad you were able to reply! I understand this much better now.