How to configure Redistribution between EIGRP and RIP

(Rene Molenaar) #1

This topic is to discuss the following lesson:

(system) #2

This is probably the most amazing explanation I have come across in my process of certifying as CCNA. It’s simple, straight to point and easy to understand. I’ve always thought that switching and routing isn’t difficult to understand, it’s just awfully explained by lecturers and people in general but you definitely got a talent to make complex things easy. Keep it up.

(Rene Molenaar) #3

Thanks Ivan! I try to keep things as simple as possible. For a demonstration of redistribution you don’t need more than 3 routers :slight_smile:

(system) #4

Ahh! This is simply awesome Rene.
I have come across your lessons. They are so easy to understand. Keep it up.

(Rene Molenaar) #5

Thank you Basan.

(system) #6

thanks for the explanation… this is also what I know about rip-eigrp redistribution…
however, I came across a website that used a different method of making AD=12 for eigrp routes in RIP… using the command: distance 12 network netmask
you have any clue about this… got me confused what the real method is
thanks in advance.

(Rene Molenaar) #7

In my example there is only 1 router that is running EIGRP and RIP at the same time. When you have two routers doing redistribution, it is possible that you get a scenario like this:

Prefix from routing protocol A > B > A

This is a problem that can cause routing loops or sub-optimal routing. Imagine that we have prefix 192.168.1.0/24 in EIGRP, by default it has a AD of 90.

Once it is redistributed into RIP, it has an AD of 120.

When we redistribute it back into EIGRP, the AD is 170 (external).

Since 170 (external) is higher than 90 (internal), EIGRP will never prefer a redistributed prefix over an internal route.

RIP doesn’t have this “failsafe”…when you redistribute into RIP, the AD is always 120. We can change the AD ourselves to solve some problems.

Besides the AD, we can also fix redistribution problems with route tagging and changing metrics. In the beginning it might be very confusing to understand so try to focus on the problems of redistribution scenarios and then see if it can be fixed by playing with the AD, metric or tagging :slight_smile:

Rene

(Deepak M) #8

Hi Rene,

Why the below command is not used here ? its being used in ospf->rip redistribution.

R2(config)#router rip
R2(config-router)#default-metric 5
(Rene Molenaar) #9

Hi Deepak,

You can set a default seed metric globally with the “default-metric” command. That’s what I used for RIP in that example.

It’s also possible to specify the seed metric when redistributing. For example:

R1(config)#router rip
R1(config-router)#redistribute ospf 1 metric 5

This will accomplish the same thing.

Rene

(Deepak M) #10

Hi

Understood. Thanks a lot!

Deepak

(Stanislav P) #11

Hi Rene, what is the name of the program you are using in this video - looks very good i would like to try it.

Thanks :slight_smile:

(Wisam A) #12

Hello Rene,
Thanks a lot for you amazing explanation,
I still have a question how to decide what is the value of K1 to use.
or if I need to troubleshoot the K1 value if it’s correct or not, what to look for?
Thanks in advance.

(Lazaros Agapides) #13

Hello Wisam

In general, the default values of the K metrics should not be changed. They are configured so that EIGRP will function correctly under the most common circumstances. However, if there is strange behaviour on your network or if you want to configure an elaborate routing behaviour, then K1 as well as the rest of the K values can be adjusted.

K1 can be set to anything between 0 and 256 (yes, 256, not 255) as can all of the K values. Specifically, K1 involves taking into account the minimum configured bandwidth between the router in question and the destination network. If K1 is 0 then the bandwidth is not taken into account. This would not be a good idea if you have links in your network with widely varying bandwidths. If K1 is greater than 1 then, the bandwidth will be taken into account much more than the rest of the K values.

You can find out more about this in Rene’s lesson on EIGRP K Values.

I hope this has been helpful!

Laz

(navraj c) #15

Hi, Can someone please explain why need to define metric when we are doing redistribution, I know it will not restribute the route if we don’t use it but i am not sure what the concept behind it, can someone please help to clear that.

(Lazaros Agapides) #16

Hello Navarj

RIP and EIGRP, although both distance vector routing algorithms, use very different metrics. RIP uses a number between 0 and 16 which indicates the number of routers, or hops, between the current router and the destination. EIGRP uses a complex composite metric that is derived from a formula from which the metric is derived. This metric has a range from 0 to several million.

So you see that the metric used by RIP is incompatible and essentially meaningless to EIGRP and visa versa. For this reason, when a route is redistributed from RIP to EIGRP for example, you must specify the cost to that route using metrics that EIGRP can understand. The same goes for redistribution in the opposite direction.

I hope this has been helpful!

Laz

(navraj c) #17

Hi Laz,

That make sense thank you for helping, I have another question what matric we need to define how we know that, it can be anything random?

When we advertise OSPF in EIGRP at that time we have to specify OSPF metric why we have to, I know it will not advertise the route if we don’t do that but what is the logic behind it and how we know what values should be best for it to select.

Navraj

(Lazaros Agapides) #18

Hello Navraj

You should choose the values that you will use for the metric when redistributing very carefully. These values will affect the way the routing protocol will interpret these routs, and thus will choose which routes to use. When redistributing into EIGRP, keep the following in mind:

Bandwidth - The bandwidth you use is probably the most crucial. Here you are stating what the lowest bandwidth is between the current location and the destination. If you generally have a high speed network with gigabit or 10gigabit links, make sure this is set appropriately. Remember, these values must be comparable in order to make a redistributed route have an appropriate metric to be used.

Delay - This value is also important because it too has to do with the speeds of interfaces that exist between network equipment. The lowest value is 10 microsoeconds, which corresponds to GigabitEthernet speeds. If only smaller links are available in your network, this should be tweaked to be comparable to those.

The other K values are not used by default, but if you choose to use them, then make sure that load, which can have values between 1 (low load) and 255 (high load) should be set low, and reliability also between 1 (low reliability) and 255 (high reliability) should be set high. The MTU configuration should remain at the default of 1500 as this does not affect the routing decisions.

I hope this has been helpful!

Laz