AD value for EIGRP summary route

[eric.guo]

hi all,

As we know, once we implement this command under this eigrp interface,it will suppress  more specific IP block been advertised out to eigrp neighbor. 

for example:

                              Eigrp 100

R1-interface gi 1/0--------------- interface gi 2/0 R2

we have one eigrp route as 10.8.1.0 255.255.255.0 in local routing table already on R1

when we issued the command under gi 1/0  on R1:

ip summary-address eigrp 100 10.0.0.0 255.0.0.0

so 10.8.1.0 255.255.255.0 couldn't been advertised out to R2 and only 10.0.0.0/8 can be sent out to R2.

so my question is: if we changed summary route 10.0.0.0 255.0.0.0 AD value to 100

such as: ip summary-address eigrp 100 10.0.0.0 255.0.0.0 100

so did R1 could advertise out  10.8.1.0 255.255.255.0 to R2 ? or could advertised both routes to R2 at same time? or still only advertised   10.0.0.0 255.0.0.0 ?

please let me know if possible,

thanks,

Eric

[eric.guo]

rated it , I hope I did it correctly as never rate the comments before:-)

Eric 

[Julio E. Moisa]

Thank you so much Eric,

Have a great day!

[Richard Burts]

Eric

Thanks. That does clarify what you are asking. Let me describe an experience I had with a customer to clarify when you would use the AD option for the summary address. This customer had several remote sites that connect to HQ. There was an Edge router that had the connections to the remote sites and had a connection to the core router. The Edge router was learning a default route from the core router. The design for the network was that the remote routers did not need to learn all of the subnets from HQ and from other remote sites but only needed to learn a default route from the Edge router. So the Edge router configured summary address 0.0.0.0 0.0.0.0 on the interfaces that connect to the remote sites.

But the result of this was that the summary address on the Edge router generated a route for 0.0.0.0 with AD of 5 and that was inserted into the routing table and replaced the default route learned from the core router. So now the Edge router has a default route saying that the next hop is Null 0.The solution was to use the AD option on the summary address command so that the generated summary had an AD higher than the route learned from the core. The result was that the summary 0.0.0.0 was advertised to the remote sites but was not inserted into the routing table of the Edge router allowing the Edge router to use the default route advertised from the core.

That was my experience of using the AD option in the summary address command. 

HTH

Rick

[eric.guo]

nice! this is exactly I am looking for.

thanks Richard!

and thanks Julio as well!

Eric 

[Richard Burts · Accepted solution]

Eric

I am glad that my explanation was helpful. I agree that the optional parameter for AD in the summary address command is not easy to understand at first. But there are some circumstances where it is needed.

HTH

Rick

[Richard Burts]

Eric

After posting my response I read your post again and am a bit confused. You ask this "for these more specific routes such as : 192.168.0.0/24". How does 192.168.0.0 get into this question? You were asking about summary address 10.0.0.0 255.0.0.0. This summarizes any more specific routes in the 10 network but has no effect on 192.168.0.0 networks. So can you clarify what it is that you are asking?

HTH

Rick