EIGRP stub router generates default route

[Difan Zhao]

Hi experts,

I have a EIGRP stub router R1 and now I need to add another router R2. The R2 only needs the default route so I was simply configuring the R1 to generate a default route on the interface connecting with the new router. however that doesn't work. The command I used is

ip summary-address eigrp 1 0.0.0.0 0.0.0.0 255

What I found out is that when I change the AD to something lower than the AD of the learned default route (there is one EIGRP router redistributes the default route in the EIGRP domain) then it would work however as you know this overwrites the default route learned on R1

I just want to know if this is normal or did I make a mistake? Is there any reason behind it?

Thanks,

[cadet alain]

Hi,

you set the AD to 255 so the summary won't be installed in the routing table.

Regards

Alain

Don't forget to rate helpful posts.

[paul driver]

hello cadet-Alain

I was on the understanding the AD of 255 removes the discard from the router that is advertising the summary?

is this not he case?

Res

paul

[Difan Zhao]

I know but the question is why it doesn't generate a default route

Thanks,

[paul driver]

Hello Difan

With R1 as a stub router it should not have any other neighbours other than its hub eigrp neighbour

This stub feature is suppose to  prohibit advertising routes learned from its hub to another peer, thus r1 will not become a transit router for R2

as for lowering the admin distance the lower value will take precedence and what you are doing is summering a default to R2  thus a it will add a discard to R1 towards R2

Hope this make sense?

Res

Paul

[Difan Zhao]

Thanks Paul. I understand that this is a bad approach but I just want to understand how this works. Please note that the router can still generate other summaries even with AD set to 255. It just doesn't generate the default route.

I want any of you to try this scenario

R1 --- R2 --- R3

You configure the R1 to redistribute a default route. Make R2 and stub. Then on R2's interface to R3, configure a normal summary (maybe for some loopback interface subnet) as well as a summary of a default route.

What I see is that I only see the summary of the loopback but not the default one on R3. That makes me think that there maybe a mechanism to prevent stub router from generating default route... I just want another person to confirm that you see the same, not a mistake or something I missed...

Thanks,

[paul driver]

Helllo

That is correct as stated previous r2 set as stub will prevent the re advertisement of any routes it receives from r1

Res
paul


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