EIGRP

[eandrcisco007]

Gentlemen,

I am planning to change the Subnet id /Mask of one of our back up router's interface and I was wondering if that could have any negative impact on EIGRP route and its convergence and if it could stop advertising static routes to other router/switches running eigrp...

Basically I am trying to be proactive to know what to expect and what I am going to see and deal with in order to be prepared and come up with plan B.

Is there anyone that have gone through the same path or any experiences in this regard to share please?

[eandrcisco007]

Yes, it says " EIGRP-IPv4 <1> : Neighbor ............ not on common subnet for gi 1/1 "

it repeats the same message twice for two different IP address...

and like i mentined, the routers are working great with the new Subnet ID/Mask without connecting switches...!

[christopher jardine]

are the switches on different subnets?

are you using the switches as layer3 switches?

[eandrcisco007]

Yes and yes.

[christopher jardine]

so that's your problem,

i don't know your entire setup but here's a demonstration.

R5 and R6 are on the same subnet so all routes are propigated.

R8 has a mask to where R5 and R6 are not on it's subnet.

is that like what your setup is.

if it is if you change the subnet mask of R8 to match it will fix the problem.

this is just an example but it definately demonstrates the "not on common subnet" error

[eandrcisco007]

it is pretty much yes...and thank you

At this point, changing the R8 Subnet mask is not an option so i have to find away to make it work...

[christopher jardine]

Static routes?

[eandrcisco007]

well... thank you....i have thought about it earlier but i i am not sure... i will have to look into it in details if feasible at alll... 

basically eigrp sub. mask should match any other mask or else it is unable to advertise different subnets... which is a draw back...!

[christopher jardine]

what about this, can you change your mask so the router getting the "not on common subnet" error atleast has the routers on it's network?

here's an example of what i am talking about:I tested this and R7 was able to get the static routes and the "not on common subnet" was cleared up.

[eandrcisco007]

Hey Chris,

Thank you, this is a great solution and even though your point is valid but i am unable to make any changes at this stage,

The subnetting issue is mainly a design issue that canot be changed over night specifically since all is  working great but at the same time I am trying to find a solution to make it happen with a least possible breaks and down time,

I am trying to bring both routers on the same subnet for future changes and for a faster network convergence with minimal delay if pssoible at all...

[christopher jardine]

Yeah i was just throwing that out if it was anyway feasible.

Good Luck!