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New Member

EIGRP

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?

 

 

 

1 ACCEPTED SOLUTION

Accepted Solutions

Is the interface you are

Is the interface you are changing the one connecting to the rest of the network?

just making sure the ip and mask will match the device on the other end.

24 REPLIES

Just to be clear you are

Just to be clear you are redistributing static routes with eigrp?

Do you have a network statement for your proposed change?

New Member

Yes Chris, you are right and

 

 

Is the interface you are

Is the interface you are changing the one connecting to the rest of the network?

just making sure the ip and mask will match the device on the other end.

New Member

yes. it is....in fact , i do

yes. it is....

in fact , i do this just to bring them all along within the network including other ends.

I don't see why it would

I don't see why it would affect the static routes.  As long as eigrp stays up it should redistribute the routes. 

New Member

i totally agree but

i totally agree but apparently earlier they attempted to change it with no success but i have no clue about  what happened nor the path the took &...so that is why i am trying to be proactive just in case...

In that case the subnet mask

In that case the subnet mask will have to match I believe for eigrp to work.

 

New Member

well... it is working just

well... it is working just the way it is now... but i dont know what to expect upon changing the mask and the interface... even though the network statement is gona stay the same but my concern are the static routes...

New Member

Chris...given that a few of

Chris...given that a few of our subnet mask are not matching with the eigrp s/ mask, what would be the solution? How can i make it work? we have a few vlans and they are running on a different subnet mask, so what do you suggest?

 

Depending on your design you

Depending on your design you could add the subnets to the EIGRP configuration if you are planning on using EIGRP for the routing protocol on those subnets.

for instance if one of the networks that isn't matching the eigrp mask is:

192.168.1.0 /24

you could add

router eigrp 2

network 192.168.1.0

it's kind of hard to tell given the information,

 

did you try making the subnet mask change, and it didn't redistribute the static routes?

 

New Member

Yes i did and they didn't get

Yes i did and they didn't get reditributed, it seems i have to add all those subnets (Network Statements) on both swicthes....(Primary too)

ok so on router Ayou have

ok so on router A

you have static routes

and eigrp configured

and router b has eigrp configured

but you don't see the static routes populating on router b?

i assume the mask for the 167.174.0.0 is /16

what is it changing to?
 

New Member

Basically....i have tested

Basically....i have tested both routers today (mock them on GNS3) and all is working great..static routes are populated and eigrp does its work...now i know the new subnet id and mask works and there is no issue whatsoever on the routers and they are not complaining about any subnet but upon connecting them to our switches they start complaining about two VLANs or IP address that they are on a different subnet and therefore eigrp neighborship never established.

We have three switches and they are all connected to VSS... so now i need to dig through all the configuration per switch to figure it out the possible bad configuration...

Any suggestion?

 

when you say the switches are

when you say the switches are complaining, is there an error popping up?

if so what's the error?

 

New Member

Yes, it says " EIGRP-IPv4 <1>

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...!

 

 

are the switches on different

are the switches on different subnets?

are you using the switches as layer3 switches?

 

 

New Member

Yes and yes.

Yes and yes.

so that's your problem,i don

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

New Member

it is pretty much yes...and

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...

 

Static routes? 

Static routes?

 

New Member

well... thank you....i have

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...!

what about this, can you

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.

New Member

Hey Chris,Thank you, this is

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...

 

 

 

Yeah i was just throwing that

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

Good Luck!

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