DMVPN Hub IP Address Change

Answered Question
Mar 18th, 2010

Hello all!


I'm upgrading our network envirnment in the next few months to include a redudant Internet connection.  This change is requireing that our ISP switch us from a /30 to a /29.  Currently the 3845 router I have in the /30 subnet is the DMVPN hub for our 8 remote teleworkers that have 881 routers in their home offices.


The prepare for this IP address change, my thoughts were to create a new GRE tunnel interface with the new DMVPN hub settings before the IP address change takes place. Once we switch to the /29, the spoke routers should be able to reconnect to our network under the new tunnel interface.  We are running EIGRP over our DMVPN, so all routes should change to the new tunnel interface ones the tunnels is up.


Is this the best way to handle this?


Thanks for any feedback!

Correct Answer by trippi about 6 years 11 months ago

I don't think there is a better way to handle it than what you plan to do.

Create the new Tunnel with the new IP, once it is able to reach is it will come up automatically and route over that tunnel.


Or ask your ISP to let you hold onto the old /30 space for a week in order to do a graceful migration

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trippi Thu, 03/18/2010 - 13:50

Are you going to be keeping the same current IP addresses?

They are just resubnetting you and giving you more IPs?


If that is the case you could just change the gateway and subnet on your router and not have to create a new GRE tunnel interface...

Sam Oesterling Thu, 03/18/2010 - 13:56

They are resubnetting because they are going to configure HSRP on their end, so it is completely changing.  I also realized I will have to  change the GRE tunnel subnet since the routers won't let me overlap the IP address on the tunnel interfaces.


I have 8 routers all in different locations that are connecting to the hub.  I guess I could just make some minor modifications to the current tunnels , but I would have to walk non-techinical people to do that over the phone.  That would create more down time for the users, so I am trying to do more work behind the scenes.

Correct Answer
trippi Thu, 03/18/2010 - 14:03

I don't think there is a better way to handle it than what you plan to do.

Create the new Tunnel with the new IP, once it is able to reach is it will come up automatically and route over that tunnel.


Or ask your ISP to let you hold onto the old /30 space for a week in order to do a graceful migration

Sam Oesterling Fri, 03/19/2010 - 06:00

Asking the ISP to hold the /30 is a good idea.  I think I will do that.


Yeah I agree.  I think my way is the best way, but I just wanted to be 100% sure in case I overlooked something.  Thanks for your input!

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