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Moving a sites default gateway

Answered Question
Oct 26th, 2006
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Hi, Our sites current default gateway points to an old 3660 series router which serves little purpose any more, as a few years back our WAN was outsourced and we now have the suppliers routers on our site which advertise our networks to the 3660 using EIGRP. Other than that, there are a couple of static routes on the 3660 for legacy networks.

We upgraded our LAN last year, and now have two 4506 switches at the core, with HSRP configured.

We need to migrate the default gateway from the 3660 to the virtual address of the core switches (HSRP group address). I'd like to run through a few things with you kind people first though...


1) For testing purposes, if I enabled EIGRP on the core switches now, and repointed my default gateway to the HSRP address, would it cause any routing problems on our network (i.e. would it cause problems with the existing default gateway - obviously the HSRP address is different to our default gateway!). Or would the core simply learn the routes, but since no clients are set to use the core as a default gateway, there would be no changes to the topology of the current network?

2) Assuming the implementation of EIGRP went okay, I'd enter the static routes and then change the HSRP address to that of the sites default gateway, whilst also turning off the 3660 (current gateway). Is there anything else I'd need to do?


Thanks for your help in advance!

Hi, without seeing a diagram,routing tables and configs it's difficult to say for 100% but it sounds like you are going in the right direction. If I understand currently your hosts point to the legacy 3660 as their default gateway and you want them to use the 4506's for this. So enable EIGRP on the 4506 and confirm the adjacency is up and the required routes are available. You could then setup a test machine to point to the HSRP address of the 4506. If all routing works you could then change GW of other hosts. It sounds like this is pretty much what you have planned!

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Hi, without seeing a diagram,routing tables and configs it's difficult to say for 100% but it sounds like you are going in the right direction. If I understand currently your hosts point to the legacy 3660 as their default gateway and you want them to use the 4506's for this. So enable EIGRP on the 4506 and confirm the adjacency is up and the required routes are available. You could then setup a test machine to point to the HSRP address of the 4506. If all routing works you could then change GW of other hosts. It sounds like this is pretty much what you have planned!

tonymitchell Thu, 10/26/2006 - 03:41
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Hi Mark, Thanks for you reply. You are right in your understanding of what I'm trying to achieve and it sounds like you agree that I'm on the right track, so that's good to know! The only difference, is that I'm planning of changing the HSRP address to the 3660 address, rather than change the GW of all hosts.

My main worry, was enabling EIGRP on the core switches and causing wierd routing issues.

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