Different IP's on same Network

[sbruce66]

Hello All,

I have a client who we just found out is running 192.168.1.x and 10.10.10.1 on the same switches, we have never seen anything done like this before.Has anybody else ever seen this and can it be done without impact to the nextwork. They also have 2 gateways outside of their network handling different default gateways. The client say's it's working. However in my 10 years of networking I have never seen this done.

Scott

 

[ADB100]

Secondary addressing springs to mind as this is exactly what it is used for. From a layer-2 perspective the switches won't care about the layer-3 addressing, it is only the routers (or layer-3 switches) that get involved in IP forwarding anyway. There is also the possibility of proxy-arp being enabled that also allows stuff to work that you think really shouldn't.
Your comment about 'gateways outside their network' is a bit vague but it is possible they have two Internet connections (or just private WAN routers?) and each IP range uses different exit points from the network.

HTH

Andy

 

[sbruce66]

You are correct, they have 2 linksys gateways with seperate T1's. The voip phone has the 10.10.x.x address and the PC has 192.168.1.x address. Both IP addresses run off of a Netgear Router we plan to migrate them to CISCO soon. Not sure it would be a good idea to continue with the way they have things setup. What are your thought's?

Scott

 

[ADB100]

Sounds like a bodge job to be honest. Do the VoIP phones support Voice VLANs, if so that's the route I would go. With two IP networks on the same broadcast domain you are asking for trouble in my opinion - DHCP might be hit and miss if there are DHCP servers for both networks, connectivity between the two networks? how is that achieved etc.

You really need to draw up your game plan with all your objectives etc, then work out a suitable design.

HTH

Andy