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New Member

Overlapping IP and/or subnet

Hi,

I have this weird scenario whereby my customer wanted 3 VLANs and each VLANs should have the same IP.

PC1 (192.168.1.2/24) in VLAN1.

PC2 (192.168.1.2/24) in VLAN2.

PC3 (192.168.1.2/24) in VLAN3.

Is that even possible?

5 REPLIES
Bronze

Overlapping IP and/or subnet

Hi,

Yes is it possible with using private vlan. Look link below.

http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.2/31sga/configuration/guide/pvlans.html

hth

Muammer

Overlapping IP and/or subnet

Not possible. Switch will throw you an error about overlapping IP subnets.

Thanks

Vivek

New Member

Overlapping IP and/or subnet

Hi all, I just got the full information on the setup that my customer wish to do. Basically this is a railway track. There are a total of 12 train stations here. So each train station will have a L2 switch.

Station 1 Switch 1 VLAN 1

Station 2 Switch 2 VLAN 2

     .

     .

     .

Station 12 Switch 12 VLAN 12

All these above L2 switches will be wired back to the core switch in a different location.

Now the customer is going to deploy camera (192.168.1.2/24) on all the train. So when the train reach every station, the camera can connect back to the camera server to provide the image feed without changing IP address. We can expect there will be more than 1 train (all of them with camera and IP of 192.168.1.2/24) stopping at different stations and want to communicate with the server.

Can we do this with PVLAN? Or can we do some form of NAT?

New Member

Overlapping IP and/or subnet

12 vlans --12 stations --12 trains, one stopped in each station, --12 camera one active in each station -all camera same IP

If your VLANs are all routed by the same router this is not possible.

Imagine that the router will have to send one packet back to 192.168.1.2. Which camera is going to receive the packet :-) ?

I am having trouble to figure out how the routing table or the arp table of such router will look like in order to meet the requirements.

You need different IP ranges or some NAT on an intermediate router

I am not familiar with bridging but that might solve the problem too but yu need a L2 protocol for  the camera

The idea behind private vlans is that in the end all the private vlans share a comon gateway. This solution (pvlans) is supposed to save IP addresses(you do not waste 2 IP pers subnet every time you subnet an IP range in order to separate customers).

Overlapping IP and/or subnet

Hi,

so there will be an L2 (hub and spokes) connection between all the stations and the central site?

Why don't you simply assign different IP addresses 192.168.1.1 ...192.168.1.12 to particular cameras?

Each camera would just connect to a new switch when arrived to a new station but would keep the same IP address all the time.

And from your network point of view you would just see the camera's MAC address moving from one switch to another.

As I suppose it takes some time to move the train from one station to another, you might even not see "MAC address flapping" error in the switch logs.

HTH,

Milan

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