assign the same ip address to two different vlans on two different switches


I have two x250e-48p switches in bldg A using vlan Alpha and one in bldg B using vlan Beta.

The two in bldg A (sw1A & sw2A ) are not stacked but connected by a cat5 cable connecting ports 48 on each. The vlan Alpha is the same but each switch has it's own vlan ip address.(1.1.1.1/24 & 1.1.2.1/24) respectfully.

When sw1A failed we moved the cable connecting bldg2 sw1B from sw1A port 47 to sw1B port 47,. Both ports are members of vlan Alpha and tagged for vlan Beta but machines in sw1B could not route to anything in the vlan Alpha.

I'm thinking I have a route issue that I cannot resolve. Perhaps a making the switches in BldgA is the best or only solution?

Can someone suggest a way to make physically moving the cable work?

8 replies

Userlevel 6
Hi Bud,

Based on what you put hear it appears there are more VLANs involved. The two IP addresses are in different VLANs. Unfortunately there is not enough information to provide you with an exact answer. Can you give us a topology, "show iproute" and some more VLAN information. We would need this information from all 3 switches to make an accurate recommendation.

Thanks!
Userlevel 4
Was the switch that failed also doing your routing?
yes, but there is only the two networks.
Userlevel 4
The two networks still need a router so one of your remaining switches will need to be configured as a router if you want to communicate between the two VLANs.
Userlevel 7
I agree with Curtis. You will likely need to enable ipforwarding, and possibly change the default gateway on the hosts.

-Brandon
I tried to keep it simple but that is proving not to be the best idea. Here is the topology. The switches are being used to provide voip connection for ip phones to an IP phone server in bldgA. Let me try again.....

Phone Server-------------------------sw1A 48--------------------------------48 sw1B

|

sw2A

sw1A & sw1B are in vlan Alpha while sw1B is in vlan Beta. Even though the vlans are named and tagged the same in both switch As they each have a different ip address. Ip forwording is enabled in all 3 switches and all vlans. The problem seems to be that the ip route in sw1B is sw1A's vlan Alpha address which ceases to exist when sw1a is removed by moving cables.

Phone Server sw1A 48 sw1B

| |

--------------------------------sw2A 50-----------------------------------
Userlevel 4
The switch designated as the router has to be in both VLANs, have IP addresses for both VLANs and (given your diagram) should be the only switch that has ip forwarding enabled. Is the configuration of the failed switch available where you can post it?
I think "flow redirect " may work. I will try it and let you know.

Reply