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

  • 0
  • 1
  • Question
  • Updated 3 years ago
  • Answered

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?

Photo of Morgan (Bud) Rosser

Morgan (Bud) Rosser

  • 100 Points 100 badge 2x thumb

Posted 3 years ago

  • 0
  • 1
Photo of Patrick Voss

Patrick Voss, Alum

  • 11,714 Points 10k badge 2x thumb
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!
Photo of Curtis Parish

Curtis Parish

  • 3,332 Points 3k badge 2x thumb
Was the switch that failed also doing your routing? 
Photo of Morgan (Bud) Rosser

Morgan (Bud) Rosser

  • 100 Points 100 badge 2x thumb

yes, but there is only the two networks.

Photo of Curtis Parish

Curtis Parish

  • 3,332 Points 3k badge 2x thumb
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.
Photo of Brandon Clay

Brandon Clay, Escalation Support Engineer

  • 13,608 Points 10k badge 2x thumb
I agree with Curtis. You will likely need to enable ipforwarding, and possibly change the default gateway on the hosts.


-Brandon
Photo of Morgan (Bud) Rosser

Morgan (Bud) Rosser

  • 100 Points 100 badge 2x thumb

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-----------------------------------

Photo of Curtis Parish

Curtis Parish

  • 3,332 Points 3k badge 2x thumb
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?  
Photo of Morgan (Bud) Rosser

Morgan (Bud) Rosser

  • 100 Points 100 badge 2x thumb
I think "flow redirect " may work. I will try it and let you know.