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New Member

VLAN Bridging configuraiton on a 6509 (Sup720) with IOS 12.2(14)SX1

I am installing a 6509 (sup 720) to replace a multi-vlan network running on a 4006. The two networks will interconnect during migration. Users on OLD VLAN1 are being moved to various VLANs on new. Servers are also on VLAN1. This OLD VLAN1 is a /19 subnet and but the servers are alrady grouped into a /24 subnet. I want to move the server VLAN from the VLAN1(default) to VLAN10. We can not change server network addresses.

My plan was to create a VLAN10 on the 6509 with the same network as VLAN1 - BUT _ with a /24 mask and no routing entry. I thought that I could bridge between VLAN1 and VLAN10. When all the servers have been moved to the new server switches (3750s), and all users have moved to otehr VLANs, VLAN1 can be disabled and the routing entry be placed on VLAN10.

This would free up many subnets from the original address space.

Can this be done?

I have not been able to get bridging working between two defined VLANs. Each VLAN was given the same bridge group address. Bridging was enabled. Only one VLAN had a routing entry. Worktstations on both VLANs were given addresses in same subnet. But I was not able to ping.

If bridging will not work, any ideas on other approaches to get off VLAN1 and regain subnets?

  • Other Network Infrastructure Subjects
New Member

Re: VLAN Bridging configuraiton on a 6509 (Sup720) with IOS 12.2

What you're trying now certainly won't work.

The Cat6K sees the VLAN interfaces as routed layer 3 IP interfaces, and as such it will route and not bridge IP between them.

For your bridging scenario to work you'd have to use Integrated Routing and Bridging (IRB), but that's not supported on the Cat6K. states:

"Integrated routing and bridging (IRB) and concurrent routing and bridging (CRB) have deliberately been disabled on the Catalyst 6500 series switches and Cisco 7600 Series Internet Routers. You should use routable Layer 2 VLANs and VLAN interfaces for normal bridging and interVLAN routing. Bridge groups are supported only to bridge nonrouted protocols."

New Member

Re: VLAN Bridging configuraiton on a 6509 (Sup720) with IOS 12.2

Thank you for the clarrification. So my plan will not work.

Are there any suggestions on:

1. How to shrink the the subnet mask from /19 to /24 for the subnet being moved from the old network to the new? These are the servers so I can do not want to change their network.

2. Moving a network on VLAN1 to another VLAN (VLAN10) using same network number when migrating from old network to new?

Or am I stuck using VLAN1 with a /19 subnet on the new network?

New Member

Re: VLAN Bridging configuraiton on a 6509 (Sup720) with IOS 12.2

You don't want to do this with bridging. Make sure both the /19 and /24 are in the routing tables of both routers, then enable proxy arp (ala the interface configuration command ip proxy-arp) on all the router interfaces to VLAN 1. If you do this, everything in the /24 range will need to be located in VLAN 10.

It is not very elegant but has worked many times for me in the past.

hope this makes sense