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vlan switching

I have two 2950 switches linked to a 4506 switch which is onward linked to a router. The two 2950s both support two seperate subnets.

I don't want to implement VLANs (for reasons I won't go into here) but I do want the switch to pass packets between the two across the backplane rather than handing them to the router.

I attempted to implement Layer 3 switching by first enabling it (ip routing command) and then giving the default VLAN interface a secondary IP address so that it was virtually linked to both subnets. This meant that both network entries existed in the routing table of the switch (I checked!).

Next, a static route was added to the PCs (yes - the PCs) in both subnets telling them to send all packets to the other subnet via the appropriate address on the switch VLAN interface. Their default gateway however remained as the router. The metric for the static route was 1.

So...

In theory, when the switch received traffic from one subnet destined for the other, it should have checked the IP address against it's routing table (both entries were there - I checked) and rerouted the packet to its destination.

However the switch continued to pass traffic to the router rather than layer 3 switching directly across the backplane. Any ideas why this didn't work, or is my theory just way out?

The commands issued to the 4506 were

ip routing enabled

interface vlan1

ip address x.x.x.x x.x.x.x secondary

Cheers

Duncan

  • LAN Switching and Routing
2 REPLIES

Re: vlan switching

Hi

Can u try giving the ip's of u r vlan 1 as the gateway for u r clients.

Thanks

Mahmood

Bronze

Re: vlan switching

A good question. I agree with mahmood that you should have the DefGW as the VLAN interface IP. Whenever the clients will send an ARP request, it will be received and processed by both the subnets. It should work then.

Let us know if it works.

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