I have a situation where I have ethernet traffic from two separate networks/ip subnets (Subnet A and Subnet B) on a single ethernet connection. I have the need to separate the traffic into two separate networks and two isolated broadcast domains. I thought this could easily be accomplished with a Cisco 300 Layer 3 switch, but I can't get it to work correctly.
I have the switch set to IP routing mode. I have three VLANs configured. VLAN 1 sees the combined Layer 2 & 3 ethernet traffic for both subnet A and subnet B. VLAN 10 has an IP address assigned from subnet A and is the gateway for devices within that subnet. VLAN 20 has an IP address assigned from subnet B and is the gateway for devices within that subnet. IP proxy arp is on by default and should be active.
Devices in VLAN 10 can ping devices in VLAN 20 and devices in VLAN 20 can ping devices in VLAN 10. This appears to be working only because the switch is the default gateway for those components.
No devices or servers in VLAN 1 can ping VLAN 10 or VLAN 20 components, and VLAN 10 and VLAN 20 components can not ping VLAN 1. I analyzed the ARP traffic on VLAN 1 and the switch is not responding with its own MAC address for requests for IPs for active devices connected to VLAN 10 or VLAN 20. The Cisco documentation says that the device should be responding and acting as a router.
I can not physically connect everthing on VLAN 1 directly to the switch, I can not make the switch the default gaeway for all devices on VLAN 1, and I can not create static routes directly to the VLAN 1 switch IP address for all devices that are part of VLAN 1, so I am stuck. I need the switch to let VLAN 1 components automatically know what is connected to VLAN 10 and VLAN 20.
I am willing to scrap this approach entirely if there is an easier way to do this. Put simply, I have a few devices in Subnet A that need to be isolated from Layer 2 & 3 traffic destined for a few devices in Subnet B, but I can't reconfigure my entire network to create these isolated broadcast domains.