This would allow it to talk to the second subnet on that VLAN but the only way it'll be able to talk to anything else is if there's a router/firewall running proxy arp that can help it out. This will cause the host to ARP for everything on or off it's subnet. In the gateway case if the host IP was 10.1.1.2 then the gateway would also be 10.1.1.2.

The only reason I can think of to do it is company mergers or network upgrades and for both of those I'd prefer it to be temporary.Įdit to clarify, for the hosts on different subnets but the same VLAN to talk directly you'd need to either make them their own default gateway or add a route to the 'other' subnet that connects it to the interface. One VLAN = one subnet is easier to document and easier to troubleshoot and there's usually not a good reason to complicate things. We generally don't do it because of the messiness and lack of security. It's messy from a documentation and troubleshooting perspective.Allows the subnets to talk directly without a router or firewall.There's really no reason not to put multiple subnets on the same VLAN, but there's also probably no reason to do it. I found this topic which seems similar, but the purpose is not the same. Now, nobody does that and I supposed it is for some goods reasons, but I did not find what are those reasons and that is what I am asking you ? Note : each side of the topology has a host from network A and B All ports of each switch are in access mode with vlan 10 and 20 respectively. I also tried the same configuration but with a second switch and a different vlan number (SW1 with vlan 10 and SW2 with vlan 20). But I am confused since I can configure 2 working networks within the same LAN. The idea/principle of a LAN/vLAN is, in the course I've followed, described as a broadcast domain.

Host and network A cannot talk to host in network B which is normal since inter-LAN communications need a 元 device with routing function.

And host in network B (ex: 10.2.2.0/24) cant talk to each other.

Host in network A (ex: 10.1.1.0/24) can talk to each other.

I would like to know why we do not (and should not I guess) use 2 different networks on the same LAN/vLAN.

Beebeep multiple subnet