Configuring Multiple Subnets in One VLAN with DHCP on Cisco Router

ciscodhcpsubnetvlan

This is the scenario, a Cisco router with 1 VLAN with 2 or more subnets and a DHCP server inside of one of those subnets.

interface Vlan1
 ip address 192.168.0.1 255.255.255.0
 ip address 192.168.1.1 255.255.255.0 secondary
 ip address 192.168.2.1 255.255.255.0 secondary
 ...

Let's say the DHCP server is inside the subnet 192.168.0.1/24.

Will the DHCP server be able to broadcast to all clients inside all the subnets?

Will clients be able to do UDP broadcasts to all the subnets?

Will clients be able to communicate with clients in another subnet without problems?

Cheers!

Best Answer

From the DHCP server's point of view it's no different than any other VLAN and will respond accordingly. Keep in mind that - without additional information - the server has no idea to which secondary subnet a given client should belong.

UDP broadcasts map to an L2 broadcast address and so, yes, all clients on the subnet will receive the frame. That said, though, the broadcast will be ignored by the IP stacks of the clients not in the same subnet.

Clients will be able to communicate with one another, assuming they've been configured with the corresponding default gateway.

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