Joining two subnets

[jason.williams]

I have a question regarding combining two subnets. I have a Cisco 3640 which I want to set the IP address to 223.253.253.253 255.255.255.252. I want this to be able to communicate with my LAN on a 10.1.0.0 255.255.0.0. The 3640 has only one network interface in it. If I put the primaryt address of the network interface to the IP above It does not see the network. What am I missing here?

[michael-faust]

I don't have a clear picture of your topology or your goals. You say that your router only has one interface. Do you mean only one LAN interface? Or does it have one LAN and one WAN interface? Are you trying to connect two local LAN segments or are the segments geographically separate? Tell us your overall goals and more details about your topology.

As far as your addressing goes there are two issues. First, a router should have an address on its interface that matches the network. In other words; if you put the address 223.253.253.253/30 on the router interface, it will expect that the 223.253.253.252/30 network is out that interface. Is it?

Second, where did you get that address and mask? With that address and mask the subnet broadcast address and the major network broadcast address are the same. Pick another address/mask.

Tell me more about your topology and I can help more. It's hard to give advice when I don't know your goals and limitations.

[nchidamb]

You can configure two sub-interfaces under the main interface and configure ip address to each of one of those sub-interfaces ( one belong to 223 subnet and other belongs to 10 network).

(or)

You can use "secondary address" to configure the same as well.

3640(config)#int e1/3

3640(config-if)#ip addr 10.1.0.1 255.255.0.0

3640(config-if)#ip addr 200.0.0.1 255.255.255.0 se

3640(config-if)#ip addr 200.0.0.1 255.255.255.0 secondary

This way, the router can communicate with both networks and route them accordingly.