I have had trouble searching for help on this one, as most searches for VLSM, CIDR and layer 3 switching bring back very basic questions posted by students just starting their CCNA.
I have a batch of public IPs that have been assigned to me. These come in on the end of an Ethernet cable out of the ISP's router. To keep things simple let's say that my ISP has given me a full 126.96.36.199/24 (hypothetical address). I would like to split that up into multiple distinct /28 networks. I have a layer 3 switch. Here's what I have tried:
I created three vlans on the switch. I created three interfaces and assigned each interface an IP address within the network range I desire. i.e:
- port1, vlan1 - 188.8.131.52/30
- port2, vlan2 - 184.108.40.206/29
port3, vlan3 - 220.127.116.11/29
The switch's default route is set to the ISP's router: 18.104.22.168
- Port 1 on the switch is connected to the ISP's router.
- Port 2 is connected to a computer with the address 22.214.171.124/29
- Port 3 is connected to a computer with the address 126.96.36.199/29
I have configured ip forwarding & routing and one computer can see the other using the switch as the default gateway. However, the computers can't ping the ISP's router and therefore are unable to communicate further up the network. If I use the switch's built-in ping command it is able to ping the ISP's router successfully and both computers. Is this because the ISP's router is configured as supplying 188.8.131.52/24 and therefore can't communicate properly with 184.108.40.206/30? I don't understand why the switch can ping the router but the clients can't even though they are using and going through the core switch.
I tried defining vlan1's interface address as 220.127.116.11/24 but then I was unable to configure the smaller /29 networks as I was told it overlapped with vlan1.
Appreciate any help one of the networking gurus can offer.