CIDR Block, Sonicwall, use ISP routed IP’s, many to one

docbob asked 2 years ago

Anybody have experience with CIDR IP blocks (SUBNETS)?? I saw an old post by AboveTheLogic user but the thread is now closed. I have a SonicWall router with 5 assigned IP's from the ISP (8 IP's, 5 usable, 248 subnet). I also have a B class range, 255.255.255.0 subnet, 255 ip's (owned by me) routed by the ISP to the first IP in the 248 subnet (CIDR I think). How do I capture and use these extra IP's?? Thanks in advance!!

1 Answers
Steve Bonilla Staff answered 2 years ago

There are a couple of ways to handle it.

1) Are you going to NAT requests to your CIDR block of IPs over to local IPs on your local private (RFC1918) network?

or

2) Do you need to create another network wherein hosts will be able to directly use the CIDR block of IP addresses?

For 1, just create NAT rules. Source "any", destination is the IP from the CIDR range you want, translated destination is the local IP. Make sure you have a counterpart firewall rule. I think you could use the Public Server Wizard for this. On the last step of the wizard, enter in the IP from your CIDR block in place of the WAN IP that the wizard places in there for you.

For 2, create another zone and call it something smart like "CIDR" block. Use an available SonicWALL interface (X4 for example), or create a virtual interface (using VLAN trunking, if you're out of interfaces), and assign it one of the IPs in the CIDR range. Create a routing rule that allows traffic destined to your CIDR block to route through (this rule might be auto-created). Then create a firewall rule that allows any traffic from any source to the CIDR block subnet.

The ISP will do just what you said, send any traffic destined for the CIDR subnet over to one of the IPs on your WAN interface. You need to tell the router how to handle those requests and where to send them, either through NAT or to the network itself which you must create.

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