Class C Subnetting Options for RAS Routing (139983)

SUMMARY

Windows NT Remote Access Service (RAS) routing for LAN connectivity to an Internet Provider requires an IP subnet address for the local LAN and a different subnet addresses for the RAS link.

This article describes subnetting options with a class C address. A class "C" address must be registered with the InterNIC. The InterNIC can be found at http://rs.internic.net or by sending mail to Hostmaster@NIC.DDN.MIL . Your Internet Service Provider may also supply you with a valid range of addresses.

MORE INFORMATION

Following are 3 options to configure different subnet addresses for the RAS link and local LAN:

Option 1

Have the Internet Provider give you one address to use on your RAS link outside of your class C addresses. This leaves you with the full 254 addresses for your own use and no special subnetting. Many Internet Providers will not give you an additional IP address. They may give you an entire additional class C range for a fee.

Option 2

Subnet mask of 255.255.255.192

This gives you 2 valid subnets with a maximum of 62 clients on the local LAN. Subnet 1 would have the fourth octet of 64-127 (65-126 can be assigned). Subnet 2 would have the fourth octet of 128-191 (129-190 can be assigned). For example XXX.XXX.XXX.65 would be the first address of subnet 1 and could be used for the Windows NT network card and XXX.XXX.XXX.129 would be the first address of subnet 2 and could be used for the RAS connection.

Option 3 (unsupported)

Subnet mask of 255.255.255.128.

This gives you 2 subnets with a maximum of 126 clients on the Local LAN. Both subnets are technically invalid but work with Windows NT 3.5 and 3.51. Be sure all clients on the network support this subnet mask. Microsoft cannot guarantee this will work in future releases of Windows NT. Subnet 1 would have the fourth octet of 0-127 (1-126 can be assigned). Subnet 2 would have the fourth octet of 128-255 (129-254 can be assigned). For example XXX.XXX.XXX.1 is the first address of subnet 1 and could be used for the Windows NT network card and XXX.XXX.XXX.129 is the first address of subnet 2 and could be used for the RAS connection.