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Urgent Help: RAS's IP

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5 replies

by teinfo

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Tried to make a IP pool for RAS VPN connections. I like to setup 50 VPN client connection starting IP from x.x.x.100(Class C).

I entered IP address as: X.X.X.100
Mas as: X.X.X.192
This is class C.
Then RAS server came up IP Range as: x.x.x.102 To x.x.x.126
Number of address for clients is 63.

Problem: If I user 126-102=24 clients.

Does anyone knows how the RAS calculate the number of IP clients with 63?
Any Expert help me to enter a right Mask for IP x.x.x.100(Nedds 50 clients)
Thank in advance

5 replies

by stillatit

The mask is a 32 bit number (4 octets), which defines which bits of the IP address are "network" bits, and which are "nodes" (station addresses) on that network.

In theory, the number of nodes on a network should be a power of two, however the first address of a subnet is reserved for the subnet address, and the last address on the subnet is reserved for a broadcast address, so these two cannot be used for nodes.

Node Bits Mask Value Number of Nodes

2 2522
3 248 6
4 240 14
5 224 30
6 192 62

RAS may allow use of one of the two reserved addresses, giving you 63.

Mask x.x.x.192 will give you 62 clients per subnet, with the subnets starting at addresses x.x.x.1, x.x.x.65, x.x.x.129, x.x.x.193, BUT note that if you are subnetting a class C range, officially the first and last subnets ALSO cannot be used. (Whether it works or not depends on your routers.) This means that subnetting in this fashion will lose you 1/2 of your addresses.

You might want to think about having the RAS hand out 192.168.x.y addresses, and use NAT to let these users get to the internet if you need to.

Good luck.

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