User`s guide

IP Address Allocation

5-4

8000-A2-GB21-10

June 1997

To understand why this subnetting scheme works, you may want to consider the

IP addresses and subnet masks in hexadecimal:

Dotted Decimal

Dotted Hexadecimal

200.200.200.00 / 255.255.255.0 C8.C8.C8.00 / FF.FF.FF.00

200.200.200.240 / 255.255.255.240 C8.C8.C8.F0 / FF.FF.FF.F0

200.200.200.224 / 255.255.255.240 C8.C8.C8.E0 / FF.FF.FF.F0

200.200.200.208 / 255.255.255.240 C8.C8.C8.D0 / FF.FF.FF.F0

200.200.200.192 / 255.255.255.240 C8.C8.C8.C0 / FF.FF.FF.F0

In this illustration:

 Each of the four DSL ports is on a different subnetwork and the subnet mask

for the four ports is 255.255.255.240.

 The LAN port (10BaseT port) IP address is 200.200.200.

(where

can be

any valid IP address, but cannot be an IP address within the other subnets)

and its subnet mask is 255.255.255.0.

The illustration on page 5-5 shows an example of overall structured subnetting.

In this illustration, 16 ISPs are connected to one DSL card. The ISP router is

multihomed to support all 16 ISPs. Also, each RTU has 32 end-user systems

(ES).

In summary, if 32 end-user systems are connected to the DSL card’s port 1 and

all are using host addressing, then 32 host routes must be configured on the

RTU. If they are using structured subnet addressing, then only one route is

configured on the RTU.