Why not use the network and netmask that the ISP gave you?
Hint: they are using the 3 high bits of the host octet to
subnet the Class C.
Class C: 207.234.111.0
11001111.11101010.01101111.00000000
Subnet: 207.234.111.64
11001111.11101010.01101111.01000000
^^^
The 010 indicated in the subnet address is part of a host
address in a Class C but part of the network address in
the subnet.
The Class C's netmask is 255.255.255.0, or
11111111.11111111.11111111.00000000
but for the gateway router also needs to mask off those extra 3 bits to
get the network number for your subnet from the 32-bit ipv4 address, so
the netmask for your subnet is 255.255.255.224, or
11111111.11111111.11111111.11100000
What the ISP sent you are the correct network and netmask numbers
for your network configuration scripts on your linux box to access
the ISP through the gateway host.
The range of assignable host ips in your subnet is
207.234.111.65 - 207.234.111.94.
The ISP's gateway used the first one, 207.234.111.65, and they assigned
you the second one, 207.234.111.66.
The lowest host ip in the subnet, last 5 bits all 0, is reserved for the
network number for the subnet, 207.234.111.64, and the highest host ip,
last 5 bits all 1, is the broadcast address for your subnet:
207.234.111.95
(So you don't want to use a whole Class C network number, netmask, and
broadcast address in your linux network config scripts for the interface
that connects to the ISP when the ISP actually assigns you a Class C
subnet network number and netmask. Everyone on the other subnets doesn't
want to get your broadcast packets and vice versa.)
There is a fine description of all of this in .pdf at
<http://www.3com.com/nsc/501302s.html>
Regards,
Clayton Weaver
<mailto:cgweav@eskimo.com>
(Seattle)
"Everybody's ignorant, just in different subjects." Will Rogers
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