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GB-Ware Firewall Product Guide28
Using CIDR-based or Slash (/) Notation
CIDR (Classless Inter-Domain Routing) aggregates routes so that one
IP address represents thousands served by a backbone provider. GNAT Box
System Software uses CIDR-based notation as the default for subnet masks,
instead of dotted decimal (e.g. 255.255.255.0) notation.
Instead of the fixed 8, 16 and 24 bits used in dotted decimal Class A, B, or C
net masks, CIDR-based notation can further divide the network into subnets
by using bit masking of any number from 1 to 32 to determine network
class (/32 representing one IP address). For example, the CIDR address
204.12.01.42/24 indicates that the first 24 bits are used for the network class
ID. The /24 mask includes 254 hosts on the network, and is equivalent to
255.255.255.0 in dotted-decimal notation.
Calculate a CIDR-based notation net mask by converting the dotted decimal
net mask to binary and count the ones. For a Class C network, the dotted
decimal net mask is 255.255.255.0. The binary notation of that net mask is
11111111.11111111.11111111.00000000. There are 24 ones, so the CIDR
notation would be /24. Using a 255.255.255.240 net mask, the binary repre-
sentation would be: 11111111.11111111.11111111.11110000. The notation
would be /28.
You may also enter a host address that is defined by not including a bit mask
(e.g. 192.168.123.1). This is equivalent to a /32 bit mask. To enter a range
of addresses, use a hyphen (-) between the two extremes of the range (e.g.
192.168.123.0-192.168.123.255).
Dotted decimal may still be used by entering the dotted decimal net mask
after the forward slash.
Re-configuring Your Computer
If you temporarily changed your computer’s network configuration to
connect to the firewall, restore the original configuration now. If you formed
a temporary peer network during network configuration, disassemble it
now; reconnect your computer and the firewall to your network. Now your
computer and firewall should both be members of your network. Reboot
your computer if necessary to affect the network configuration change.
Accessing the Firewall
Access the firewall using the IP address you assigned to the protected
network.
The firewall should now be active and functioning in default security mode
(all internal users are allowed outbound and no unsolicited inbound connec-
tions are allowed). You can now perform any additional configuration tasks,
including changing the administrative password.