Netgear FVS318 FVS318v3 Reference Manual - Page 150

mask 255.255.255.0 into 16 subnets 4 bits, the new subnet mask becomes 255.255.255.240. - replacement

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Reference Manual for the ProSafe VPN Firewall FVS318v3 Although the preceding example uses the entire third octet for a subnet address, note that you are not restricted to octet boundaries in subnetting. To create more network numbers, you need only shift some bits from the host address to the network address. For instance, to partition a Class C network number (192.68.135.0) into two, you shift one bit from the host address to the network address. The new netmask (or subnet mask) is 255.255.255.128. The first subnet has network number 192.68.135.0 with hosts 192.68.135.1 to 129.68.135.126, and the second subnet has network number 192.68.135.128 with hosts 192.68.135.129 to 192.68.135.254. Note: The number 192.68.135.127 is not assigned because it is the broadcast address of the first subnet. The number 192.68.135.128 is not assigned because it is the network address of the second subnet. The following table lists the additional subnet mask bits in dotted-decimal notation. To use the table, write down the original class netmask and replace the 0 value octets with the dotted-decimal value of the additional subnet bits. For example, to partition your Class C network with subnet mask 255.255.255.0 into 16 subnets (4 bits), the new subnet mask becomes 255.255.255.240. Table B-1. Netmask notation translation table for one octet Number of Bits 1 2 3 4 5 6 7 8 Dotted-Decimal Value 128 192 224 240 248 252 254 255 The following table displays several common netmask values in both the dotted-decimal and the masklength formats. Table B-2. Netmask formats Dotted-Decimal 255.0.0.0 Masklength /8 B-6 Network, Routing, and Firewall Basics January 2005

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Reference Manual for the ProSafe VPN Firewall FVS318v3
B-6
Network, Routing, and Firewall Basics
January 2005
Although the preceding example uses the entire third octet for a subnet address, note that you are
not restricted to octet boundaries in subnetting. To create more network numbers, you need only
shift some bits from the host address to the network address. For instance, to partition a Class C
network number (192.68.135.0) into two, you shift one bit from the host address to the network
address. The new netmask (or subnet mask) is 255.255.255.128. The first subnet has network
number 192.68.135.0 with hosts 192.68.135.1 to 129.68.135.126, and the second subnet has
network number 192.68.135.128 with hosts 192.68.135.129 to 192.68.135.254.
The following table lists the additional subnet mask bits in dotted-decimal notation. To use the
table, write down the original class netmask and replace the 0 value octets with the dotted-decimal
value of the additional subnet bits. For example, to partition your Class C network with subnet
mask 255.255.255.0 into 16 subnets (4 bits), the new subnet mask becomes 255.255.255.240.
The following table displays several common netmask values in both the dotted-decimal and the
masklength formats.
Note:
The number 192.68.135.127 is not assigned because it is the broadcast address
of the first subnet. The number 192.68.135.128 is not assigned because it is the network
address of the second subnet.
Table B-1.
Netmask notation translation table for one octet
Number of Bits
Dotted-Decimal Value
1
128
2
192
3
224
4
240
5
248
6
252
7
254
8
255
Table B-2.
Netmask formats
Dotted-Decimal
Masklength
255.0.0.0
/8