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In this address, 29 bits of the address are used to specify the network. The three
remaining bits are used to specify eight addresses on the subnet. With three bits used
to specify hosts on a 29-bit subnet, eight different bit combinations are possible. Of
those eight possible host addresses, two are reserved:
000 — Reserved for the network (base address)
001
010
100
110
101
011
111 — Reserved for the broadcast address of the subnet
Note
Early implementations of TCP/IP did not allow zero subnets (subnets with the
same base address as a class A, B, or C network). For example, the subnet
192.32.8.0/30 was illegal because it had the same base address as the class C network
192.32.8.0/24, while the subnet 192.32.8.4/30 was legal. Modern implementations
of TCP/IP support zero subnets, and the Stinger MRT implementation of RIP treats
these subnets the same as any other network. Make sure that you treat zero subnets
consistently throughout your network. Otherwise, you can encounter routing
problems.
Table 6-2 shows subnet masks and prefix lengths for a class C network.
Table 6-2. Decimal subnet masks and prefix lengths
Subnet mask
255.255.255.0
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
255.255.255.254
255.255.255.255
Stinger® MRT Getting Started Guide
Configuring Administrative Access, System Timing, and Startup Settings
Number of host addresses
254 hosts + 1 broadcast address, 1 network base
address
126 hosts + 1 broadcast address, 1 network base
address
62 hosts + 1 broadcast address, 1 network base
address
30 hosts + 1 broadcast address, 1 network base
address
14 hosts + 1 broadcast address, 1 network base
address
6 hosts + 1 broadcast address, 1 network base
address
2 hosts + 1 broadcast address, 1 network base
address
Invalid mask (no hosts)
1 host—a host route
Providing a basic system IP configuration
Prefix
length
/24
/25
/26
/27
/28
/29
/30
/31
/32
6-7
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