ZyXEL MI-7248 User Guide - Page 281
Subnetting
View all ZyXEL MI-7248 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 281 highlights
Appendix A IP Addresses and Subnetting Subnet masks are expressed in dotted decimal notation just like IP addresses. The "natural" masks for class A, B and C IP addresses are as follows. Table 117 "Natural" Masks CLASS NATURAL MASK A 255.0.0.0 B 255.255.0.0 C 255.255.255.0 Subnetting With subnetting, the class arrangement of an IP address is ignored. For example, a class C address no longer has to have 24 bits of network number and 8 bits of host ID. With subnetting, some of the host ID bits are converted into network number bits. By convention, subnet masks always consist of a continuous sequence of ones beginning from the leftmost bit of the mask, followed by a continuous sequence of zeros, for a total number of 32 bits. Since the mask is always a continuous number of ones beginning from the left, followed by a continuous number of zeros for the remainder of the 32 bit mask, you can simply specify the number of ones instead of writing the value of each octet. This is usually specified by writing a "/" followed by the number of bits in the mask after the address. For example, 192.1.1.0 /25 is equivalent to saying 192.1.1.0 with mask 255.255.255.128. The following table shows all possible subnet masks for a class "C" address using both notations. Table 118 Alternative Subnet Mask Notation SUBNET MASK SUBNET MASK "1" BITS LAST OCTET BIT VALUE DECIMAL 255.255.255.0 /24 0000 0000 0 255.255.255.128 /25 1000 0000 128 255.255.255.192 /26 1100 0000 192 255.255.255.224 /27 1110 0000 224 255.255.255.240 /28 1111 0000 240 255.255.255.248 /29 1111 1000 248 255.255.255.252 /30 1111 1100 252 The first mask shown is the class "C" natural mask. Normally if no mask is specified it is understood that the natural mask is being used. MS-7206 User's Guide 281