subnet mask


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Related to subnet mask: IP address, Subnetting, Default gateway

subnet mask

subnet mask

(SUBNETwork mask) The technique used by the TCP/IP communications protocol that identifies which network segment a packet belongs to. The subnet mask is a binary pattern, and the default mask found in countless small local networks indicates that all the machines are in the same network (see below). See subnet, IP address and TCP/IP.

A Tradeoff Between Hosts and Subnets
The bits in the mask identify both hosts and subnets. The more hosts, the fewer subnets; the more subnets, the fewer hosts can be individually addressed. These bits become a tradeoff based on the network class (A, B or C).

Class C Subnet Mask Examples
Subnet masks for a Class C network (small network) use the first 24 bits for subnet ID and the last 8 for host ID. These last 8 are divided between hosts and subnets (for more on network classes, see subnet mask tables).

In Example #1 below, the 255.255.255 are the numeric values of three sets of eight 1 bits. The 0 means eight 0 bits. There are "no" subnets, and up to 254 hosts can be addressed in this network (255 minus 1).

Example #1Class C Default Mask (No Subnets)255.255.255.0
 11111111.11111111.11111111.00000000


 Example #2Class C Mask for Six Subnets255.255.255.224
 11111111.11111111.11111111.11100000
                            ssshhhhh

In Example #2 above, the 224 reserves the three high-order bits of that byte for subnets (sss), leaving the remaining five bits for hosts (hhhhh). The 224 creates six subnets from 001 to 110 (000 and 111 are reserved), and each subnet can have 30 hosts from 00001 to 11110. Likewise, 00000 and 11111 are reserved: 00000 means "this" node, and 11111 means "all" nodes (see broadcast address). This is why calculations for maximum hosts and subnets are always minus 2.
References in periodicals archive ?
In the architecture of DHCP, the DHCP server is responsible for maintaining the IP address pool and other network parameters, such as subnet mask and default DNS.
Firstly, comparing to RIP, OSPF is a classless protocol which allows utilization of different subnet masks, which essentially gives network administrators more flexibility with IP addresses and less wastage.
For the common Class C addresses, where the first three octets represent the network address and the last octet represents the host/node number on that network, the subnet mask would be 255.255.255.0.
Next we prepare the network devices, which need two pieces of information to communicate: an Internet protocol (IP) address on the network (four sets of numbers) and a subnet mask. Some network devices are configured automatically, but doing it manually is not difficult, although, as you'll see, it involves many steps.
He used the default IP address and password to change the configuration of the access point, and then he assigned a new IP address, subnet mask, and password and enabled the security protocols using the 1 28-bit WEP (Wireless Equivalent Privacy) security and a passphrase.
* The destination prefix (an IP address plus subnet mask; for instance 23.154.56.0/24, which represents 256 IP addresses).
The service includes a qualified member of Geac's Customer Response Center (CRC) configuring the library system's TCP/IP interface with the correct IP address, subnet mask, broadcast address, etc.; setting Hostname, Nodename, and Domain Name so that they match the names on the Internet registration form; configuring the route table entries so that the system has access beyond the local subnet for programs such as telnet and e-mail; installing the sendmail configuration; and creating a generic OPAC login to make the system accessible to patrons coming in from die Internet, leading users directly from die login prompt to the main OPAC menu.
The range 0-63 cannot be used with that subnet mask, since in that case the subnet field would consist of all zeroes.
To determine whether the destination device is on the local subnet or on a remote one, i.e., whether the message may be sent to the destination device directly or must be sent to the IP gateway, the originating device uses a configuration parameter called the "subnet mask," AND's it with the source and destination IP addresses, and compares the results.
In TCP/IP, a subnet mask separates the network ID from the host ID.
It also automatically configures itself, including selecting an appropriate IP address and subnet mask, which allows me to have a `virtual presence' anywhere on the network.