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Glossary 155
Glossary
SRQ
Service Request. An asynchronous request (an interrupt) from a remote
device indicating that the device requires servicing.
subnet
A portion of a network that shares a common address component. On
TCP/IP networks, subnets are defined as all devices whose IP addresses
have the same prefix. For example, all devices with IP addresses that
start with 100.100.100. would be part of the same subnet. Dividing a
network into subnets is useful for both security and performance reasons.
IP networks are divided using a subnet mask.
subnet mask
A mask used to determine to what subnet an IP address belongs. An IP
address has two components: the network address and the host address.
For example, consider the IP address 150.215.017.009. Assuming this is
part of a Class B network, the first two numbers (150.215) represent the
Class B network address and the second two numbers (017.009) identify
a particular host on this network.
Subnetting enables a System Administrator to further divide the host part
of the address into two or more subnets. In this case, a part of the host
address is reserved to identify the particular subnet.
For example, the full address for 150.215.017.009 is
10010110.11010111.00010001.00001001. The Class B network part is
10010110.11010111 and the host address is 00010001.00001001. If this
network is divided into 14 subnets, the first four bits of the host address
(0001) are reserved for identifying the subnet.
The subnet mask is the network address plus the bits reserved for
identifying the subnetwork. (By convention, the bits for the network
address are all set to 1, though it would also work if the bits were set
exactly as in the network address.) In this case, the subnet mask is
11111111.11111111.11110000.00000000.
It is called a mask because it can be used to identify the subnet to which
an IP address belongs by performing a bitwise AND operation on the
mask and the IP address. The result is the subnetwork address:
Subnet Mask 255.255.240.000 11111111.11111111.11110000.00000000
IP Address 150.215.017.009 10010110.11010111.00010001.00001001
Subnet Address 150.215.016.000 10010110.11010111.00010000.00000000
The default subnet mask for the E5810 is 255.255.0.0