Glossary
GL-18
Cisco Router and Security Device Manager Version 2.2 User’s Guide
OL-4015-08
logical interface An interface that has been created solely by configuration, and that is not a
physical interface on the router. Dialer interfaces and tunnel interfaces are
examples of logical interfaces.
loopback In a loopback test, signals are sent and then redirected back toward their source
from some point along the communications path. Loopback tests are often used
to determine network interface usability.
M
MAC message authentication code. The cryptographic checksum of the me ssage used
to verify message authenticity. See hash.
mask
subnet mask
netmask
network mask
A 32-bit bit mask which specifies how an Internet address is to be divided into
network, subnet, and host parts. The net mask has ones (1’s) in the bit positions
in the 32-bit address that are to be used for the network and subnet parts, and has
zeros (0’s) for the host part. The mask should contain at least the standard
network portion (as determined by the address class), and the subnet field should
be contiguous with the network portion. The mask is configured using the
decimal equivalent of the binary value.
Examples:
Decimal: 255.255.255.0
Binary: 11111111 11111111 11111111 00000000
The first 24 bits provide the network and subnetwork address, and the last 8
provide the host address.
Decimal: 255.255.255.248
Binary: 11111111 11111111 11111111 11111000
The first 29 bits provide the network and subnetwork address, and the last 3
provide the host address.
See also IP Address, TCP/IP, host, host/network.