316 Chapter 5: Network Protocols
Table 5-37 summarizes NAT terminology.
Mask
A generic term for a mask, whether it is a default mask or a subnet
mask.
Address mask
Another term for a mask.
Default Class A mask
The mask used for Class A networks when no subnetting is used.
The value is 255.0.0.0.
Default Class B mask
The mask used for Class B networks when no subnetting is used.
The value is 255.255.0.0.
Default Class C mask
The mask used for Class C networks when no subnetting is used.
The value is 255.255.255.0.
Subnet mask
A nondefault mask used when subnetting.
Network part or network
field
Term used to describe the first part of an IP address. The host part is 8,
16, or 24 bits for Class A, B, and C networks, respectively.
Host part or host field
Term used to describe the last part of an IP address. The network part is
24, 16, or 8 bits for Class A, B, and C networks, respectively, when
subnetting is not used. When subnetting, the size of the host part
depends on the subnet mask chosen for that network.
Subnet part of subnet field
Term used to describe the middle part of an IP address. The subnet part
is variable in size, based on how subnetting is implemented.
Table 5-37
NAT Addressing Terms
Term
Meaning
Value in Figure
5-26
Inside local
Address of the host in the private network. When NAT is
needed, this address is typically a private address or an
address in a network registered to another organization.
170.1.1.10
Inside global
The Internet (global network) view of the inside local
address. This address is in a network registered to the
company responsible for the NAT router.
200.1.1.1
Outside global
The Internet (global network) view of the address of the
host correctly attached to the Internet.
170.1.1.1
Outside local
When the private company reuses a network number
registered to someone else, the outside local address
represents the outside global address in the local
(private) network. Because this address is used only in
the private organization, it can be any IP address.
192.168.1.1
Table 5-36
IP Addressing Terminology (Continued)
Term
Definition
ch05.fm Page 316 Monday, March 20, 2000 5:06 PM