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A wildcard mask is a mask of bits that indicates which parts of an IP address are available for examination. In the Cisco IOS, [1] they are used in several places, for example: To indicate the size of a network or subnet for some routing protocols, such as OSPF. To indicate what IP addresses should be permitted or denied in access control lists ...
In the above example, the subnet mask consists of 26 bits, making it 255.255.255.192, leaving 6 bits for the host identifier. This allows for 62 host combinations (2 6 −2). In general, the number of available hosts on a subnet is 2 h −2, where h is the number of bits used for the host portion of the address.
Used for loopback addresses to the local host [1] 169.254.0.0/16 169.254.0.0–169.254.255.255 65 536: Subnet Used for link-local addresses [5] between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server 172.16.0.0/12 172.16.0.0–172.31.255.255 1 048 576: Private ...
A subnet mask is a bitmask that encodes the prefix length associated with an IPv4 address or network in quad-dotted notation: 32 bits, starting with a number of 1-bits equal to the prefix length, ending with 0-bits, and encoded in four-part dotted-decimal format: 255.255.255.0. A subnet mask encodes the same information as a prefix length but ...
A layer-3 segment in an IP network is called a subnetwork, formed by all nodes sharing the same network prefix as defined by their IP addresses and the network mask. [5] Communication between layer-3 subnets requires a router. Hosts on a subnet communicate directly using the layer-2 segment that connects them.
The network address and subnet mask of the interface, along with the interface type and number, are entered into the routing table as a directly connected network. A remote network is a network that can only be reached by sending the packet to another router.
The term subnet mask is only used within IPv4. Both IP versions however use the CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix. For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0, respectively.
The packet is then forwarded to the external network. The NAT device then makes an entry in a translation table containing the internal IP address, original source port, and the translated source port. Subsequent packets from the same internal source IP address and port number are translated to the same external source IP address and port number.