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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 ...
Starting 1991-06-01, was used to map Public Data Network addresses to IP addresses. Returned to IANA 2008-01-22. This network was reclaimed by IANA in 2007 and was subsequently re-allocated in 2010. See RFC 877 and RFC 1356 for historical information. [10] 15.0.0.0/8 ARIN: 1991-09
A subnetwork, or subnet, is a logical subdivision of an IP network. [ 1 ] : 1, 16 The practice of dividing a network into two or more networks is called subnetting . Computers that belong to the same subnet are addressed with an identical group of its most-significant bits of their IP addresses .
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.
Both the IPv4 and the IPv6 specifications define private IP address ranges. [ 1 ] [ 2 ] Most Internet service providers (ISPs) allocate only a single publicly routable IPv4 address to each residential customer, but many homes have more than one computer , smartphone , or other Internet-connected device.
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 network Used for local communications within a private network [3] 192.0.0.0/24 192.0.0.0–192.0.0.255 256
Previously, every link needed to dedicate a / 31 or / 30 subnet using 2 or 4 IP addresses per point-to-point link. When a link is unnumbered, a router-id is used, a single IP address borrowed from a defined (normally a loopback) interface. The same router-id can be used on multiple interfaces.
A subnet mask encodes the same information as a prefix length but predates the advent of CIDR. In CIDR notation, the prefix bits are always contiguous. Subnet masks were allowed by RFC 950 [6] to specify non-contiguous bits until RFC 4632 [5]: Section 5.1 stated that the mask must be left contiguous. Given this constraint, a subnet mask and ...