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A wildcard mask can be thought of as an inverted subnet mask. For example, a subnet mask of 255.255.255.0 (11111111.11111111.11111111.00000000 2) inverts to a wildcard mask of 0.0.0.255 (00000000.00000000.00000000.11111111 2). A wild card mask is a matching rule. [2] The rule for a wildcard mask is: 0 means that the equivalent bit must match
Subnet masks are also expressed in dot-decimal notation like an IP address. For example, the prefix 198.51.100.0 / 24 would have the subnet mask 255.255.255.0 . Traffic is exchanged between subnets through routers when the routing prefixes of the source address and the destination address differ.
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 ...
Masks for IP ACLs are the reverse: for example, mask 0.0.0.255. This is sometimes called an inverse mask or a wildcard mask . When the value of the mask is broken down into binary (0s and 1s), the results determine which address bits are to be considered in processing the traffic.
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.
RFC 1918 name IP address range Number of addresses Largest CIDR block (subnet mask) Host ID size Mask bits Classful description [Note 1]; 24-bit block: 10.0.0.0 – 10.255.255.255: 16 777 216
As shown in the example below, in order to calculate the directed broadcast address to transmit a packet to an entire IPv4 subnet using the private IP address space 172.16.0.0 / 12, which has the subnet mask 255.240.0.0, the broadcast address is calculated as 172.16.0.0 bitwise ORed with 0.15.255.255 = 172.31.255.255. Directed broadcasts always ...
In this case, the longest prefix of the candidate routes is 192.168.20.16/28, since its subnet mask (/28) is longer than the other entry's mask (/16), making the route more specific. Forwarding tables often contain a default route , which has the shortest possible prefix match, to fall back on in case matches with all other entries fail.