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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 ...
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 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
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 network with the longest subnet mask or network prefix that matches the destination IP address is the next-hop network gateway. The process repeats until a packet is delivered to the destination host, or earlier along the route, when a router has no default route available and cannot route the packet otherwise.
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.
When an interface has an address configured in a subnet, such as 192.0.2.1 in the 192.0.2.0/24 (i.e., subnet mask 255.255.255.0) subnet, and that interface is considered "up" by the router, the router thus has a directly connected route to 192.0.2.0/24. If a routing protocol offered another router's route to that same subnet, the routing table ...