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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 ...
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 ...
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.
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 router serves as a logical or physical boundary ...
2. Subnet mask (The /12 in the IP address in this case means only the left-most 12 bits are 1s, as shown here. This reserves the left 12 bits for the network address (prefix) and the right 32 - 12 = 20 bits for the host address (suffix).) 11111111.11110000.00000000.00000000: 255.240.0.0 3. Bit complement (bitwise NOT) of the subnet mask
Subnet mask: 4 octets: Client's subnet mask as per RFC 950. If both the subnet mask and the router option (option 3) are included, the subnet mask option must be first. 2: Time offset: 4 octets: Offset of the client's subnet in seconds from Coordinated Universal Time (UTC). The offset is expressed as a two's complement 32-bit integer.
When multiple route table entries match, the entry with the longest subnet mask is chosen as it is the most specific one. [2] If there are multiple routes with the same subnet mask, the route with the lowest metric is used. If there are multiple default routes, the metric is also used to determine which to use.
"More specific" means that it has a longer prefix. A /28 route, with a subnet mask of 255.255.255.240, is more specific than a /24 route, with a subnet mask of 255.255.255.0. If the route is of equal specificity to a route already in the routing table, but comes from a more preferred source of routing information, replace the route in the table.