Wildcard mask

Last updated

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:

A wildcard mask can be thought of as an inverted subnet mask. For example, a subnet mask of 255.255.255.0 (11111111.11111111.11111111.000000002) inverts to a wildcard mask of 0.0.0.255 (00000000.00000000.00000000.111111112).

A wild card mask is a matching rule. [2] The rule for a wildcard mask is:

Any wildcard bit-pattern can be masked for examination. For example, a wildcard mask of 0.0.0.254 (00000000.00000000.00000000.111111102) applied to IP address 10.10.10.2 (00001010.00001010.00001010.000000102) will match even-numbered IP addresses 10.10.10.0, 10.10.10.2, 10.10.10.4, 10.10.10.6 etc. Same mask applied to 10.10.10.1 (00001010.00001010.00001010.000000012) will match odd-numbered IP addresses 10.10.10.1, 10.10.10.3, 10.10.10.5 etc.

A network and wildcard mask combination of 1.1.1.1 0.0.0.0 would match an interface configured exactly with 1.1.1.1 only, and nothing else.

Wildcard masks are used in situations where subnet masks may not apply. For example, when two affected hosts fall in different subnets, the use of a wildcard mask will group them together.

List of wildcard masks
SlashNetmaskWildcard mask
/32255.255.255.2550.0.0.0
/31255.255.255.2540.0.0.1
/30255.255.255.2520.0.0.3
/29255.255.255.2480.0.0.7
/28255.255.255.2400.0.0.15
/27255.255.255.2240.0.0.31
/26255.255.255.1920.0.0.63
/25255.255.255.1280.0.0.127
/24255.255.255.00.0.0.255
/23255.255.254.00.0.1.255
/22255.255.252.00.0.3.255
/21255.255.248.00.0.7.255
/20255.255.240.00.0.15.255
/19255.255.224.00.0.31.255
/18255.255.192.00.0.63.255
/17255.255.128.00.0.127.255
/16255.255.0.00.0.255.255
/15255.254.0.00.1.255.255
/14255.252.0.00.3.255.255
/13255.248.0.00.7.255.255
/12255.240.0.00.15.255.255
/11255.224.0.00.31.255.255
/10255.192.0.00.63.255.255
/9255.128.0.00.127.255.255
/8255.0.0.00.255.255.255
/7254.0.0.01.255.255.255
/6252.0.0.03.255.255.255
/5248.0.0.07.255.255.255
/4240.0.0.015.255.255.255
/3224.0.0.031.255.255.255
/2192.0.0.063.255.255.255
/1128.0.0.0127.255.255.255
/00.0.0.0255.255.255.255

Related Research Articles

Interior Gateway Routing Protocol (IGRP) is a distance vector interior gateway protocol (IGP) developed by Cisco. It is used by routers to exchange routing data within an autonomous system.

An Internet Protocol address is a numerical label such as 192.0.2.1 that is connected to a computer network that uses the Internet Protocol for communication. An IP address serves two main functions: network interface identification and location addressing.

The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when communicating with another IP address, for example, an error is indicated when a requested service is not available or that a host or router could not be reached. ICMP differs from transport protocols such as TCP and UDP in that it is not typically used to exchange data between systems, nor is it regularly employed by end-user network applications.

<span class="mw-page-title-main">Internet Protocol version 4</span> Fourth version of the Internet Protocol

Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version deployed for production on SATNET in 1982 and on the ARPANET in January 1983. It is still used to route most Internet traffic today, even with the ongoing deployment of Internet Protocol version 6 (IPv6), its successor.

Classless Inter-Domain Routing is a method for allocating IP addresses and for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet. Its goal was to slow the growth of routing tables on routers across the Internet, and to help slow the rapid exhaustion of IPv4 addresses.

Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous system (AS).

In computer networking, a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes. The routing table contains information about the topology of the network immediately around it.

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary protocol, available only on Cisco routers. In 2013 Cisco decided to allow other vendors freely implement limited version of EIGRP with some of its associated features such as High Availability (HA), while withholding other EIGRP features such as EIGRP stub, needed for DMVPN and large-scale campus deployment, exclusively for themselves. Information needed for implementation was published with informational status as RFC 7868 in 2016, which did not make it into an Internet Standards Track specification and allowed Cisco to retain control of the EIGRP protocol.

<span class="mw-page-title-main">Subnetwork</span> Logical subdivision of an IP network

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

<span class="mw-page-title-main">Classful network</span> Early system for organizing the IPv4 address space

A classful network is an obsolete network addressing architecture used in the Internet from 1981 until the introduction of Classless Inter-Domain Routing (CIDR) in 1993. The method divides the IP address space for Internet Protocol version 4 (IPv4) into five address classes based on the leading four address bits. Classes A, B, and C provide unicast addresses for networks of three different network sizes. Class D is for multicast networking and the class E address range is reserved for future or experimental purposes.

Dot-decimal notation is a presentation format for numerical data. It consists of a string of decimal numbers, using the full stop (dot) as a separation character.

In computer science, a mask or bitmask is data that is used for bitwise operations, particularly in a bit field. Using a mask, multiple bits in a byte, nibble, word, etc. can be set either on or off, or inverted from on to off in a single bitwise operation. An additional use of masking involves predication in vector processing, where the bitmask is used to select which element operations in the vector are to be executed and which are not.

A broadcast address is a network address used to transmit to all devices connected to a multiple-access communications network. A message sent to a broadcast address may be received by all network-attached hosts.

Longest prefix match refers to an algorithm used by routers in Internet Protocol (IP) networking to select an entry from a routing table.

<span class="mw-page-title-main">Supernetwork</span> Aggregation of Internet Protocol networks

A supernetwork, or supernet, is an Internet Protocol (IP) network that is formed by aggregation of multiple networks into a larger network. The new routing prefix for the aggregate network represents the constituent networks in a single routing table entry. The process of forming a supernet is called supernetting, prefix aggregation, route aggregation, or route summarization.

A default gateway is the node in a computer network using the Internet protocol suite that serves as the forwarding host (router) to other networks when no other route specification matches the destination IP address of a packet.

In network routing, the control plane is the part of the router architecture that is concerned with drawing the network topology, or the information in a routing table that defines what to do with incoming packets. Control plane functions, such as participating in routing protocols, run in the architectural control element. In most cases, the routing table contains a list of destination addresses and the outgoing interface(s) associated with each. Control plane logic also can identify certain packets to be discarded, as well as preferential treatment of certain packets for which a high quality of service is defined by such mechanisms as differentiated services.

Web Cache Communication Protocol (WCCP) is a Cisco-developed content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It has built-in load balancing, scaling, fault tolerance, and service-assurance (failsafe) mechanisms. Cisco IOS Release 12.1 and later releases allow the use of either Version 1 (WCCPv1) or Version 2 (WCCPv2) of the protocol.

route (command) Computer operating system command

In computing, route is a command used to view and manipulate the IP routing table in Unix-like and Microsoft Windows operating systems and also in IBM OS/2 and ReactOS. Manual manipulation of the routing table is characteristic of static routing.

IP routing is the application of routing methodologies to IP networks. This involves not only protocols and technologies but includes the policies of the worldwide organization and configuration of Internet infrastructure. In each IP network node, IP routing involves the determination of a suitable path for a network packet from a source to its destination in an IP network. The process uses static configuration rules or dynamically obtained from routing protocols to select specific packet forwarding methods to direct traffic to the next available intermediate network node one hop closer to the desired final destination, a total path potentially spanning multiple computer networks.

References