computer networking A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are m ...

, the default route is a configuration of the

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. I ...

(IP) that establishes a forwarding rule for packets when no specific address of a next-hop host is available from the

routing table 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 tho ...

or other routing mechanisms. The default route is generally the address of another router, which treats the packet the same way: if a route matches, the packet is forwarded accordingly, otherwise the packet is forwarded to the default route of that router. The route evaluation process in each router uses the

longest prefix match Longest prefix match (also called Maximum prefix length match) refers to an algorithm used by routers in Internet Protocol (IP) networking to select an entry from a routing table. Because each entry in a forwarding table may specify a sub-netwo ...

method to obtain the most specific route. The network with the longest

subnet mask A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. 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 ...

or network prefix that matches the destination

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

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 the latter case, the packet is dropped and an ICMP ''Destination Unreachable'' message may be returned. Each router traversal counts as one hop in the distance calculation for the transmission path. The device to which the default route points is often called the

default gateway 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. Role A gateway ...

, and it often carries out other functions such as packet filtering, firewalling, or

proxy server In computer networking, a proxy server is a server application that acts as an intermediary between a client requesting a resource and the server providing that resource. Instead of connecting directly to a server that can fulfill a reques ...

operations. The default route in

Internet Protocol Version 4 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 ...

(IPv4) is designated as the zero address, in CIDR notation. Similarly, in

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...

, the default route is specified by . The subnet mask is specified as , which effectively specifies all networks and is the shortest match possible. A route lookup that does not match any other rule falls back to this route. In the highest-level segment of a network, administrators generally point the default route for a given host towards the router that has a connection to a

network service provider Network Service Provider (NSP) is one of the roles defined in the National Information Infrastructure (NII) plan, which governed the transition of the Internet from US federal control to private-sector governance, with an accompanying shift from t ...

. Therefore, packets with destinations outside the organization's

LAN Lan or LAN may also refer to: Science and technology * Local asymptotic normality, a fundamental property of regular models in statistics * Longitude of the ascending node, one of the orbital elements used to specify the orbit of an object in spa ...

, typically destinations on the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...

or a

wide area network A wide area network (WAN) is a telecommunications network that extends over a large geographic area. Wide area networks are often established with leased telecommunication circuits. Businesses, as well as schools and government entities, us ...

, are forwarded to the router with the connection to that provider.

References

{{reflist Internet architecture Routing