Editing Default route (section)

{{Use American English|date=January 2019}}{{Short description|Type of packet forwarding rule for networks
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{{Refimprove|date=December 2008}}

In [[computer networking]], the '''default route''' is a configuration of the [[Internet Protocol]] (IP) that establishes a forwarding rule for [[Packet (information technology)|packets]] when no specific address of a next-hop host is available from the [[routing table]] 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]] method to obtain the most specific route. The network with the longest [[Subnetwork mask|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 the latter case, the packet is dropped and an [[Internet Control Message Protocol#Destination unreachable|ICMP ''Destination Unreachable'']] message may be returned.<ref name='rfc792'>{{cite IETF|rfc=792|title=INTERNET CONTROL MESSAGE PROTOCOL, DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION|author=J. Postel|authorlink=John Postel||date=September 1981|publisher=Network Working Group}}</ref> 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]], and it often carries out other functions such as packet filtering, [[Firewall (networking)|firewalling]], or [[proxy server]] operations.

The default route in [[IPv4|Internet Protocol Version 4]] (IPv4) is designated as the zero address, {{IPaddr|0.0.0.0|0}} in [[CIDR notation]].<ref name='rfc4632'>{{cite IETF|rfc=4632|title=Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan|author1=V. Fuller|author2=T. Li|date=August 2006|publisher=Network Working Group|quote=Note that the degenerate route to prefix 0.0.0.0/0 is used as a default route and MUST be accepted by all implementations.}}</ref> Similarly, in [[IPv6]], the default route is specified by {{IPaddr|::|0}}. The subnet mask is specified as {{IPaddr||0}}, 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]]. Therefore, packets with destinations outside the organization's [[LAN]], typically destinations on the [[Internet]] or a [[wide area network]], are forwarded to the router with the connection to that provider.