In a computer network, default route is the setting on the computer that defines the packet forwarding rules to use when no specific route can be specified for a particular Internet Protocol (IP) destination address. All packets for destinations that are not specified in the routing table are sent via the default route.
The default route generally points to another router, which treats the packets in the same way: if the route matches, the packet is passed accordingly, otherwise the packet is forwarded to the router's default route. Route evaluation process on each router using the longest prefix matching method to get the most specific route. The network with the longest subnet mask matching the destination IP address is the next-hop network gateway. This process will be repeated until the packet is sent to the destination. Each router traversal is calculated as a single hop in the distance calculation for the transmission path.
Devices where default route points are often called default gateways, and often perform other functions such as packet filtering, firewalls, or proxy server operations.
The default route in Internet Protocol Version 4 (IPv4) is designated as a zero-address 0.0.0.0/0 in CIDR notation, often called the quad-zero route. The subnet mask is given as/0, which effectively determines all networks, and is the shortest possible match. Searching for routes that do not match other routes, return to this route. Similarly, in IPv6, the default route is determined by ::/0 .
In the highest-level segment of a network, administrators generally designate a default route for a given host to a router that has a connection to the network service provider. Therefore, packets with destinations outside the organization's local area network, usually destinations on the Internet or a wide area network, are forwarded to the router with connections to that provider.
Video Default route
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Source of the article : Wikipedia
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