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Default gateway

A default gateway is the network node (usually a router) that forwards packets from a local subnet to other networks; hosts use it as the next hop for destinations outside the local network.

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Overview

A default gateway is the IP address of a router or routing device that a host uses to send traffic destined for addresses outside the host's local subnet. When a computer determines that a destination is not on its local network it forwards the packet to the default gateway, which forwards it onward toward the destination. The term is often used interchangeably with "default route" or "gateway of last resort."

How it works

Hosts consult their routing table to decide whether a destination is local. If no specific route exists, the default route (typically 0.0.0.0/0 for IPv4 or ::/0 for IPv6) points to the default gateway as the next hop. Before sending a frame on an Ethernet network the host resolves the gateway's MAC address using ARP (Address Resolution Protocol). The gateway then handles further routing, which may include passing packets to other routers or to the Internet.

Configuration and examples

Default gateways can be set manually on a device or assigned dynamically by DHCP. Common local gateway addresses used in small networks include examples such as 192.168.1.1, but any routable address on the host's subnet may serve. Network administrators can find and verify the configured gateway with platform-specific tools such as ip route or route commands on many systems.

Uses and importance

The default gateway is essential for general connectivity beyond the local segment: web browsing, email, and services hosted on other networks all rely on a correct gateway. In more complex networks multiple gateways and policy-routing rules can direct traffic differently based on source, destination, or type of service, and load balancers or firewalls often act as the first-hop gateway.

Notable distinctions and troubleshooting

  • The default gateway is distinct from DNS: the gateway forwards packets, while DNS resolves names to addresses.
  • If a host cannot reach other networks, common troubleshooting steps include pinging the gateway, checking the local route table, and verifying ARP entries.
  • Some systems support several gateways or fallback gateways; however, ordinary hosts normally use a single configured default gateway.

Further reading

For background on addressing and routing basics see documentation on IP addressing, and for diagrammatic explanations of traffic flow consult network diagrams that illustrate local subnets, routers and default routes.

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AlegsaOnline.com Default gateway

URL: https://en.alegsaonline.com/art/26246

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