What is Gateway in Routing Table?

In a routing table, a gateway is the next hop router to which a device forwards traffic destined for a particular network or networks. It serves as an entry point to another network.

Here's a more detailed breakdown:

• Routing Table Basics: A routing table is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in many cases, metrics or distances associated with those routes. The routing table contains information necessary to forward a packet along the best path toward its destination.

• The Gateway's Role: When a device (e.g., a computer, router) needs to send data to a destination network not directly connected to it, it consults its routing table. If a route exists for that destination network, the routing table will specify the gateway. The device then forwards the data packet to that gateway router.

• Next Hop: The gateway entry in a routing table essentially defines the next hop. The current router doesn't need to know the entire path to the final destination. It only needs to know which router to send the packet to next. That next router, in turn, will make its own routing decision based on its routing table.

• Default Gateway: Often, a routing table includes a default gateway. This is the gateway used for traffic destined for any network not specifically listed in the routing table. If there's no specific route for the destination, the packet is sent to the default gateway. This is commonly seen on home networks where the router acts as the default gateway for all devices.

• Example:

  Let's say your computer's IP address is 192.168.1.100 and it needs to communicate with a server at 8.8.8.8 (Google's public DNS server). Your computer's routing table might look something like this (simplified):

  Destination Network	Gateway	Interface
  192.168.1.0/24	0.0.0.0	eth0
  0.0.0.0/0	192.168.1.1	eth0

  • 192.168.1.0/24: This is your local network. 0.0.0.0 for the gateway means it's directly connected (no gateway needed). The interface is eth0 (Ethernet interface).
  • 0.0.0.0/0: This is the default route (matches all destinations). The gateway is 192.168.1.1 (your router's IP address). The interface is eth0.

  Since 8.8.8.8 doesn't match the 192.168.1.0/24 network, your computer will use the default route and send the traffic to the gateway at 192.168.1.1. Your router (at 192.168.1.1) will then consult its routing table to determine where to send the traffic next, and so on, until the traffic reaches 8.8.8.8.

In summary, the gateway in a routing table is the address of the router to which a device sends packets destined for networks outside of its directly connected networks. It's crucial for enabling communication across different networks.