Overview
This lecture explains how routers forward packets between subnets, the role of routing tables, and introduces the concept and configuration of static routing.
Router Packet Forwarding Process
- Routers forward traffic between different IP subnets in home and office networks.
- A router identifies the destination IP address from each incoming packet.
- The router checks its routing table to determine the best route for the packet.
- If the destination is on a directly connected subnet, the packet is sent to that subnet.
- If the destination is not directly connected, the router forwards the packet to a "next hop" router.
- This process is repeated by each router until the packet reaches its final destination.
- If there is no matching route, the router discards the packet.
Routing Tables and Troubleshooting
- The routing table stores information on networks the router can reach and the associated next hops.
- Troubleshooting often involves checking the routing table and next hop entries.
- A complete and up-to-date routing table is critical for correct packet delivery.
Static Routing
- Static routing involves manually adding routes to the routing table by the network administrator.
- This method is fast and uses fewer resources (CPU, memory) compared to dynamic routing protocols.
- Static routing is common in small or remote networks, often called stub networks.
- Static routes require manual updates if network changes occur and do not adapt automatically.
- Misconfiguration can lead to routing loops or lost packets.
- Static routing is not scalable for large networks due to manual effort and risk of errors.
Configuring Static Routes: Example
- To reach networks behind other routers, static routes are manually added with the destination network and next hop IP address.
- For network 10.10.20.0/24 behind router 2, router 1 is configured to forward these packets to 10.10.40.2.
- For network 10.10.30.0/24 behind router 3, router 1 is configured to forward packets to 10.10.50.2.
Key Terms & Definitions
- Router — A device that forwards packets between IP subnets.
- Subnet — A segment of an IP network.
- Routing Table — A table containing routes to network destinations and instructions for packet forwarding.
- Next Hop — The next router to which a packet should be sent on its path to the destination.
- Static Routing — Manually configured routing entries that do not change automatically.
- Stub Network — A network with a single connection to an external network.
Action Items / Next Steps
- Review how to manually configure static routes on network routers.
- Prepare for a future lesson on dynamic routing protocols.