14.6.2 Module Quiz: Routing Concepts Flashcards

Study Notes

This module explains how routers use information in packets to make forwarding decisions.
Routers determine the best path and forward packets to their destinations.
Basic router configuration settings and routing table structure are covered.
Static and dynamic routing concepts are compared.

A router, when receiving an IP packet, determines which interface to use for forwarding to the destination.
Routing involves choosing the best interface, either for the final destination or for another router connection to reach the destination network.
The main functions of a router are to determine the best path and forward packets to a destination interface.
This is done based on the information in the routing table.

Packet forwarding begins when a data link frame, encapsulating an IP packet, arrives on an ingress interface.
The router then checks the destination IP address and consults its routing table.
It finds the longest matching prefix in the table that matches the destination IP address in the packet header.
The router encapsulates the packet in a data link frame and forwards it to the egress interface.
The destination can either be a device or a next-hop router from the network to which it is attached.
If there is no match found, the packet is dropped.

The topology will be used with configuration and verification examples for discussion of the IP routing table. (figure is referenced)

A routing table is a list of routes to known networks, consisting of prefixes and their lengths.
Directly connected networks and static routes provide routing information.
Dynamic protocols also provide this info to reach a remote network.
Common codes such as L for interface assigned addresses, C for directly connected networks, S for static routes, and O for dynamically learned routes from other routers are used to identify sources of routing table entries.

Static routes are used in scenarios like default paths to service providers, when dynamic protocols don't learn about routes, when an administrator wants to explicitly define the path, and for routing between stub networks.
Dynamic routing protocols, such as OSPF, are used in situations where the network is larger and needs its routes to automatically learn about new networks and adjust when the network topology changes.
A dynamic routing protocol considers factors like metrics to determine the best path.

The module covers the primary functions in routing table information to determine the best path, the longest matching route.
Directly connected networks are added to the routing table when the interface is active. A router can receive a routing update and consult the table.
Routers can learn about remote networks via static routes or through protocols.
Routers are able to forward packets to a next-hop router, locally connected device, or drop the packet.
There are various configuration and verification commands for routers, including show ip route, show ip interface, and show ip interface brief.