IP Routing Overview
Go to these sections for information you are interested in:
Routing Protocol Overview
Displaying and Maintaining a Routing Table
The term "router" in this document refers to a router in a generic sense or a Layer 3 switch.
Routing in the Internet is achieved through routers. Upon receiving a packet, a router finds
route based on the destination address and forwards the packet to the next r
packet reaches the last router, which forwards the packet to the intended destination host.
Routing provides the path inform
ng Table and FIB Table
Routing tables play a key role in route selection and forwarding informatio
in p cket forwarding. Each router maintains a routing table and a FIB table at least.
Routes in a routing table can be divided into three catego
Direct routes: Routes discovered by data link protocols, also known as interfac
Static routes: Routes that are manually configured.
Dynamic routes: Routes that are discovered dynamically by routing protocols.
Each entry in the FIB table spe
should go out to reach the next
Introduction to routing t
Each router maintains a local r
Routing table of a protocol
A protocol routing table stores routes discovered by the routing protocol.
A routing protocol can re
OSPF can redistribute dire
advertise those routes.
Local routing table
ation that guides the forwarding of packets.
cifies which physical interface a packet destined for a certain destination
hop (the next router) or the directly connected destination.
outing table. Each routing protocol also maintains a protocol routing
distribute and advertise routes generated by other protocols. For example,
ct routes, static routes and IS-IS routes to the OSPF routing table and then
outer in the path until the
n bases (FIBs) play a key role
ries by origin: