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IP Routing Overview
Go to these sections for information you are interested in:
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Routing
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Routing Protocol Overview
Displaying and Maintaining a Routing Table
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The term “router” in this document refers to a router in a generic sense or a Layer 3 switch.
Rou
an optimal
outer in the path until the
packet reaches the last router, which forwards the packet to the intended destination host.
ation that guides the forwarding of packets.
Routi
n bases (FIBs) play a key role
a
ries by origin:
e routes.
cifies which physical interface a packet destined for a certain destination
hop (the next router) or the directly connected destination.
Introduction to routing t
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
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ting
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
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
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Direct routes: Routes discovered by data link protocols, also known as interfac
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Static routes: Routes that are manually configured.
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Dynamic routes: Routes that are discovered dynamically by routing protocols.
Each entry in the FIB table spe
should go out to reach the next
able
Each router maintains a local r
table.
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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
