Types Of Routing - Cisco Catalyst 9500 series Configuration Manual

Configuring IP Unicast Routing
When Host A sends a packet to Host C in VLAN 20, Switch A forwards the packet to the router, which
receives the traffic on the VLAN 10 interface. The router checks the routing table, finds the correct outgoing
interface, and forwards the packet on the VLAN 20 interface to Switch B. Switch B receives the packet and
forwards it to Host C.

Types of Routing

Routers and Layer 3 switches can route packets in these ways:
• By using default routing
• By using preprogrammed static routes for the traffic
• By dynamically calculating routes by using a routing protocol
Default routing refers to sending traffic with a destination unknown to the router to a default outlet
or destination.
Static unicast routing forwards packets from predetermined ports through a single path into and out of a
network. Static routing is secure and uses little bandwidth, but does not automatically respond to changes in
the network, such as link failures, and therefore, might result in unreachable destinations. As networks grow,
static routing becomes a labor-intensive liability.
Dynamic routing protocols are used by routers to dynamically calculate the best route for forwarding traffic.
There are two types of dynamic routing protocols:
• Routers using distance-vector protocols maintain routing tables with distance values of networked
• Routers using link-state protocols maintain a complex database of network topology, based on the
Distance-vector protocols supported by the switch are Routing Information Protocol (RIP), which uses a single
distance metric (cost) to determine the best path and Border Gateway Protocol (BGP), which adds a path
vector mechanism. The switch also supports the Open Shortest Path First (OSPF) link-state protocol and
Enhanced IGRP (EIGRP), which adds some link-state routing features to traditional Interior Gateway Routing
Protocol (IGRP) to improve efficiency.
Classless Routing
By default, classless routing behavior is enabled on the Device when it is configured to route. With classless
routing, if a router receives packets for a subnet of a network with no default route, the router forwards the
packet to the best supernet route. A supernet consists of contiguous blocks of Class C address spaces used to
simulate a single, larger address space and is designed to relieve the pressure on the rapidly depleting Class
B address space.
resources, and periodically pass these tables to their neighbors. Distance-vector protocols use one or a
series of metrics for calculating the best routes. These protocols are easy to configure and use.
exchange of link-state advertisements (LSAs) between routers. LSAs are triggered by an event in the
network, which speeds up the convergence time or time required to respond to these changes. Link-state
protocols respond quickly to topology changes, but require greater bandwidth and more resources than
distance-vector protocols.
Routing Configuration Guide, Cisco IOS XE Everest 16.6.x (Catalyst 9500 Switches)
Types of Routing
53