38-3
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
OL-12247-04
Chapter 38 Configuring IP Unicast Routing
Understanding IP Routing
•
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 it does not automatically respond to
changes in the network, such as link failures. Therefore, network changes might result in unreachable
destinations. As networks grow, static routing becomes a labor-intensive liability.
Routers use these dynamic routing protocols to dynamically calculate the best route for forwarding
traffic:
•
Routers that use distance-vector protocols maintain routing tables with distance values of networked
resources and periodically pass these tables to their neighbors. Distance-vector protocols use one or
a series of metrics for calculating the best routes.
•
Routers using link-state protocols maintain a complex database of network topology based on the
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.
Distance-vector protocols supported by the switch use Routing Information Protocol (RIP), a
single-distance metric (cost) that determines 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.
Note
On a switch or switch stack, the supported protocols are determined by the software running on the
switch or stack master. If the switch or stack master is running the IP base feature set, only default
routing, static routing and RIP are supported. All other routing protocols require the IP services feature
set.
IP Routing and Switch Stacks
A switch stack appears to the network as a single router, regardless of which switch in the stack is
connected to a routing peer. For additional information about switch stack operation, see
The stack master performs these functions:
•
It initializes and configures the routing protocols.
•
It sends routing protocol messages and updates to other routers.
•
It processes routing protocol messages and updates received from peer routers.
•
It generates, maintains, and distributes the distributed Cisco Express Forwarding (dCEF) database
to all stack members. The routes are programmed on all switches in the stack bases on this database.
•
The MAC address of the stack master is used as the router MAC address for the whole stack, and all
outside devices use this address to send IP packets to the stack.
•
All IP packets that require software forwarding or processing go through the CPU of the stack
master.
