Cisco Catalyst 3560-X Series, Software Configuration Manual

Page: 1137 / 1538

1-91
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-25303-03
Chapter 1 Configuring IP Unicast Routing
Configuring Unicast Reverse Path Forwarding
For more information about the information in the displays, see the Cisco IOS Switching Services
Command Reference, Release 12.4 .
Configuring Unicast Reverse Path Forwarding
The unicast reverse path forwarding (unicast RPF) feature helps to mitigate problems that are caused by
the introduction of malformed or forged (spoofed) IP source addresses into a network by discarding IP
packets that lack a verifiable IP source address. For example, a number of common types of
denial-of-service (DoS) attacks, including Smurf and Tribal Flood Network (TFN), can take advantage
of forged or rapidly changing source IP addresses to allow attackers to thwart efforts to locate or filter
the attacks. For Internet service providers (ISPs) that provide public access, Unicast RPF deflects such
attacks by forwarding only packets that have source addresses that are valid and consistent with the IP
routing table. This action protects the network of the ISP, its customer, and the rest of the Internet.
Note
Do not configure unicast RPF if the switch is in a mixed hardware stack combining more than one switch
type: Catalyst 3750-X, Catalyst 3750-E, and Catalyst 3750 switches.
For detailed IP unicast RPF configuration information, see the Other Security Features chapter in the
Cisco IOS Security Configuration Guide, Release 12.4 .
Configuring Protocol-Independent Features
This section describes how to configure IP routing protocol-independent features. These features are
available on switches running the IP base or the IP services feature set; except that with the IP base
feature set, protocol-related features are available only for RIP. For a complete description of the IP
routing protocol-independent commands in this chapter, see the “IP Routing Protocol-Independent
Commands” chapter of the
Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols,
Release 12.4.
• Configuring Distributed Cisco Express Forwarding, page 1-91
•
Configuring the Number of Equal-Cost Routing Paths, page 1-93
•
Configuring Static Unicast Routes, page 1-94
•
Specifying Default Routes and Networks, page 1-95
• Using Route Maps to Redistribute Routing Information, page 1-96
•
Configuring Policy-Based Routing, page 1-99
• Filtering Routing Information, page 1-103
•
Managing Authentication Keys, page 1-105
Configuring Distributed Cisco Express Forwarding
Cisco Express Forwarding (CEF) is a Layer 3 IP switching technology used to optimize network
performance. CEF implements an advanced IP look-up and forwarding algorithm to deliver maximum
Layer 3 switching performance. CEF is less CPU-intensive than fast switching route caching, allowing
more CPU processing power to be dedicated to packet forwarding. In a switch stack, the hardware uses
distributed CEF (dCEF) in the stack. In dynamic networks, fast switching cache entries are frequently