39-95
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
OL-13270-06
Chapter 39 Configuring IP Unicast Routing
Configuring Unicast Reverse Path Forwarding
Configuring Unicast Reverse Path Forwarding
The Unicast Revse Path Forwarding (Unicast RPF) forwarding feature helps to mitigate problems that
are caused by the introduction of malformed or forged (spoofed) IP source addresses into a network.
Unicast RPF discards IP packets without a verifiable IP source address. For example, a number of
common denial-of-service (DoS) attacks, including Smurf and Tribal Flood Network (TFN), take
advantage of forged or rapidly changing source-IP addresses to allow attackers to avoid efforts to locate
or to filter the attacks. For Internet service providers (ISPs) that provide public access, Unicast RPF
deflects such attacks by forwarding only packets with valid source addresses and that are consistent with
the IP routing table. This action protects the network of the ISP, its customer, and the rest of the Internet.
For detailed IP Unicast RPFconfiguration information, see the
Other Security Features
section in the
Cisco IOS Security Configuration Guide, Release 12.2
.
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. However, on 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 12.2
from
the Cisco.com page under
Documentation
>
Cisco IOS Software
>
12.2 Mainline
>
Command
References
.
These sections contain this configuration information:
•
Configuring Cisco Express Forwarding and Distributed Cisco Express Forwarding, page 39-95
•
Configuring the Number of Equal-Cost Routing Paths, page 39-97
•
Configuring Static Unicast Routes, page 39-97
•
Specifying Default Routes and Networks, page 39-98
•
Using Route Maps to Redistribute Routing Information, page 39-99
•
Configuring Policy-Based Routing, page 39-103
•
Filtering Routing Information, page 39-106
•
Managing Authentication Keys, page 39-109
Configuring Cisco Express Forwarding and 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, providing
more CPU processing power dedicated to packet forwarding. In a switch stack, a stack member uses
distributed CEF (dCEF) in the stack. On a standalone switch , the switch uses CEF. In dynamic networks,
fast-switching cache entries are frequently invalidated because of routing changes, which causes traffic
to be process-switched using the routing table, instead of fast-switched using the route cache. CEF and
dCEF use the Forwarding Information Base (FIB) lookup table for destination-based switching of IP
packets.
