132 Chapter 4 Cisco Perimeter Router Problems and Solutions

Summary

You’re now familiar with the Cisco IOS Firewall software and some of its features, and you’re aware of the dangers lurking at the perimeter of your network. You also learned about ways to keep your network and its data safe using features built into the Cisco IOS Firewall.

By matching each problem with a specific solution, you’re now equipped with strategies that you can use against those attacks. Remember that the solution for eavesdropping and session replay is using encryption schemes such as IPSec. To stop unauthorized users from accessing your network, some simple access control lists work just fine. To provide relief from an IP address shortage, use NAT on the perimeter router to conserve subnets. The best solution for rerouting attacks is to configure MD5 authentication on your router. And finally, the solution for DoS attacks is to use the TCP Intercept feature.

If you brilliantly configure these features at the perimeter of your network, you’re good and safe to go. And a router running the Cisco IOS Firewall software can do all of this for you.

Exam Essentials

Know the solution to eavesdropping. To prevent eavesdropping, use IPSec encryption.

Know the commands to stop a chargen attack. The following two commands can stop a chargen attack:

Lab_B(config)#no service tcp-small-servers

Lab_B(config)#no service udp-small-servers

Know how to prevent unauthorized access, data manipulation, and malicious destruction.

To prevent certain inbound and outbound packets, use ACLs.

Know the solution to the lack of legal IP addresses problem. If you do not have enough legal IP addresses, use NAT and PAT.

Know how to prevent rerouting attacks. To secure your network against rerouting attacks, enable MD5 authentication.

Know how to prevent DoS attacks. To prevent DoS attacks, enable TCP Intercept.

Commands Used in This Chapter 133

Key Terms

Before you take the exam, be certain you are familiar with the following terms:

Commands Used in This Chapter

Here is the list of commands used in this chapter:

134 Chapter 4 Cisco Perimeter Router Problems and Solutions

Written Lab

This section asks you 10 write-in-the-answer questions to help you understand the technology that you need to know in order to pass the MCNS exam.

1.Which TCP Intercept mode will proxy-answer incoming SYN requests and not notify the server until the originating host is verified?

2.Which command would you configure on the perimeter router if you do not want it to announce to external hosts which subnets are not configured?

3.You want to disable Finger replies on a perimeter router. Which command do you want to use?

4.Which two commands would you use on your router to prevent a chargen attack?

5.___________ can be used to encrypt data between two networks, which prevents eavesdropping.

6.In a rerouting attack, the ___________ table is modified or prevented from being updated.

7.Which command disables Cisco Discovery Protocol on a perimeter router?

8.What command is used to enable an HTTP server on a router for AAA?

9.Which command disables Cisco Discovery Protocol on a perimeter router interface?

10.What command will disable proxy ARP on a perimeter router?