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26 Chapter 1 Introduction to Network Security

Answers to Written Lab

1.Network snooping and packet sniffing are two common terms for eavesdropping.

2.Policy, technology, and configuration weaknesses are the three typical security weaknesses in a network implementation.

3.Improper change control and no disaster recovery plan demonstrate policy weaknesses.

4.A masquerade attack is when an attacker tries to steal an IP address.

5.Unsecured user accounts are an example of configuration weakness.

6.TCP/IP weaknesses, operating system weaknesses, and network equipment weaknesses are three technology weaknesses that can affect security.

7.No disaster recovery plan and high turnover in the technical support department are examples of policy weaknesses.

8.Session replaying, SNMP, and SMTP are examples of TCP/IP weaknesses.

9.Cisco Lock-and-Key, CHAP, and TACACS+ are three options for countering an unauthorized access attempt.

10.The TCP Intercept feature protects a server from TCP SYN-flooding attacks.

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Answers to Review Questions

27

Answers to Review Questions

1.D, E. Cisco describes the absence of a disaster recovery plan and a high turnover rate in the technical support department as policy weaknesses.

2.A, B, D. Policy, technology, and configuration weaknesses are the three typical weaknesses in a network implementation.

3.C, E, F. There are many problems with the IP stack, especially in Microsoft products. Session replaying is a weakness that is found in TCP. Both SNMP and SMTP are identified by Cisco as inherently insecure protocols in the TCP/IP stack.

4.B. The TCP Intercept feature implements software to protect TCP servers from TCP SYN-flooding attacks, which are a type of denial-of-service attack.

5.B, E, G. By using the Cisco Lock-and-Key along with CHAP and TACACS+, you can create a more secure network and help prevent unauthorized access.

6.A, D, F. The security challenge facing enterprises today is one of sorting through a wide range of solutions and choosing the right combination. A vast quantity of security technologies exist. It is not the lack of technology that makes securing the network difficult; the problem is choosing among the many different selections available and adopting those that satisfy your unique network and business requirements.

7.C. Network snooping and packet sniffing are common terms for eavesdropping.

8.A, F. Misconfigured network equipment is a configuration weakness. However, that is the first answer most people would pick for this question. A consistent security policy is not a weakness, and IP spoofing and masquerade attacks are not security policy weaknesses.

9.C. IP spoofing is fairly easy to stop once you understand the way spoofing takes place. An IP spoofing attack occurs when an attacker outside your network pretends to be a trusted computer by using an IP address that is within the range of IP addresses for your network. The attacker wants to steal an IP address from a trusted source so they can use it to gain access to network resources.

10.B, D. Taking the time to create a security policy is worth the time, money, and effort. For this question, the proper answers are that a security policy provides a process to audit existing network security and defines which behavior is and is not allowed.

11.B, C. Possible configuration weaknesses in a corporate network include unsecured user accounts, system accounts with easily guessed passwords, misconfigured Internet services, unsecured default settings in products, and misconfigured network equipment.

12.A, C, D. Possible policy weaknesses include the absence of a security policy; organization politics; lack of business continuity; the inability of the organization to implement policy evenly; improper change controls; logical access controls not being applied; lax security administration, including monitoring and auditing; software and hardware installation and changes that don’t follow the stated installation policy; and the absence of a disaster recovery plan.

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28 Chapter 1 Introduction to Network Security

13.B, C, D. TCP/IP protocol weaknesses, operating system weaknesses, and network equipment weaknesses are identified by Cisco as the three technology weaknesses.

14.A, C, D. Passwords, firewalls, and authentication, as well as routing protocols, should have policies in place before any network equipment is configured and installed.

15.B. Possible configuration weaknesses in a corporate network include unsecured user accounts, system accounts with easily guessed passwords, misconfigured Internet services, unsecured default settings in products, and misconfigured network equipment.

16.C. Possible policy weaknesses include the absence of a security policy; organization politics; lack of business continuity; inability of the organization to implement policy evenly; improper change controls; logical access controls not being applied; lax security administration, including monitoring and auditing; software and hardware installation and changes that don’t follow the stated installation policy; and the absence of a disaster recovery plan.

17.A. TCP/IP protocol weaknesses, operating system weaknesses, and network equipment weaknesses are identified by Cisco as the three technology weaknesses.

18.C. Possible policy weaknesses include the absence of a security policy; organization politics; lack of business continuity; inability of the organization to implement policy evenly; improper change controls; logical access controls not being applied; lax security administration, including monitoring and auditing; software and hardware installation and changes that don’t follow the stated installation policy; and the absence of a disaster recovery plan.

19.C. Possible policy weaknesses include the absence of a security policy; organization politics; lack of business continuity; inability of the organization to implement policy evenly; improper change controls; logical access controls not being applied; lax security administration, including monitoring and auditing; software and hardware installation and changes that don’t follow the stated installation policy; and the absence of a disaster recovery plan.

20.C. Possible policy weaknesses include the absence of a security policy; organization politics; lack of business continuity; inability of the organization to implement policy evenly; improper change controls; logical access controls not being applied; lax security administration, including monitoring and auditing; software and hardware installation and changes that don’t follow the stated installation policy; and the absence of a disaster recovery plan.

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Chapter

Introduction to AAA

2

Security

 

THE FOLLOWING SECUR EXAM TOPICS ARE

 

COVERED IN THIS CHAPTER:

 

Securing network access using AAA

 

Authentication methods

 

Configuring local AAA

 

Verifying AAA

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In only a few short years, network security has grown from a consideration into a vital and critically important essential for network administrators. In an age of increasing dependence on and

use of the Internet, nearly everyone—from individuals and small businesses to huge corporations, institutions, and worldwide organizations—is now a potential victim of hackers and E-crime. Although the defense techniques continue to improve with time, so does the sophistication and weaponry used by the bad guys. Today’s tightest security will be laughably transparent three years from now, making it seriously necessary for an administrator to keep current with the industry’s quickly evolving security trends.

Solid security hasn’t just become a valuable requirement; it’s also becoming increasingly complex and multi-tiered. Cisco continues to develop and extend its features to meet these demands by providing you with sharp tools like the Network Access Server (NAS). The NAS isn’t a real physical server; it’s actually a platform created to connect an interface between the packet world and the circuit world.

Authentication, Authorization, and Accounting (AAA) services are part of the Cisco NAS interface. This technology gives you substantial control over users and what those users are permitted to do inside of your networks. And there are more tools in the shed; RADIUS and TACACS+ security servers help you implement a centralized security plan by recording network events to the security server or to a Syslog server via logging.

I know this sounds pretty complicated, and, truthfully, it is. But that’s why I’m devoting an entire chapter to explaining these things to you!

I’ll start with a brief introduction to Cisco NAS and AAA security. And because it’s so important to understand how to properly authenticate users on a network, I’m going to discuss the various ways—good and bad—to do that. Then I’m going to cover the ins and outs (pun intended, sorry) of granting permissions and recording activity. And finally, I’ll get you into the real goods— describing the more advanced aspects of Cisco NAS and AAA, including how to configure them.

Understanding Network Access Server

and Cisco AAA

Before I explain AAA, it’s really important that you understand and remember that Cisco’s NAS is not an actual physical server. It’s actually a router with a database; the server is configured and exists within that router’s database. It’s this feature—this configuration—that gives you the

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Understanding Network Access Server and Cisco AAA

31

ability to add authentication, authorization, and accounting services to your router so you can provide and apply security where and how you need it—nice! Okay, great. You’re asking, “So how do you configure NAS commands on a Cisco router, and when are you going to show me?” Right now! I’ll explain how to do this and show you how to provide local (AAA) security for an NAS router. Let’s get started.

One of the things that’s so sweet about AAA architecture is that it enables systematic access security both locally and remotely! AAA technologies work within the remote client system, the NAS, and the security server to secure dial-up access. Here’s a definition of each of the As in AAA:

Authentication Authentication requires users to prove that they are who they say they are in one of these three ways:

Name and password

Challenge and response

Token cards

Authorization Authorization takes place only after authentication has validated the user. Authorization provides the needed resources specifically allowed to the user and permits the operations that the user is allowed to perform.

Accounting AAA’s accounting and auditing function records what the users actually do on the network and which resources they access. It also keeps track of how much time they spend using network resources for accounting and auditing purposes.

The most common form of router authentication is known as line authentication, also known as character-mode access. Line authentication uses different passwords to authenticate users, depending on the line the user is connecting through.

You can protect character-mode access to network equipment through a Cisco router as described in Table 2.1.

T A B L E 2 . 1

Local Line Types

 

 

Line Type

Description

 

 

AUX

Auxiliary EIA/TIA-232 DTE port on Cisco routers and Ethernet switches.

 

Used for modem-supported remote control and asynchronous routing up

 

to 38.4Kbps.

Console

Console EIA/TIA-232 DCE port on Cisco routers and Ethernet switches.

 

Used for asynchronous access to device configuration modes.

TTY

Standard EIA/TIA-232 DTE asynchronous line on an NAS.

VTY

Virtual terminal line and interface terminating incoming character streams

 

that do not have a physical connection to the access server or the router.

 

 

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