Configuring the NAS for AAA

Sometimes people call bastions sacrificial hosts because the odds are so good that they’ll be attacked. If you’re thinking that it might be a good idea to offer the bastion host a little backup, you’re on the right track. Because they have only one network interface card (NIC), bastion hosts are vulnerable to IP spoofing attacks. But if you put a bastion host between two routers, you can configure it so that one router filters requests from untrusted networks, while the other router filters requests coming in from trusted networks, thus preventing spoofed packets from reaching your bastion host at all. Your routers verify that any network traffic traveling between them is addressed only to the bastion host. Most of the time, you’ll find all-purpose operating systems such as Windows NT, Unix, or VMS running on a bastion host.

Here’s another term—the dirty DMZ. Sounds really cool, huh? It’s basically just a LAN inside your network that uses real Internet IP addresses. Don’t confuse a dirty DMZ with a protected DMZ LAN. A DMZ LAN is connected to the inside of the Private Internet eXchange (PIX) and uses private IP addresses instead.

I know it’s different, but in the example in the preceding graphic, the dirty DMZ has private IP addresses. That’s only because it makes illustrating this configuration easier for the purposes of this book. Just know that your real-world dirty DMZ would have real IP addresses and would be much more vulnerable to attacks than a protected DMZ would be.

Configuring the NAS for AAA

Okay, keeping in mind all you’ve learned so far, it’s time to show you how to configure the NAS to perform AAA using a local database. If you consider that every router is a target, then you must also understand that all interfaces on the NAS are at risk.

Here are the steps you must take to configure the NAS for AAA:

Secure access to the exec mode with your character-mode passwords.

Enable AAA locally on the NAS.

Configure authentication on the NAS.

Configure authorization on the NAS.

Configure accounting on the NAS.

Verify your NAS configuration.

Troubleshoot AAA on the Cisco NAS.

Securing Access to the Exec Mode

To secure access to the exec modes, set your character-mode passwords first. Keep in mind that there are two access modes to consider when configuring the NAS: character-mode access and

42 Chapter 2 Introduction to AAA Security

packet-mode access. Table 2.2 lists the different access modes, the port types, and the AAA commands.

T A B L E 2 . 2 NAS Character and Packet Modes

Earlier in this chapter, you learned how to set your line passwords on the console, VTY, and AUX ports, but you still need to set your enable password. This is done using the following commands:

Todd#config t

Enter configuration commands, one per line. End with CNTL/Z. Todd(config)#enable secret globalnet

Todd(config)#enable password globalnet

The enable password you have chosen is the same as your enable secret. This is not recommended. Re-enter the enable password. Todd(config)#enable password routersim

Todd(config)#

The best command for this task is the enable secret command because it automatically encrypts the password and supercedes the enable password. The two passwords cannot be the same.

Password Encryption

Because the enable password isn’t encrypted by default, it’s best to just use the enable secret command. By default, those line passwords aren’t encrypted either.

So use the following command to encrypt your router passwords:

Todd(config)#service password-encryption

Todd(config)#^Z (Ctrl+Z)

Todd#show running-config

Current configuration:

!

hostname Todd

!

enable secret 5 $1$Qrnt$AmoVOSoe/ImPuv6jN9PeL. enable password 7 06140034584B1B0A0C1A

!

[output cut] line con 0

password 7 104D000A0618 login

transport input none line aux 0

password 7 0958410D1D login

line vty 0 4

password 7 082D4D43041500 login

Once you’ve turned this command on, you need to exit from the global configuration mode and enter the show running-config command to see that the passwords are now encrypted.

At this point, turn off the service password-encryption command by using the no servicepassword encryption command as follows because the service password-encryption command is still running in the background, and no one needs any extra threads taking up CPU cycles:

Todd#config t

Enter configuration commands, one per line. End with CNTL/Z.

Todd(config)#no service password-encryption

Todd(config)#^Z

Todd#

In addition to adding the character-mode passwords, you can set a username and password for each user by using the username command as follows:

Todd(config)#username todd password lammle

Todd(config)#line con 0

Todd(config-line)#login local

Todd(config-line)#line aux 0

Todd(config-line)#login local

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Todd(config-line)#line vty 0 4

Todd(config-line)#login local

The router will now prompt for a username and password when a login attempt is made:

Todd con0 is now available

Press RETURN to get started.

User Access Verification

Username: todd

Password: (not displayed)

Todd>en

Password: (not displayed)

Todd#

You can now set up access for each user individually and define different levels of access for each user.

Enable AAA Locally on the NAS

You can also set up authorization, authentication, and accounting (AAA) on the router, which we’ll call an NAS from here on out. After you set the character-mode passwords to secure access to the exec mode, you then need to enable AAA globally on the NAS. It’s a pretty simple process:

Todd#config t

Enter configuration commands, one per line. End with CNTL/Z. Todd(config)#aaa ?

new-model Enable NEW access control commands and functions.(Disables OLD commands.)

Todd(config)#aaa new-model

Todd(config)#aaa ?