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Network security is a hot topic today, and will only increase in importance in the months and years ahead.

While most of the attention is paid to exterior threats, there are some steps you can take to prevent unwanted Cisco router access from within your organization.

Whether you want to limit what certain users can do and run on your routers, or prevent unauthorized users in your company from getting to config mode in the first place, here are four important yet simple steps you can take to do so.

Encrypt the passwords in your running configuration.

This is a basic Cisco router security command that is often overlooked.  It doesn’t do you any good to set passwords for your ISDN connection or Telnet connections if anyone who can see your router’s running configuration can see the passwords.  By default, these passwords are displayed in your running config in clear text.

One simple command takes care of that.  In global configuration mode, run service password-encryption. This command will encrypt all clear text passwords in your running configuration.

Set a console password.

If I walked into your network room right now, could I sit down and start configuring your Cisco routers?

If so, you need to set a console password.  This password is a basic yet important step in limiting router access in your network.  Go into line configuration mode with the command “line con 0”, and set a password with the password command.

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From the CCNA to the CCIE, ISDN is one of the most important technolgies you’ll work with.  It’s also very common in the field  ISDN is frequently used as a backup connection in case an organization’s Frame Relay connections go down.  Therefore, it’s important to know ISDN basics not only for your particular exam, but for job success.

ISDN is used between two Cisco routers that have BRI or PRI interfaces.  Basically, with ISDN one of the routers places a phone call to the other router.  It is vital to understand not only what causes one router to dial another, but what makes the link go down.

Why?  Since ISDN is basically a phone call from one router to another, you’re getting billed for that phone call — by the minute.  If one of your routers dials another, and never hangs up, the connection can theoretically last for days or weeks.   The network manager then receives an astronomical phone bill, which leads to bad things for everyone involved!

Cisco routers use the concept of interesting traffic to decide when one router should call another.  By default, there is no interesting traffic, so if you don’t define any, the routers will never call each other.

Interesting traffic is defined with the dialer-list command.  This command offers many options, so you can tie interesting traffic down not only to what protocols can bring the link up, but what the source, destination, or even port number must be for the line to come up.

One common misconception occurs once that link is up.  Interesting traffic is required to bring the link up, but by default, any traffic can then cross the ISDN link.

What makes the link come down? Again, the concept of interesting traffic is used.  Cisco routers have an idle-timeout setting for their dialup interfaces.  If interesting traffic does not cross the link for the amount of time specified by the idle-timeout, the link comes down.

To summarize:  Interesting traffic brings the link up by default, any traffic can cross the link once it’s up a lack of interesting traffic is what brings the link down.

Just as important is knowing what keeps the link up once it is dialed. Why?  Because ISDN acts as a phone call between two routers, and it’s billed that way to your client.  The two routers that are connected by this phone call may be located in different area codes, so now we’re talking about a long distance phone call.
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Whenever a Cisco exam version changes, there’s always a lot of chatter about it on the web.  The CCNA exams are no exception.

One comment I see often goes like this: ” I hear Cisco is going to change Intro / ICND / CCNA exam versions soon, so I’m not going to start studying yet.  I’ll wait until the new exam comes out.”

Do not let this happen to you.

While some large publishers would have you think these exams change tremendously from one version to another (”updated for the latest exams!”), the simple fact is that the Intro, ICND, and CCNA Composite exams simply don’t change much from version to version.

Sure, the questions change. The only people who should be nervous about that are those who are trying to braindump their way to a technical certification.
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CCNA exam success depends greatly on knowing the details, and if there’s one protocol that has a lot of details, it’s OSPF!  This is true particularly of hub-and-spoke networks, so in this CCNA OSPF tutorial we’ll take a look at some of the more important hub-and-spoke OSPF details.  This will help you in working with real-world networks as well, since this OSPF network type is one of the more typical network topologies.

In OSPF, the hub must become the designated router (DR).  The DR election’s deciding value is the OSPF interface priority, and the default value is 1.  It’s not enough to set the hub’s OSPF interface to 2, however, since the spoke routers must not become the DR or BDR.  You must set the spoke interfaces to an OSPF priority of zero.

R2(config)#int s0

R2(config-if)#ip ospf priority 0

This ensures that the spokes will not become the DR or BDR if the hub goes down.

The hub does require a bit more configuration, though.  The neighbor command must be used on the hub to indicate the IP address of the potential neighbors.
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CCNA exam success depends on mastering many technologies that are new to you, and few exam topics have more details than ISDN.  ISDN isn’t just for your CCNA exam studies, though.  While ISDN is dismissed by many, the fact is that there are many small and mid-size networks out there that use ISDN as their backup to frame relay.  Some of these companies have spoke networks that use ISDN to connect to their hub as well, so it’s a great idea to know ISDN configuration and troubleshooting for your real-world career as well as passing the CCNA.  With that in mind, let’s take a look at five common ISDN errors and how to avoid them.

With dialer map statements, remember that the phone number you put in the dialer map is the phone number of the remote router, not the local one.  Look at it this way – if you want to call a friend on your cell, you don’t pick up your cell and dial your own number!

Speaking of dialer map statements, don’t forget the all-important broadcast option at the end of the command:

R1(config-if)#dialer map ip 172.12.21.1 name R2 broadcast 5555555

The router will accept that command without the “broadcast” option, but routing protocol updates and hellos would not be able to travel across the line.  (This command is also needed in frame relay map statements to allow broadcasts and multicasts to be transmitted.)

PAP is PPP’s clear-text authentication scheme, and clear text is a really bad idea.  But if you do have to configure it, don’t forget that PAP requires additional configuration -the ppp pap sent-username command.

R1(config-if)#ppp pap sent-username R1 password CISCO

Must set encapsulation to PPP before using PPP subcommands

R1(config-if)#
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