Networks Articles

Computers » Networks | By Chris Bryant @ Wednesday, 5th April 2006 @ 8:56 AM

Access Control Lists (ACLs) allow a router to permit or deny packets based on a variety of criteria. The ACL is configured in global mode, but is applied at the interface level. An ACL does not take effect until it is expressly applied to an interface with the ip access-group command. Packets can be filtered as they enter or exit an interface. If a packet enters or exits an interface with an ACL applied, the packet is compared against the criteria of the ACL. If the packet matches th... more...

Computers » Networks | By Chris Bryant @ Tuesday, 4th April 2006 @ 11:12 AM

Your BSCI exam and CCNP certification success depend on mastering BGP, and a big part of that is knowing how and when to use the many BGP attributes. And for those of you with an eye on the CCIE, believe me - you've got to know BGP attributes like the back of your hand. One such BGP attribute is the Multi-Exit Discriminator, or MED. The MED attribute is sent from a router or routers in one AS to another AS to indicate what path the remote AS should use to send data to the local AS. <... more...

Computers » Networks | By Chris Bryant @ Tuesday, 4th April 2006 @ 9:18 AM

In this CCNA case study, we'll take some basic switching and trunking theory and put it into action. We have two routers (R2 and R3) along with two switches (SW1 and SW2). R2 is connected to SW1 at fast 0/2, and R3 is connected to SW2 at fast 0/3. Both routers have IP addresses on the 172.12.23.0 /24 network. For these routers to be able to ping each other, the switches must be able to communicate. These are two 2950 switches, and they're connected via two crossover cables. ... more...

Computers » Networks | By Chris Bryant @ Monday, 3rd April 2006 @ 11:55 AM

As a CCNP candidate and a CCNA, you may be tempted to skip or just browse the many details of Spanning Tree Protocol. After all, you learned all of that in your CCNA studies, right? That's right, but it never hurts to review STP for a switching exam! Besides, many of us think of the four STP port states - but officially, there's a fifth one! Disabled isn't generally thought of as an STP port state, but Cisco does officially consider this to be an STP state. A disabled po... more...

Computers » Networks | By Chris Bryant @ Monday, 3rd April 2006 @ 11:55 AM

As a CCNA candidate, you most likely have some background in PC hardware and workstation support. If so, you're already familiar with loopback interfaces, particularly 127.0.0.1, the loopback address assigned to a PC. When you're learning all about the different physical interfaces for your CCNA exam - serial, ethernet, and BRI, among others - there's one logical interface you need to know about, and that is - you guessed it! - the loopback interface. What isn'... more...

Computers » Networks | By Chris Bryant @ Monday, 3rd April 2006 @ 11:55 AM

As a CCNP candidate, as a CCNA, and in getting ready to pass the BSCI exam, you may be tempted to breeze through your static route studies, or even skip them! That's because static routes are easy enough to configure, and as long as you remember the syntax of the ip route command, you're in good shape. But there's one vital detail regarding static routes that many exam candidates miss. That's because many CCNA and CCNP books say "the administrative distance of a s... more...

Computers » Networks | By Chris Bryant @ Saturday, 1st April 2006 @ 11:57 AM

DNS behaviors of a Cisco router are important topics for both the CCNA exam and real-world production networks, and you probably didn't know there were so many DNS details before you began studying for the exam! In this tutorial, we'll look at the ip name-server command and its proper usage. When a command is mistyped on a Cisco router, the default behavior of the router is to attempt to resolve it via DNS. First, the router looks for an IP Host table on the local router to perf... more...

Computers » Networks | By Chris Bryant @ Saturday, 1st April 2006 @ 11:57 AM

In your BCMSN / CCNP exam study, it's easy to overlook some of the details of Spanning Tree Protocol (STP). After all, you learned all of that in your CCNA studies, right? Not necessarily! While some of the BCMSN material will be a review for you, there are some details regarding familiar topics that you need to learn. That includes the timers for STP - Hello Time, MaxAge, and Forward Delay. You may remember these timers from your CCNA studies as well, and you should also remember th... more...

Computers » Networks | By Chris Bryant @ Saturday, 1st April 2006 @ 11:56 AM

To be successful on the BSCI exam and in earning your CCNP, you've got to master route redistribution. This isn't as easy as it sounds, because configuring route redistribution is only half the battle. Whether it's on an exam or in a real-world production network, you've got to identify possible points of trouble before you configure route redistribution - and you need to be able to control redistribution as well. You may have an OSPF domain with 100 routes, but only need to ... more...

Computers » Networks | By Chris Bryant @ Friday, 31st March 2006 @ 10:56 AM

Your BCMSN and CCNP studies will include mastering the details of Spanning Tree Protocol (STP). While you learned some of these details in your CCNA studies, quite a bit of it may be new to you. Before going on to the intermediate and advanced STP features, let's review the root bridge election process and learn how to change these results. Each switch will have a Bridge ID Priority value, more commonly referred to as a BID. This BID is a combination of a default priority value and t... more...

Computers » Networks | By Chris Bryant @ Friday, 31st March 2006 @ 10:55 AM

It might happen on your CCNA exam, it might happen on your production network - but sooner or later, you're going to have to perform password recovery on a Cisco router or switch. This involves manipulating the router's configuration register, and that is enough to make some CCNA candidates and network administrators really nervous! It's true that setting the configuration register to the wrong value can damage the router, but if you do the proper research before starting ... more...

Computers » Networks | By Chris Bryant @ Thursday, 30th March 2006 @ 8:55 AM

To pass the BSCI exam, earn your CCNP certification, and become an outstanding networker, you've got to master the many details of BGP - and trust me, there are a lot of details to master! Before you get into the more advanced features of BGP, you should have the fundamentals down cold, and one of those fundamentals is knowing the BGP adjacency states. This will allow you to successfully analyze and troubleshoot BGP peer relationships. In the following example, a BGP peering is b... more...

Computers » Networks | By Chris Bryant @ Thursday, 30th March 2006 @ 8:55 AM

One of the first things you do when you start studying for the CCNA exam is memorizing a list of port numbers and the protocols that run on those ports. If you're an experienced networker, you know most of the protocols that are mentioned - DNS, DHCP, FTP, SMTP, and so on. But there's one protocol that you might not have experience with, but is actually vital for CCNA exam success and success in working with Cisco routers and switches, and that's TFTP - Trivial File Transfer Proto... more...

Computers » Networks | By Chris Bryant @ Wednesday, 29th March 2006 @ 9:55 AM

To pass the CCNA exam, you've got to create a study plan. Part of that plan is scheduling your study time, and making that study time count. You’ve scheduled your exam you’ve created a document to track your study time you’ve planned exactly when you’re going to study. Now the plan must be carried out, without exception. What exceptions do I mean? Cell phones. Televisions. IPods. Significant others. The list can go on and on. It’s one thing to have a plan, a... more...

Computers » Networks | By Chris Bryant @ Tuesday, 28th March 2006 @ 2:58 PM

When you earned your CCNA, you thought you learned everything there is to know about RIP. Close, but not quite! There are some additional details you need to know to pass the BSCI exam and get one step closer to the CCNP exam, and one of those involves RIP update packet authentication. You're familiar with some advantages of using RIPv2 over RIPv1, support for VLSM chief among them. But one advantage that you're not introduced to in your CCNA studies is the ability to configure ... more...

Computers » Networks | By Chris Bryant @ Monday, 27th March 2006 @ 1:56 PM

Passing the BCMSN exam and getting one step closer to the CCNP certification means learning and noticing details that you were not presented with in your CCNA studies. (Yes, I know – you had more than enough details then, right?) One protocol you’ve got to learn more details about is VTP, which seemed simple enough in your CCNA studies! Part of learning the details is mastering the fundamentals, so in this tutorial we’ll review the basics of VTP. In show vtp status readouts, the &q... more...

Computers » Networks | By Chris Bryant @ Monday, 27th March 2006 @ 1:55 PM

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 ... more...

Computers » Networks | By Chris Bryant @ Wednesday, 22nd March 2006 @ 8:55 AM

CCNA exam success depends largely on noticing the details, and this is especially true of configurations involving directly connected serial interfaces. And of course, it's not enough to notice these details - you've got to know what to do about them! A Cisco router is a DTE by default, but directly connecting two DTEs with a DCE/DTE cable is not enough. In the following example, R1 and R3 are directly connected at their Serial1 interfaces. The line goes up briefly after bein... more...

Computers » Networks | By Chris Bryant @ Wednesday, 22nd March 2006 @ 8:55 AM

Your BSCI and CCNP exam success depends on knowing the details, and one such detail is knowing the proper way to summarize routes in OSPF. Route summarization is not just a test of your binary conversion abilities, but knowing where and when to summarize routes. It will not surprise any CCNA or CCNP certification candidate that OSPF gives us the most options for route summarization, and therefore more details to know! OSPF offers us two options for route summarization configurations. ... more...

Computers » Networks | By Chris Bryant @ Tuesday, 21st March 2006 @ 9:46 PM

When you're studying to pass the CCNA, you're introduced to "private addresses", the address ranges formally referred to as RFC 1918 Private Addresses. (RFC stands for Request For Comment; to see a typical RFC, just put that term in your favorite search engine.) There are three ranges of 1918 Private Addresses, one in each major network class. Class A: 10.0.0.0 /8 Class B: 172.16.0.0 /12 Class C: 192.168.0.0 /16 Be ca... more...