Networks Articles

Computers » Networks | By Chris Bryant @ Monday, 17th July 2006 @ 12:57 PM

As a CCNA or CCNP, one thing you've got to get used to is that change is constant. Cisco regularly issues new IOS versions, not to mention the many different kinds of hardware they produce! While it's always nice to have "the latest and the greatest" when it comes to routers, switches, firewalls, etc., we have to be prepared for the fact that not all our clients are going to have that latest and greatest! For instance, there are still quite a few Catalyst 5000 switches ... more...

Computers » Networks | By Chris Bryant @ Friday, 14th July 2006 @ 2:03 PM

When you're studying to pass the Cisco CCNA and CCNP certification exams, you quickly learn that there's always something else to learn. (You'll really pick up on this in your CCIE studies, trust me!) Today we'll take a look at an often-overlooked topic in Frame Relay, the encapsulation type. You don't exactly change this on a daily basis in production networks (not if you want to stay employed, anyway!), but it's an important exam topic that you must be familiar... more...

Computers » Networks | By Chris Bryant @ Friday, 14th July 2006 @ 8:41 AM

BECNs and FECNs aren't just important to know for your Cisco CCNA and CCNP certification exams - they're an important part of detecting congestion on a Frame Relay network and allowing the network to dynamically adjust its transmission rate when congestion is encountered. The Forward Explicit Congestion Notification (FECN, pronounced "feckon") bit is set to zero by default, and will be set to 1 if congestion was experienced by the frame in the direction in which the fram... more...

Computers » Networks | By Chris Bryant @ Wednesday, 12th July 2006 @ 2:07 PM

To earn your Cisco CCNA and CCNP certifications, you've got to master ISDN - and despite what some people say, there's still a lot of ISDN out there that needs to be supported. And when it comes to troubleshooting ISDN, there's a lot to look at. Is the correct ISDN switchtype configured? Are the dialer map statements correct? What about the dialer-group and dialer-list commands? And that's just the start. I always say that all troubleshooting starts at Layer 1, the... more...

Computers » Networks | By Chris Bryant @ Tuesday, 11th July 2006 @ 9:56 AM

To pass the Cisco CCNA and CCNP certification exams, as well as becoming a world-class networker, you've got to know how and when to use floating static routes. And if you're wondering what makes them "float" -- read on! In this example, R1 and R2 are running OSPF over a Frame Relay network, 172.12.123.0 /24. They're also connected by a BRI ISDN link, 172.12.12.0 /24. R1 is advertising a loopback network, 1.1.1.1 /32, via OSPF. We want R2 to have a route to that loo... more...

Computers » Networks | By Chris Bryant @ Monday, 10th July 2006 @ 6:48 PM

You may run into situations where a router in a remote location needs to dial in to a central router, but the toll charges are much higher if the remote router makes the call. This scenario is perfect for PPP Callback, where the callback client places a call to a callback server, authentication takes place, and the server then hangs up on the client! This ensures that the client isn't charged for the call. The server then calls the client back. In the following example, R2 has... more...

Computers » Networks | By Susan Jan @ Thursday, 29th June 2006 @ 5:24 AM

A computer network is a collection of two or more computers with communication between them through a medium. The communication medium can be through radio waves, wires, infrared, optical fibers etc. Computer network is an integral part of our daily lives, with the most important reason being that of communication. The use of computer networking is to share resources like fax machines, printers, modems, files etc., and its other uses are database server, computer server, email, chat, inte... more...

Computers » Networks | By Chris Bryant @ Tuesday, 13th June 2006 @ 7:56 AM

Dialer Watch is a vital part of your CCNA and CCNP studies, particularly for the BCRAN exam, but it's one of the most misunderstood technologies as well. To help you pass the CCNA and CCNP certification exams, here's a detailed look at Dialer Watch. Dialer Watch allows you to configure a route or routes as "watched" when the watched route leaves the routing table and there is no other valid route to that specific destination, the ISDN link will come up. In the following ... more...

Computers » Networks | By Chris Bryant @ Friday, 9th June 2006 @ 7:58 AM

One of the first things you learned about Frame is that the LMI also serves as a keepalive, or a heartbeat - and if three consecutive LMIs are missed, the line protocol goes down. There's a limitation to LMI as a keepalive, though. The LMI is exchanged only between the DTE and the closest DCE. The LMI is therefore a local keepalive that does not reflect any possible issues on the remote end of the virtual circuit. Taking the LMI concept to the next logical level, Frame Relay End-... more...

Computers » Networks | By Christine Harrell @ Thursday, 25th May 2006 @ 3:18 PM

Most businesses have laws and regulations for how long specific data must be stored, but still many companies don’t have a tape drive, tape libraries, secondary storage or any plan for archiving data. Even if your industry doesn’t have specific requirements, keeping a well documented business information library is a safe bet. Recently, the residential building company Urban Renaissance Agency realized that it had lost archived building plan data for 555 (31%) of its condos due to “insufficien... more...

Computers » Networks | By Chris Bryant @ Thursday, 18th May 2006 @ 1:38 PM

EIGRP is a major subject of the CCNA exam, and Cisco goes into even more detail with EIGRP on your CCNP exams. Part of that detail is the purpose and configuration of EIGRP stub routers. A problem with EIGRP comes in when a successor is lost and there is no feasible successor. DUAL doesn't give up that easily, though. DUAL will mark the route as Active, indicating that the route is being calculated and cannot be used to route data, and will send out a Query message. ... more...

Computers » Networks | By Chris Bryant @ Thursday, 18th May 2006 @ 1:30 PM

To pass your CCNA exam and earn this coveted certification, you must understand the details of port-based authentication. This knowledge has a great deal of value in production networks as well, since this authentication scheme is regularly implemented. Let's take a look at this particular CCNA skill. Consider a situation where you have a server that will be connected to your switch, and you want the port to shut down if a device with a different MAC address that that of the switch... more...

Computers » Networks | By Chris Bryant @ Tuesday, 16th May 2006 @ 8:56 AM

To earn your Cisco CCNA certification and pass the BSCI CCNP exam, you have to know your protocol basics like the back of your hand! To help you review these important concepts, here's a quick look at the basics of RIPv1, RIPv2, IGRP, and EIGRP. RIPv1: Broadcasts updates every 30 seconds to the address 255.255.255.255. RIPv1 is a classful protocol, and it does not recognize VLSM, nor does it carry subnet masking information in its routing updates. Update contains entire RIP routi... more...

Computers » Networks | By Chris Bryant @ Tuesday, 16th May 2006 @ 8:55 AM

ISDN is a huge topic on both your Cisco CCNA and BCRAN CCNP exams. While many ISDN topics seem straightforward, it’s the details that make the difference in the exam room and working with ISDN in production networks. Configuring and troubleshooting multilink PPP is just one of the skills you’ll need to pass both of these demanding exams. With BRI, we've got two B-channels to carry data, and both of them have a 64-kbps capacity. You might think it would be a good idea to have both ... more...

Computers » Networks | By Chris Bryant @ Thursday, 11th May 2006 @ 9:55 AM

To earn your CCNA or CCNP certification, you've got to understand the basics of trunking. This isn't just a CCNA topic - you must have an advanced understanding of trunking and etherchannels to pass the BCMSN exam and earn your CCNP as well. Before we address those advanced topics, though, you need to master the fundamentals! A trunk allows inter-VLAN traffic to flow between directly connected switches. By default, a trunk port is a member of all VLANs, so traffic for any and... more...

Computers » Networks | By Chris Bryant @ Thursday, 11th May 2006 @ 9:55 AM

Earning your CCNP certification and passing the BSCI exam depends on knowing the details of many Cisco technologies, ISIS chief among them. To help you prepare for exam success, here's a list of ISIS terminology and basic concepts that will help you pass this tough exam. Enjoy! ISIS Terms: Domain: section of the network under common administrative control Area: logical segment of the network composed of contiguous routers and their data links Intermediate System:... more...

Computers » Networks | By Chris Bryant @ Thursday, 11th May 2006 @ 9:02 AM

Whether you're on the road to the CCNA, CCNP, MCSE, or you're on any other computer certification track, the odds are that sooner or later, you're going to fail an exam. It's happened to almost all of us, yours truly included. What you have to keep in mind in these times is that success is not a straight line. You've probably seen charts showing the growth of an industry or a business -- you know, the ones that go from left to right, and look kind of jagged. The lin... more...

Computers » Networks | By Chris Bryant @ Tuesday, 9th May 2006 @ 2:51 PM

Like TCP, BGP is connection-oriented. An underlying connection between two BGP speakers is established before any routing information is exchanged. This connection takes place on TCP port 179. As with EIGRP and OSPF, keepalive messages are sent out by the BGP speakers in order to keep this relationship alive. Once the connection is established, the BGP speakers exchange routes and synchronize their tables. After this initial exchange, a BGP speaker will only send further updates upon... more...

Computers » Networks | By Chris Bryant @ Tuesday, 9th May 2006 @ 12:43 PM

When you're working on your BCMSN exam on your way to CCNP certification, you'll read at length about how Cisco routers and multilayer switches can work to provide router redundancy - but there's another helpful service, Server Load Balancing, that does the same for servers. While HSRP, VRRP, and CLBP all represent multiple physical routers to hosts as a single virtual router, SLB represents multiple physical servers to hosts as a single virtual server. In the following exa... more...

Computers » Networks | By Chris Bryant @ Tuesday, 9th May 2006 @ 12:11 PM

Imagine this. You have an appointment with a client to work on a server or router install. A few minutes before you're scheduled to be there, you decide there's something really good on TV you'd like to watch. Or you decide to go to the gym, or play a game, or do anything else except go see the client. Even if you weren't going to get fired for not showing up, it's certainly unfair to the client. You've got a professional obligation, and you should be ... more...