Networks Articles

Computers » Networks | By Chris Bryant @ Tuesday, 25th April 2006 @ 9:03 AM

The most common method of configuring ISDN is with dialer maps, but dial information can also be configured on a logical interface. To pass the CCNA exam, you must know how to configure and troubleshoot both dialer maps and dialer profiles. Dialer Profiles allow different dialing information to be configured onto logical interfaces. The logical interfaces may have different dialing destinations, different remote router names, etc., but they’ll be using the same physical interface.<... more...

Computers » Networks | By Chris Bryant @ Tuesday, 25th April 2006 @ 8:57 AM

To pass the CCNP exams, you’ve got to master Quality of Service, and the first step in doing so is knowing the differences between the different QoS types. Now this being Cisco, we can't just have one kind of QoS! We've got best-effort delivery, Integrated Services, and Differentiated Services. Let's take a quick look at all three. Best-effort is just what it sounds like - routers and switches making their "best effort" to deliver data. This is considered Qo... more...

Computers » Networks | By Chris Bryant @ Monday, 24th April 2006 @ 9:55 AM

To pass the BSCI exam, you need to know the difference between IRDP and HSRP. While they have the same basic function, the operation and configuration of each are totally different. The aim of both is to allow hosts to quickly discover a standby router when the primary router fails. IRDP is commonly used by Windows DHCP clients and several Unix variations, but you do see it in Cisco routers as well. IRDP is defined in RFC 1256. IRDP routers will multicast Hello messages that host d... more...

Computers » Networks | By Chris Bryant @ Monday, 24th April 2006 @ 9:55 AM

QoS - Quality of Service - is a huge topic on both the BCMSN exam and real-world networks. QoS is so big today that Cisco's created separate specialist certifications that cover nothing but QoS! It can be an overwhelming topic at first, but master the fundamentals and you're on your way to exam and job success. If you work with QoS at any level - and sooner or later, you will - you've got to know how to write and apply QoS policies. Creating and applying such a poli... more...

Computers » Networks | By Chris Bryant @ Monday, 24th April 2006 @ 8:55 AM

Passing the CCNA is tough, and one of the toughest parts is keeping all the acronyms straight! Frame Relay has plenty of those, and today we're going to examine what DLCIs do and how they're mapped on a Cisco router. Frame Relay VCs use Data-Link Connection Identifiers (DLCI - pronounced "del-see") as their addresses. Unlike other Cisco technologies, VCs have only a single DLCI in their header. They do not have a source and destination. DLCIs have local signif... more...

Computers » Networks | By Chris Bryant @ Thursday, 20th April 2006 @ 10:42 AM

To be truly prepared for your CCNA and CCNP exams, you need real hands-on experience with real Cisco routers and switches. However, a production network is a really bad place to practice your configurations, but an excellent way to get fired and/or sued. The key to becoming a true CCNA and CCNP is assembling your own Cisco home lab. You don't have to spend a lot of money to do so; used Cisco equipment is cheaper than ever. It's robust as well - I've bought literally hun... more...

Computers » Networks | By Chris Bryant @ Thursday, 20th April 2006 @ 9:24 AM

QoS is a big topic on your BCMSN and CCNP exams, and for good reason. As more and more traffic flows through today's networks, accurately applying QoS to both your routers and switches becomes more important. Note the phrase "accurately applying". You must have a plan in place before you start configuring QoS on your switches, and to create such a plan you should use Cisco's Three-layer Hierarchical Model. This model breaks switches down into three main groups -... more...

Computers » Networks | By Chris Bryant @ Thursday, 20th April 2006 @ 9:18 AM

While routers accept and generate broadcasts, they do not forward them. This can be quite a problem when a broadcast needs to get to a device such as a DHCP or TFTP server that's on one side of a router with other subnets on the other side. If a PC attempts to locate a DNS server with a broadcast, the broadcast will be stopped by the router and will never get to the DNS server. By configuring the ip helper-address command on the router, UDP broadcasts such as this will be tran... more...

Computers » Networks | By Chris Bryant @ Tuesday, 18th April 2006 @ 12:17 PM

CCNA exam success depends partially on knowing the details of ISDN, and there are plenty of them! To help you review for your CCNA exam, here are a few ISDN details that you must know on exam day. (They help in the real world, too – and there are still plenty of ISDN networks out there! The Cisco-proprietary version of HDLC is the default encapsulation type for serial and ISDN interfaces. R2#show interface serial0 Serial0 is up, line protocol is up Hardware is HD64... more...

Computers » Networks | By Chris Bryant @ Tuesday, 18th April 2006 @ 12:07 PM

I know from experience that part of the excitement and anxiety of putting together your own CCNA / CCNP home lab is deciding what to buy! While you can make a workable home lab out of almost any combination of Cisco routers and switches, some routers are better suited for home lab work than others because they can fill multiple roles. When you buy CCNA or CCNP "lab kits" - bundles of routers and switches - you can get a little confused about whether you're getting a good deal... more...

Computers » Networks | By Chris Bryant @ Tuesday, 18th April 2006 @ 12:03 PM

If a Layer Two switch doesn't have the capabilities to run IGMP Snooping, it will be able to run CGMP - Cisco Group Membership Protocol. CGMP allows the multicast router to work with the Layer Two switch to eliminate unnecessary multicast forwarding. CGMP will be enabled on both the multicast router and the switch, but the router's going to do all the work. The router will be sending Join and Leave messages to the switch as needed. PIM must be running on the router interfac... more...

Computers » Networks | By Chris Bryant @ Monday, 17th April 2006 @ 8:57 AM

Multicasting is a vital topic on your BCMSN, CCNP, and CCIE exams, and it can also be very confusing when you first start studying it. Multicasting uses concepts that are unlike anything you've run into in your routing protocol studies, and that can throw you at first. I speak from experience that multicasting is like any other Cisco technology - learn the basics, master the fundamentals, and then build your skills on that foundation. One such fundamental is the RPF Check, or Re... more...

Computers » Networks | By Chris Bryant @ Monday, 17th April 2006 @ 8:56 AM

To pass the CCNA exam, you've got to know how to work with IGRP and EIGRP unequal-cost load balancing. You may not see much IGRP in production networks anymore, but you'll see a lot of EIGRP, and part of fine-tuning your EIGRP network is making sure that all paths are in use while allowing for varying bandwidth rates. Using the variance command is the easy part - it's getting the metric that's the hard part with IGRP. With EIGRP, you just look in the topology table and... more...

Computers » Networks | By Chris Bryant @ Thursday, 13th April 2006 @ 1:56 PM

OSPF route redistribution is an important topic on the BSCI exam, and it's a topic full of details and defaults that you need to know for the exam room and the job. To help you pass the BSCI exam, here's a quick review of some of the OSPF route redistribution basics. To see if a router is an ABR or ASBR, run show ip ospf. This also displays any routes being redistributed into OSPF on this router. R1#show ip ospf Routing Process "ospf 1" with ID 1.1.1.1 <... more...

Computers » Networks | By Chris Bryant @ Thursday, 13th April 2006 @ 1:55 PM

Ever since you picked up your first CCNA book, you've heard about multicasting, gotten a fair idea of what it is, and you've memorized a couple of reserved multicasting addresses. Now as you prepare to pass the BCMSN exam and become a CCNP, you've got to take that knowledge to the next level and gain a true understanding of multicasting. Those of you with an eye on the CCIE will truly have to become multicasting experts! Having said that, we're going to briefly review... more...

Computers » Networks | By Chris Bryant @ Thursday, 13th April 2006 @ 1:13 PM

RIP isn't exactly the most complex routing protocol on the CCNA exam, but that makes it easy to overlook some of the important details you must keep in mind in order to pass the exam! To help you review for the exam, here are just a few of those details! RIP’s default behavior is to send version 1 updates, but to accept both version 1 and 2 routing updates. R2(config)#router rip R2(config-router)#net 172.16.0.0 R2(config-router)#^Z R2#show ip protocolsmore...

Computers » Networks | By Chris Bryant @ Wednesday, 12th April 2006 @ 7:56 AM

In this section, you're going to be reintroduced to a networking model you first saw in your CCNA studies. No, it's not the OSI model or the TCP/IP model - it's the Cisco Three-Layer Hierarchical Model. Let's face it, just about all you had to do for the CCNA was memorize the three layers and the order they were found in that model, but the stakes are raised here in your CCNP studies. You need to know what each layer does, and what each layer should not be doing. This is ... more...

Computers » Networks | By Chris Bryant @ Wednesday, 12th April 2006 @ 7:56 AM

For CCNA exam success, you had better know what split horizon is, how to turn it off, and when to turn it off. Knowing when to turn split horizon off is also important in production networks, because it can cause a hub-and-spoke network to have incomplete routing tables on the spokes. Split horizon exists for a very good reason - routing loop prevention. The rule of split horizon states that a router cannot send an advertisement for a route out the same interface that it came in on. Sp... more...

Computers » Networks | By Chris Bryant @ Wednesday, 12th April 2006 @ 7:55 AM

To pass the BSCI exam and become a CCNP, you have to be aware of the proper use of passive interfaces. You learned about passive interfaces in your CCNA studies, but here we’ll review the basic concept and clear up one misconception regarding passive interfaces and OSPF. Configuring an interface as passive will still allow the interface to receive routing updates, but the interface will no longer transmit them. While the command itself would make you think this command will be applied a... more...

Computers » Networks | By Chris Bryant @ Saturday, 8th April 2006 @ 9:57 AM

OSPF is a major topic on your CCNA exam, as well it should be. OSPF is a widely-used WAN protocol, and you need to learn the fundamentals before moving on to more complicated configurations. One such detail is the OSPF Router ID, or RID. The RID is the dotted decimal value by which other OSPF routers will identify a given OSPF router. There are some interesting defaults for this value, and a command you should know to hardcode the RID. You had also better know what has to happen for this ... more...