Tech-Seeker

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 hundreds of used routers and switches over the years and have had very few problems. I owe much of my skill to practicing configurations and troubleshooting in my own home lab.

2501 routers are fantastic for CCNA and CCNP home labs. They come with two serial interfaces, allowing you to connect one interface directly to another router (you’ll need a DTE/DCE cable for that, too) while connecting another to a frame relay switch if you like. If you don’t have a frame relay switch, you can connect a 2501 directly to two other routers via the serial interfaces.

You also have an AUI port, which requires a transceiver to operate as your Ethernet interface. Transceivers are pretty cheap and readily available from Cisco resellers and ebay vendors, so pick one up for each 2503 you decide to buy.

2501 routers don’t come with BRI interfaces, but not every router in your lab has to be ISDN-ready. If you choose not to have ISDN in your lab at all, 2501s are the way to go. If you do want to run ISDN and have an ISDN simulator device, you can get two 2503s and the rest of your routers can be 2501.

All in all, 2501 routers are great for your CCNA / CCNP home lab. They cost less than $100 each on ebay, so they’re also very affordable. There’s no better training than training on your own CCNA or CCNP home lab, and you can always sell the equipment later if you like. Basically, you’re renting the routers and switches, and the experience you get by working with the real deal is invaluable.

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 command to take effect, so let’s take a more detailed look at the OSPF RID.

In this example, R1 has an adjacency with R2 and R3 over the 172.12.123.0/24 frame network. R1 is the hub, with R2 and R3 as the spokes. No other interfaces are OSPF-enabled on any of the routers. Running show ip ospf neighbor on R1, we see some unusual values under “Neighbor ID”, which is another name for the OSPF RID.

R1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface

3.3.3.3 0 FULL/DROTHER 00:01:57 172.12.123.3 Serial0

2.2.2.2 0 FULL/DROTHER 00:01:57 172.12.123.2 Serial0

Notice the Neighbor ID of each remote address is the loopback address. How can that be if they’re not OSPF-enabled?

When determining the Router ID (RID) of an OSPF-enabled router, OSPF will always use the numerically highest IP address on the router’s loopback interfaces, regardless of whether that loopback is OSPF-enabled.

What if there is no loopback? OSPF will then use the numerically highest IP address of the physical interfaces, regardless of whether that interface is OSPF-enabled.

BOTTOM LINE: An interface does not have to be running OSPF to have its IP address used as the OSPF RID.

The OSPF RID can be changed, but it requires a restart or to reinitialize the OSPF routing process. Use the router-id command to change the default RID of each router as shown, and clear the OSPF process to do so.

R1#conf t

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

R1(config)#router ospf 1

R1(config-router)#router-id 11.11.11.11

Reload or use “clear ip ospf process” command, for this to take effect

R1#clear ip ospf process

Reset ALL OSPF processes? [no]: yes

1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

1d05h: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial0 from 2WAY to
DOWN, Neighbor Down: Interface down or detached

After entering the router-id command, the router console informed you that you have to reload the router or reset the OSPF processes for this to take effect. You enter the clear ip ospf process command to do this. Notice that when you’re asked if you really want to do this, the prompt is “no”? That’s because all the OSPF adjacencies on this router will be lost and will have to begin the process again. That’s OK on a practice rack, not good in a production network. Don’t use that one at work.

The OSPF RID is not a complicated concept, but the fact that an interface doesn’t have to be OSPF-enabled in order to have its IP address act as the RID takes some getting used to. And remember – when the router or switch asks you a question and the prompted answer is “no”, take one step back and make sure you really want to do what you’re about to do!

I’ve been active in the Cisco Certification track for four years, working my way from the CCNA to the coveted Cisco Certified Internetwork Expert title, and during that time I’ve conducted job interviews and casual conversations with hundreds of CCNAs and CCNA candidates.

The CCNA is an exciting beginning to your Cisco career, but just having the certification simply isn’t enough. A recruiter or interviewer isn’t going to be impressed just with the cert you’ve got to have some real-world knowledge to back it up.

I’ve been down that road myself, and sat on both sides of the CCNA job interview table. With that in mind, I’d like to offer to you some tips on becoming a truly valuable and employable CCNA.

Get some hands-on experience. I know the trap well. You can’t get experience until you get a CCNA, and you can’t get a CCNA without real experience. Well, actually, you can, but do you want to? Working on simulators is fine to a certain extent, but don’t make the classic mistake of depending on them. I’ve seen plenty of CCNAs who were put in front of a set of routers and really didn’t know what to do or how to put together a simple configuration, and had NO idea how to begin troubleshooting.

There are CCNA classes that offer you the chance to work with industry experts on real Cisco equipment. Beyond that, you can put together your own CCNA rack for less than $1000 by buying used routers. Some people think that’s a lot of money, but this is the foundation of your career. Treat it that way. The work you do now is the most important work you’ll ever do. Do it on real Cisco equipment. The skills I learned as a CCNA helped me all the way up to the CCIE.

Besides, after you get your CCNA (and after that, hopefully you’ll choose to pursue the CCNP), you can always get some of your money back by selling the equipment. The hands-on experience you gain this way is invaluable.

Know binary math. Do NOT go the easy route of memorizing a subnet mask chart for the CCNA exam. I know some people brag about being able to pass the CCNA exam without really understanding binary math. I’ve seen those people on the other side of the interview table, and they’re not laughing when I ask them to do a subnetting question. They’re not laughing when they can’t explain or create a VLSM scheme. That chart does nothing to help you understand what’s going on.

If you can add and know the difference between a one and a zero, you can do binary math. Don’t let the name intimidate you. Become a REAL CCNA — learn binary math !

Run “show” and “debug” commands. No commands help you truly understand how things work in a Cisco network than show and debug commands. As you progress through the Cisco certification ranks, you’ll be glad you started using these at the CCNA level.

Do you need to know these commands for the exam? Probably not. Do you need them to be successul in the real world? Absolutely.

The Cisco certification track has been great to me, and it can boost your career as well, whether you stop at the CCNA, CCNP, or go all the way to the CCIE. It’s the skills you develop today that will truly make you a networking engineer. Don’t take shortcuts or get the attitude of “just passing the exam”.

It’s what you achieve after the exam that counts, and it’s the work you put in before passing the exam that makes those achievements possible.

Good luck !

Chris Bryant, CCIE #12933

Preparing to pass the CCNA exam and earn this important Cisco certification? Route summarization is just one of the many skills you’ll have to master in order to earn your CCNA. Whether it’s RIP version 2, OSPF, or EIGRP, the CCNA exam will demand that you can flawlessly configure route summarization.

Route summarization isn’t just important for the CCNA exam. It’s a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately – what I like to call “concise and complete” routing tables.

The first skill you’ve got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we’ll only illustrate how to convert the first and second octet from decimal to binary.

100 16 = 01100100 00010000

100 17 = 01100100 00010001

100 18 = 01100100 00010010

100 19 = 01100100 00010011

To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren’t used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.

But we’re not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a “1″ for every bit to the left of the line we drew previously, and a “0″ for every bit to the right. That gives us the following string:

11111111 11111100 00000000 00000000

Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.

For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level – it’s not configured under the protocol. On the interface that should advertise the summary route, use the command “ip summary-address”. Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.

R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0

R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0

The main difference between the two is that the EIGRP command must specify the AS number – that’s what the “100″ is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there’s no additional value needed in the configuration.

For OSPF, the commands differ. If you’re configuring inter-area route summarization, use the “area range” command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.

I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions – you either know how to do it or you don’t. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Here’s to your success!

CCNA stands for Cisco Certified Network Associate – a certification for IT professionals that is issued by Cisco Systems, Inc., one of the most successful computer networking companies. Cisco manufactures and markets a wide range of devices for both enterprises and telecommunications carriers. Cisco is an abbreviation of San FranCISCO.

The Cisco Certified Network Associate is an apprentice, or foundation level (along with Cisco Certified Design Associate), within the three levels of certification that include Associate, Professional, and Expert. Basically, CCNA professionals are certified to install, configure, and operate LAN, WAN, and dial access services for small networks (100 nodes or fewer), including but not exclusive to use of these protocols: IP, IGRP, Serial, Frame Relay, IP RIP, VLANs, RIP, Ethernet, and Access Lists. The certification is valid for three years, after which recertification may be sought.

In order to hold a CCNA certification, a candidate has to pass either the Cisco Certified Network Associate Exam or a combination of Introduction to Cisco Networking Technologies Exam and Interconnecting Cisco Networking Devices Exam. Main topics for these three exams include Planning and Designing; Design and Support; Implementation and Operation; Troubleshooting; and Technology. Other related topics may also appear on any specific delivery of the exam.

There are also some recommended training programs that may be taken before the above-mentioned examinations. These programs include Introduction to Cisco Networking Technologies (INTRO), Interconnecting Cisco Network Devices (ICND), and Additional Training (CCNA Prep Center Pilot). These trainings incorporate topics such as fundamental knowledge and comprehension of networking; how to select, connect, configure, and troubleshoot the various Cisco networking devices; sample questions, simulations, e-learning modules, labs, tips, etc.