It’s probably time for a post about questions that are often asked on fora, discussion groups and me personally about networking. Here is some general advice to aid in networking for anyone interested in the technology or pursuing a certification (Comptia Network+, CCENT, CCNA).

I’ve completed CCNA. What should I choose now: Voice, Security, …?
An often asked question on fora, but I don’t get why. If you’re interested in something, go for it. If you’re interested in money only, it doesn’t matter what you choose, as all these jobs have similar pay.  If you honestly can’t choose because of the broad interest (as me), go for CCNP if you feel up to the task. Or choose something you know will benefit you at your current or future job. Nice indicators are the used materials: if your work has IP Phones, CCNA Voice may be an interesting option. If they have a wireless deployment, consider CCNA Wireless. If they care about security (and they usually do), CCNA Security can help. If they use Junipers, consider a Juniper certificate, because that’s a known certification too.

Why do you need IP addresses if MAC addresses are already unique? Why not use them?
A surprisingly often asked question. Granted this is a silly question from the perspective of a network engineer but I can understand it’s not clear to someone without experience in the field of networking.
MAC addresses are unique, but not logical. It would be impossible for every router to keep track of all MAC addresses on the planet, and keep updating their location. That would be well over 5-6 billion entries at this point, if not double. By comparison, a modern ISP core router has a route table pointing to networks, not individual devices. With over 350,000 routes in a BGP routing table these days, that’s still impressive and very demanding of a router, but not impossible.

I’ve for an urgent problem with Packet Tracer
Stop. Right. There. There’s no such thing as Packet Tracer and urgent. I’m just mentioning it because it’s not fun if someone mails you saying it’s urgent, you try to help out a little, and in the end it’s a simulation, which is unreliable and not urgent. I’m happy to help out but priorities are important, of course. Which brings me to the next question:

Why does command not work in Packet Tracer?
Because it’s a simulation program, and only contains the commands necessary for CCNA. It’s a great program to learn about networking, and I’ll even go as far as saying that you can get a CCNA certificate by practicing using only this software and no real equipment, but keep in mind it’s not the real equipment, and there are differences. If something doesn’t work as expected (especially layer 2 stuff), it might work fine on real hardware.

I’m studying for CCNP. How do I simulate/emulate switches?
Unfortunately you can’t. I see this question at least once a week somewhere. Packet Tracer only supports basic PVST+ and VTP, and trunking. GNS3 cannot emulate the ASICs used by Catalyst switches properly. With the NM-16ESW module you can do basic Spanning-Tree and I’ve even heard of people getting VTP running, but that’s about it. I’ve never tried other simulators/emulators (Boson, IOU)  but people have reported to me that there was no improvement in the layer 2 stuff. So for switching, you’ll need a real switch. My personal recommendation for the smallest budget is a Cisco 3550, that will get you a long way towards the exam.

Is fiber faster than Ethernet, and does cable length influence latency?
Data over fiber travels at light speed, over Ethernet it’s a bit slower. But bandwidth is the same: a 1Gbps fiber can do 1Gbps, just like a 1Gbps UTP. Also, theoretically cable length does have an influence, but don’t expect any noticeable results until hundreds of kilometers are involved. Data will traverse a full 100m UTP cable run in about 0,5 microseconds.

My wireless doesn’t work/is unstable/is slow. Why?
Wireless is a nice technology, but realise the limits. I’ve heard stories of people trying to connect +100 devices on one access point, or distances of over 50 meters, not counting any concrete walls, and so on. Wireless works, but try to keep it as a last resort, or at least favor the conditions so it doesn’t suffer from noise and other factors. I will explain more in an upcoming blog post.

Can I make my internet go faster?
Yes and no. Keep in mind, as with most things, that there are physical limits. If you have a 1Mbps line from your ISP, nothing is going to make a 20Mbit line out of it.
Things that may help for some applications are a proxy and a DNS caching server. I’ve heard people using pfSense as a proxy server in their network. I noticed my ISP performs poor on DNS sometimes, so another external DNS, or a DNS caching server can help. But both of these mostly increase response time when browsing. Apart from that, there’s no added benefit when streaming media.

My home network is slow, what is causing it?
It can be many things. If you’re using wireless, see the question about wireless above. It depends on the stress each device receives. As a general rule of thumb, if you’re using five devices or more on a regular basis for more intensive traffic patterns (streaming video and the like), consider using a separate small SOHO switch instead of connecting everything to a router. The router will most likely have to handle a lot already. Even a cheap DES-1008D can do wonders, as it takes the load off the router. Considering upgrading everything to gigabit can help too.
Something else that can slow the network are poor cabling or a device causing excessive broadcasts (malware). In the end, the only way to find out, is doing tests, run Wireshark, and try to locate the bottleneck.

I followed lessons and now I’ve waited six months for my exam and
WHY? If I waited six months after my lessons, I would never have passed. Not even at the second try. My last bit of advice for today: if you’ve taken lessons and/or studied for it, go for it. Do not wait. I have yet to meet someone who waited and didn’t regret that. If it’s fresh in your mind, it’s best. You can do it!