Configuring QoS in Cisco IOS

I'm back! Today I'm posting a how-to on QoS (Quality of Service) configuration on Cisco routers and switches.

QoS is a valuable tool whenever you have different types of traffic arriving at a router where they'll need to be aggregated and sent out over a single link like a WAN connection. Some types of data and applications require traffic to be handled with as little latency and jitter as possible; VOIP is a prime example of this, as well as Citrix, RDP, and anything else that involves streaming audio and video.

The reason this is important is because as a traffic arrives in a router, it gets sent into a processing queue in the router based upon the order in which the packet was received. After routing decisions are made, this traffic is sent into an input queue for the WAN interface in preparation of being sent out over the WAN link.

Traffic passes from this input queue into the transmit ring, a hardware output queue. If this queue fills up during a period of high traffic congestion, additional traffic arriving to the interface is queued in the software output queue, where it waits on room in the transmit ring to become available. If the software output queue (usually just called the output queue) gets filled up and traffic is still arriving at the interface, the interface has to start dropping packets. These are recorded as "Output drops" when you do a show interface command.

If this happens, critical data can be dropped, or voice traffic can be delayed while it sits in the output queue with less important traffic in front of it. Even if the voice traffic is successfully delivered, the delays can cause stuttering and poor quality on the call.

QoS prevents problems like these by guaranteeing bandwidth to critical data and preventing that traffic from being dropped if the circuit becomes congested. It can also be configured to prioritize certain types of traffic over others in terms of the order they are transmitted, to ensure time-sensitive traffic is transmitted as quickly as possible.

Hit the jump and we'll look at this in detail!

Fun with Tasker Part II: Covert mugshots!

Okay Blog, I've been neglecting you. Today, I'll outline a neat little trick once again using the amazing automation tool, Tasker.

First, I've an admission to make. My phone doesn't use one of those coded lockscreens. There's a couple reasons for this... I don't have time to deal with it, and it's far too easy to get around those screens by looking at a screen at a shallow angle and seeing where the fingerprints are.

That said, my phone hardly is lacking in the security department. I've written a few pretty involved scripts in Tasker that will, when I text the phone a secret phrase, turn my phone into an information-gathering powerhouse.

Specifically in this post I'm going to describe how I can covertly and remotely grab photos from the front and rear cameras on my phone as well as see the ugly mug of the last person who unlocked my screen, and have those photos quietly emailed to me. This can be an awesome tool if your phone is stolen or if you just want to know who the last person to unlock your screen was.

Let's get started!

The Necromancer

The title of this blog post also happens to be the name of the book I'm reading. Perhaps I've just been inspired to do a little necromancy of my own, but with less cadavers and more circuit board.

I'll explain; let's start with the fact that something's been bugging me. My desktop PC does not have a discreet GPU (video card).

You might be thinking, "WTF, and you call yourself an electronics freak?!" Well, you've got me there, but I do have reasons. One primary reason is that I'm not a gamer anymore. I do almost everything on this laptop nowadays, and I only took my desktop out of storage a few weeks ago so that I could get a decent VM box running in the basement next to my HTPC and my Cisco lab hardware.

However, my integrated GPU (despite it being a reasonably beefy AMD HD 3200) just ain't cuttin' it for some of the video processing and RemoteFX stuff I'd like to mess around with.

Fortunately, I have an NVIDIA 8800 GTS in a static bag that should do what I need it to do. Unfortunately, it's going to take a little more than me popping this sucker into my PC to get it running.

Problem #1: The graphics card does not have an enclosure for the heat sink; the fan cannot circulate air to keep it cool.

Problem #2: It's damaged goods. (Okay, I lied, the card isn't entirely dead. But someone who brings sick people back to life is a doctor, and that's a lot less fun than being a Necromancer!) It displays bands of pixels vertically across the screen that are visible during the boot process, which means it's a hardware issue, not a driver problem. Additionally, it usually won't boot into Windows, causing the system to hang when the operating system is starting up. On the rare chance it does make the boot into Windows, graphics are horribly distorted.

So, I'm screwed, right? Hell no! I wouldn't pass up an opportunity like this! Read on to see how I got this old workhorse running again.

Fun with Tasker Part I: Weather-adaptive alarm clock.

One of those things I always dreamed of having was an alarm clock that woke me up early on those mornings where Mother Nature decided to hand me a nice blizzard before work or school to struggle through.

A couple months back I started playing with Tasker, an amazing Android application that you've probably already heard me gush about in previous posts. In short, for about the price of a Value Meal at McDonalds, Tasker allows you to set up triggers on your phone that you can use to carry out a virtually limitless set of actions. And really, that'll pay for itself, because you can set it up to do countless things for you that other applications charge for. I've got a bunch of profiles I've set up and I'll be sharing them here on my blog over a period of time.

So I'll cut to the chase. I used Tasker to create a weather-adaptive alarm clock, and posted the profile on Tasker's Wiki page, so feel free to try it out!
http://tasker.wikidot.com/weather-clock

How To: Manage an Active Directory directly from a remote PC.

The Active Directory Users and Computers MMC is commonly used to administer users in an Active Directory via the domain controller. The MMC snap-in is designed to be used by a user that exists on the domain that is being administered; it will determine your rights to make changes to accounts based upon your current login ID.

So let's assume you want to manage an Active Directory on a different domain than the one you are on. Not only do you need to log in as a user on that domain, but you also need to force the snap-in to connect to a seperate domain controller. To do this, you will want to create a .BAT file that employs a runas command. (NOTE: This method can also be used as an additional layer of security so that you can administer the Active Directory from a non-administrative account, avoiding the risks of a trojan or virus gaining access to Active Directory information.) Hit the Read link for details!

How To: Hack a driver to support your hardware

Okay, so for some reason or another you want to install a driver that doesn't officially support your hardware. Maybe it's a (much cooler) driver for a competitor's product, maybe you can't find the driver and you happen to have another driver for a similar device, etc.

So whatever your reasons are, this is possible, though the results can't be guaranteed. Hardware has plenty of differences that require a very specific driver to ensure that it works properly. But if you don't have any other option, read on to find out how to hack support for your hardware into a driver!

How To: Cracking a boot-time Supervisor password on an IBM ThinkPad

I've been doing laptop repair for a while now, and most of what I end up doing is opening a laptop up and cleaning out a heatsink to prevent overheating problems.

I do run into a fair share of problems like DVD drives that won't close, power jacks that have come unsoldered, displays that have been cracked / have daiquiris dumped on them, (there is such a thing as partying too hard), keyboard replacement, etc.

But a few months back I had an interesting request: unlocking an older IBM ThinkPad that had a boot-time supervisor password preventing access.