Sunday, May 27, 2012

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!

Thursday, January 12, 2012

Dreams made reality

Okay, so I'm well overdue for a check-in. A lot has happened since my last post so I'll try to fill in the gaps.

First, I got a new job. In my dream field, networking. I'm now an enterprise WAN data technician working in a NOC!

Tomorrow will be my last day of nearly 2 months of training (I was hired in the 3rd week of November). I was initially trained in Facilities, which gave me some background in telephony and TDM circuits (T1, T3, etc). I'm now able to test T1s for errors, troubleshoot phone issues on PRIs and CAS lines, and refer tickets on the local loop out to carriers for resolution.

During my training in Facilities, the company transitioned to ownership by another carrier, and I believe I was likely the last employee hired under the original company. I even played a game of Foosball with the Fortune 1000 CEO on the evening of the last day he owned the company, losing by a few points, undoubtedly due to the few pints of lager I'd had by that point. :p

After about 5 weeks came the good stuff: data training. I was trained on QoS, MPLS (multilinks), VLANs and Trunking, Metro Ethernet, Multilink Frame Relay, BGP, ACLs, subnetting and more. I already have a decent understanding of the LAN side of networking so some of the stuff like Metro E was pretty easy to understand, and I already knew subnetting, ACLs and VLANs pretty well.

On top of everything I've learned, I'm also looking at a reasonable bump in pay as well, which has me preparing a proposal to Lynn as well as a reasonable likelihood of owning a house in my future, especially as my family has one that they're willing to sell me (in one of the best neighborhoods and school districts in the country!)

I've also been offered a job writing articles on smartphones for a tech blog startup, and while I've written a few articles (and will not disclose the website here just yet), I've been so busy with my new job and the holidays that I've not written enough to earn any pay.

Lastly, I also won the Christmas Grand Prize over at's 25-Days-Of-Tegra giveaway! I won a Transformer Prime tablet with keyboard dock, a Sonos sound system, and a Kindle Fire! The stuff hasn't come yet (and has been a daily reminder of how impatient I am) but I'm very excited to see it come. It's possible the Transformer Prime has been delayed by ASUS' announcement that they're releasing a second-edition model that will resolve some of the issues people have had with GPS and WiFi performance due to the metal back of the tablet.

In closing, I'll try to keep up on my blog, maybe post a few Cisco-oriented articles, but I expect my life is going to continue in high gear for the next several months while I continue to focus on learning everything I can about WAN networking, get a ring for my girlfriend, and work on buying the house.

After years of struggle, I'm finally seeing my goals achieved... and I couldn't be happier!