In one of our discussions, Stretch provided an excellent graph illustrating that the ISP competition seems to reduce prices almost linearly and asked me in a later comment to justify the inverse relation between subscription charges and consumer choice.

You might consider this debate to be purely between Stretch and myself, but it’s an interesting example of what you might need to do in daily your job. If you want to be a great networking engineer, you have to be prepared to question everything, including common wisdoms, “well-known truths”, “common practices” and facts that look too good to be true. Ready? Let’s go …

I'm looking for details on how Netflix streams videos over the Internet. I've found their description of encoding and bit rates, but was not able to find lower-layer details (I can only assume they use UDP, but I would like to verify that with someone who's actually using the service).

I would also appreciate any information on whether they work with Service Providers (for example, using local direct peering) to ensure the upstream Internet connections are not clogged with streamed video.

Every so often, someone asks me what tools I use to draw the diagrams. Years ago I was perfectly happy with Visio, but since Microsoft bought it, it became so bloated that I’ve been forced to drop it (it would take minutes to start on my laptop) and revert back to PowerPoint.

Cisco provides great icon libraries (including the visionary “space router” icon shown on the right) in Visio and PowerPoint format and I’m lucky enough to have an older version where the colors of the devices are not light blue but a darker shade of blue/green/gray. Drawing connections between the devices is obviously easier in Visio than in PowerPoint, but if you keep the diagrams simple, you can work around the limitations.

The “All-I-can-eat-mentality” article has triggered (as expected) numerous responses. Some of them provided useful data, links to more information or informative perspectives – many thanks to those readers. A few others were unfortunately following the “I-am-right” line without considering facts. Most of the readers from the Service Provider community decided to stay anonymous (when you read all the comments, it becomes obvious they made a wise decision) or respond off-line.

Whatever your position in this issue, I would like to ask you to keep your comments focused on the topic. Although you were all infinitely more polite than the usual forum/blog crowd and provided some really good arguments, writing angry replies does not help. What’s happening with Internet is (like it or not) our common problem … or you could take the blue pill and continue bashing the other side.

I particularly liked the summary of our discussion posted on Slashdot (where someone included the link to my blog):

Whoa, whoa, whoa, that article seems to be promoting a balanced viewpoint that denies a) that telcos are totally evil and b) that we should all be allowed to have as much bandwidth as we want and not have to pay for it. We'll have none of that nonsense on /.

Red Pineapple was kind enough to share his 15-year-old ATM slides. They include interesting claims like:

ATM has the potential to displace all existing internetworking technologies

One single network handles all traffic types: Bursty data and Time-sensitive continuous traffic (voice/video).

All these claims are still true if you just replace »ATM« with »IP«. So what went wrong with ATM (and why did the underdog IP win)? I can see the following major issues:

Two days ago I’ve managed to write aGenuineStupidity™ (OK, maybe I cannot get a trademark on this concept): the MQC shaping actions cannot be attached to a Dialer interface; they have to be specified on the underlying physical interface (in case of PPPoE link, the outside Ethernet interface).

The reason for my stupidity (apart from the obvious one: writing without testing) is the difference between true logical interfaces and dialer templates. A tunnel interface or a VLAN interface is a true logical interface; it behaves like any other interface (with a few exceptions; for example, tunnel interface does not have an output queue) and you can use most QoS actions (including shaping) on it. A dialer interface is even more “conceptual”. It can never be operational on its own – as soon as the link is established, it’s bound to a physical (for example, BRI0:1) or virtual access interface (which is yet again bound to a physical interface) and the shaping is performed on the final physical interface.

Based on the ADSL reference model, let’s try to figure out how you can influence the quality of service over your ADSL link (for example, you’d like to prioritize VoIP packets over web download). To understand the QoS issues, we need to analyze the congestion points; these are the points where a queue might form when the network is overloaded and where you can reorder the packets to give some applications a preferential treatment.

Remember: QoS is always a zero-sum game. If you prioritize some applications, you’re automatically penalizing all others.

Shahid wrote me an e-mail asking about local command authorization. He would like to perform it within the AAA model, but while AAA local authorization works, it only allows you to specify user privilege level (and autocommand), not individual commands (like you can do on a TACACS+ server).

The Cisco Subnet RSS feed I’m receiving from Network World contained interesting information a few days ago: Cisco has reissued the HTTP security advisory from 2005. The 2005 bug was “trivial”: they forgot to quote the “<” character in the output HTML stream as “&lt;” and you could thus insert HTML code into the router’s output by sending pings to the router and inspecting the buffers with show buffers assigned dump (I found the original proof-of-concept exploit on the Wayback Machine). However, I’ve checked the behavior on 12.4(15)T1 and all dangerous characters (“<” and quotes) were properly quoted. So, I’m left with two explanations.

We all know that the global BGP table is exploding (see the Active BGP entries graph) and that it will eventually reach a point where the router manufacturers will not be able to cope with it via constant memory/ASIC upgrades (Note: a layer-3 switch is just a fancy marketing name for a router). The engineering community is struggling with new protocol ideas (for example, LISP) that would reduce the burden on the core Internet routers, but did you know that we could reduce the overall BGP/FIB memory consumption by over 35% (rolling back the clock by two and a half years) if only the Internet Service Providers would get their act together.