Category: QoS

Approximately two years ago I tried to figure out whether aggressive marketing of deep buffer data center switches makes sense, recorded a few podcasts on the topic and organized a webinar with JR Rivers.

Not surprisingly, the question keeps popping up, so it seems it’s time for another series of TL&DR articles. Let’s start with the basics:

The last presentation during the Tech Field Day Extra @ Cisco Live Europe event was a Cisco-Apple Partnership presentation, and we expected an hour of corporate marketese.

Can’t tell you how pleasantly surprised we were when Jerome Henry started his very technical presentation explaining the wireless goodies you get when using iOS with IOS.

A while ago I decided it's time to figure out whether it's better to drop or to delay TCP packets, and quickly figured out you get 12 opinions (usually with no real arguments supporting them) if you ask 10 people. Fortunately, I know someone who deals with TCP performance for living, and Juho Snellman was kind enough to agree to record another podcast.

One of my readers watched my TCP, HTTP and SPDY webinar and disagreed with my assertion that shaping sometimes works better than policing.

TL&DR summary: policing = dropping excess packets, shaping = delaying excess packets.

Here’s the picture he sent me (watch the video to get the context and read this article to get the background details):

While some people spread misinformation others work hard to figure out how to make TCP work on exotic links with low bandwidth and one second RTT.

Ulrich Speidel published a highly interesting article on APNIC blog describing the challenges of satellite Internet access and the approach (network coded TCP) they took to avoid them.

When someone tells you that “TCP is a lossy protocol” during a job interview, don’t throw him out immediately – he was just trusting the Internet a bit too much (click to enlarge).

Everyone has a bad hair day, and it really doesn’t matter who published that text… but if you’re publishing technical information, at least try to do no harm.

A. Friend sent me a long list of questions after listening to excellent Future of Networking podcast with Martin Casado because (as he said) he prefers “having a technical discussion with arguments and not just throwing statements out there.”

He started with “Martin's view seems to be that network is all plumbing and all the intelligence should be in the applications.”

When I asked “Are there any truly QoS-aware routing protocols out there?” in one of my SD-WAN posts, Marcelo Spohn from ADARA Networks quickly pointed out that they have one – Dynamic Link-State Routing Protocol.

He also claimed that DLSP has no scalability concerns – more than enough reasons to schedule an online chat, resulting in Episode 40 of Software Gone Wild. We didn’t go too deep this time, but you should get a nice overview of what DLSP is and how it works.

::: jump-link Enjoy the podcast :::

Ethan Banks recently wrote a nice blog post detailing the benefits and drawbacks of traditional routing protocols and comparing them with their SD-WAN counterparts.

While I agree with everything he wrote, the comparison between the two isn’t exactly fair – it’s a bit like trying to cut the cheese with a chainsaw and complaining about the resulting waste.

Whenever I get asked about QoS in the data center, my stock reply is “bandwidth is cheaper than QoS-induced complexity.” This is definitely true in most cases, and ideally the elephant problems should be solved higher up in the application stack, not with network-layer kludges, but are there situations where you actually need data center QoS?

In the final part of our MPLS-focused discussion (now part of MPLS Essentials webinar), Seamus wanted to know how one could combine MPLS/VPN, MPLS-TE and QoS (for example, sending VoIP traffic for one customer over a different path).

Short answer: don’t even think about doing that. The added complexity is not worth whatever extra money you’ll be charging the customer (or not).

If you listen to the marketing departments of overlay virtual networking vendors, it looks like the world is a simple place: you deploy their solution on top of any IP fabric, and it all works.

You’ll hear a totally different story from the physical hardware vendors: they’ll happily serve you a healthy portion of FUD, hoping you swallow it whole, and describe in gory details all the mishaps you might encounter on your virtualization quest.

The funny thing is they’re all right (not to mention the really fun part when FUDders change sides ;).

My “Was it bufferbloat?” blog post generated an unexpected amount of responses, most of them focusing on a side note saying “it looks like there really are service providers out there that are clueless enough to reorder packets within a TCP session”. Let’s walk through them.

One of my readers opened another can of VMware vSwitch worms. He sent me this question:

If a VM were to set a COS value, would the vSwitch reset it to 0 as part of its process of building the dot1q header?

The nasty detail (as you probably know) is that 802.1p CoS value resides in the 802.1q (VLAN) tag.

The Mice and Elephants is a traditional QoS fable – latency-sensitive real time traffic (or request-response protocol like HTTP) stuck in the same queue behind megabytes of file transfer (or backup or iSCSI) traffic.

The solution is also well known – color the elephants pink (aka DSCP marking) and sort them into a different queue – until the reality intervenes.