Blog Posts in November 2011
For whatever reason I decided to start my Junos experience with a very simple IS-IS network – four core routers from my Building IPv6 Service Provider Core webinar. As Junosphere doesn’t support serial or POS interfaces, I migrated all links to Gigabit Ethernet and added a point-to-point GE link between PE-A and PE-B.
Dan sent me an interesting comment after watching my Data Center 3.0 webinar:
I have a different view regarding VMware vSwitch. For me its the best thing happened in my network in years. The vSwitch is so simple, and its so hard to break something in it, that I let the server team to do what ever they want (with one small rule, only one vNIC per guest). I never have to configure a server port again :).
As always, the right answer is “it depends” – what kind of vSwitch you need depends primarily on your requirements.
Jónatan Þór Jónasson took the time to implement Wake-on-LAN functionality using UDP support introduced in Cisco IOS Tcl in release 15.1(1)T. He found a TCL/TK example of a magic packet being sent, used that as a base, and with small modifications got it to work on his router. Here‘s his code (it’s obviously a proof-of-concept, but you need just a few more lines to get a working Tclsh script):
If you read my Twitter stream, you’ve probably realized I’d been stupid enough to decide to do another multi-vendor experiment: I’m trying to figure out whether an old grump can adapt to a MacBook Air.
Warning: What follows is a rant. You might want to skip this one and read something more technical.
Many service providers choosing IS-IS as their IGP use it within a single area (or at least run all routers as L1L2 routers). Multi-level IS-IS design is a royal pain, more so in MPLS environments where every PE-router needs a distinct route for every BGP next hop (but of course there’s a nerd knob to disable L1 default route in IS-IS). Moreover, MPLS TE is reasonably simple only within a single level (L1 or L2).
I’m positive at least some service providers do something as stupid as I usually did – deploy IS-IS with default settings using a configuration similar to this one:
My Junos versus Cisco IOS: Explicit versus Implicit received a huge amount of helpful comments, some of them slightly philosophical, others highly practical – from using interfaces all combined with interface disable in routing protocol configuration, to using configuration groups (more about that fantastic concept in another post).
However, understanding what’s going on is not the same as being able to explain it in one sentence ... and Dan (@jonahsfo) Backman beautifully nailed that one.
You’re probably tired of this story by now: public IPv4 addresses are running out, lots of content is available only over IPv4, and so the service providers use NAT to give new clients (with no public IPv4 address) access to old content. It doesn’t matter which NAT variant the service provider is using, be it Carrier Grade Nat (CGN), NAT64, DS-Lite or A+P, the crucial problem is always the same: multiple users are hidden behind a single source IP address.
Best design information of the week: Chris Marget write a series on practical data center network designs (10GE servers connected to Nexus 5K) – Part 1 describes ToR Nexus 5596, Part 2 ToR Nexus 5548 and Part 3 a pair of Nexus 5548 with ToR FEX.
And here’s the rest of my Inbox collection:
My first Junos labbing project was an IPv6 backbone; I wanted to create a simple single-area IS-IS/BGP-free backbone running LDP and MPLS, and using 6PE for IPv6 connectivity. Needless to say, even though I read the excellent Day One books (highly recommended: Exploring IPv6, Advanced IPv6 configuration and Deploying MPLS), I stumbled on almost every step.
Michel sent me a detailed e-mail describing both his enthusiasm with vPC and the headaches consistency checker is causing him. Here’s the good part:
Nexus vPC seems like a perfect solution for real multi-chassis etherchannel. At work we're using it extensively on a few pairs of Nexus 7000's.
... and then it turns sour:
However, there is one MAJOR drawback with vPC at this time, it's the way the consistency checker works (or rather, does not work). We've come across two specific situations where consistency checker will bring down your beautiful and redundant vPC link, and we've found no way around.
Here are his problems:
The comments igp2bgp and Tiziano Tofoni made to my LDP-IGP Synchronization in MPLS Networks post prompted me to look deeper into basic Junos MPLS configuration and LDP behavior. As expected, there are some significant differences between Cisco’s and Juniper’s LDP implementations (and, as is usually the case, they’re both strictly conformant with RFC 5036).
One of the comments I usually get about OpenFlow is “sounds great and I’m positive Yahoo! and Google will eventually use it, but I see no enterprise use case.” (see also this blog post). Obviously nobody would go for a full-blown native OpenFlow deployment and we’ll probably see hybrid (ships-in-the-night) approach more often in research labs than in enterprise networks, but there’s always the integrated mode that allows you to add OpenFlow-based functionality on top of existing networking infrastructure.
A reader of my blog planning to migrate his network from a traditional BGP-everywhere design to a BGP-over-MPLS one wondered about potential unexpected consequences. The MTU implications of introducing MPLS in a running network are usually well understood (even though you could get some very interesting behavior); if you can, increase the MTU size by at least 16 bytes (4 labels) and check whether MTU includes L2 header. Another somewhat more mysterious beast is the interaction between IGP and LDP that can cause traffic disruptions after the physical connectivity has been reestablished.
During the last days there have been rumors of flying pigs and open speculations whether I’d rename my blog to junoshints or junioshints due to my Junos-related posts. When even my wife told me to get my act together, it was time to move ... and you can see the first changes at the top left corner of the screen.
Yesterday’s 6th Slovenian IPv6 Summit was (as always) full of awesome presentations, this time coming straight from some of the IPv6 legends: check the ones from Eric Vyncke (and make sure you read his IPv6 Security book), Randy Bush and Mark Townsley. The epic moment, however, was the “I was getting bored” part of Eric’s presentation (starts around 0:50:00). This is (in a nutshell) what he did:
Abner (@abnerg) Germanov surprised us all at the end of Juniper’s presentation at Networking Tech Field Day when he announced Junosphere access for all the delegates – after a year of nagging, I would finally be able to touch Junos. However, instead of taking it easy and studying the excellent Junos Day One books (which I also did – if you’re new to Junos you should definitely start there; they are well worth reading), I decided to take a more geeky approach.
Big Switch Networks is one of those semi-stealthy startups that like to hint at what they’re doing without actually telling you anything, so I was very keen to meet Kyle Forster and Guido Appenzeller during the OpenFlow Symposium and asked them a simple question: “can you explain in 3 minutes what it is you’re doing?”
The “discovery of the week” award goes to Terry Slattery for pointing out the dangers of bufferbloat while investigating TCP retransmissions (part 1 and part 2). BTW, in the end, he figured out it was just an overloaded Gigabit Ethernet linecard.
Did you ever want to have a high-level overview of how 3G/4G mobile networks work? Where GGSN and SGSN fit in? What the PDP contexts are ... and why you need two for dual-stack connectivity? All that (and a lot more) is explained in very well written IETF draft IPv6 in 3GPP Evolved Packet System. Reading highly recommended.
I stumbled upon VMsafe Network API (the API formerly known as dvFilter) while developing my VMware Networking Deep Dive webinar, set up the vShield App 4.1 in a lab, figured out how it works (including a few caveats), and assumed that’s how most virtual firewalls using dvFilter work. Boy was I wrong!
An engineer attending my VMware Networking Deep Dive webinar has asked me a tough question that I was unable to answer:
What happens if a VM running within a vSphere host sends a BPDU? Will it get dropped by the vSwitch or will it be sent to the physical switch (potentially triggering BPDU guard)?
I got the answer from visibly harassed Kurt (@networkjanitor) Bales during the Networking Tech Field Day; one of his customers has managed to do just that.
Update 2011-11-04: The post was rewritten based on extensive feedback from Cisco, VMware and numerous readers.
Finally someone decided to make IPv6 flow label useful. First they had to justify why they want to change it, and then modify the definition (way too much work for a field nobody ever used). Planned use is to enhance ECMP load balancing, both in native IPv6 environments (where using the flow label is faster than digging deep into variable-length IPv6 extension headers) and (even more importantly) in tunneled environments, where the flow label propagates the entropy from the tunnel payload into the envelope header.
I hope you never believed the “OpenFlow networking nirvana” hype in which smart open-source programmable controllers control dumb low-cost switches, busting the “networking = mainframes” model and bringing the Linux-like golden age to every network. As the debates during the OpenFlow symposium clearly illustrated, the OpenFlow reality is way more complex than it appears at a first glance.
To make it even more interesting, at least four different models for OpenFlow deployment have already emerged:
A few weeks ago I delivered a short L2 DCI WebEx presentation to CCIE Club Poland. I took the L2 part of my Data Center Interconnect webinar and added 15 minutes of L2 DCI mythbusting (yes, it took me that long to explain what @reillyusa summarized in a single tweet). Here’s that part of the presentation; for the rest, buy a recording of my Data Center Interconnect webinar (it contains much more than just L2 DCI).