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Category: LAN

History of Ethernet Encapsulations

Henk Smit conscientiously pointed out a major omission I made when summarizing Peter Paluch’s excellent description of how bits get parsed in network headers:

EtherType? What do you mean EtherType? There are/were 4 types of Ethernet encapsulation. Only one of them (ARPA encapsulation) has an EtherType. The other 3 encapsulations do not have an EtherType field.

What is he talking about? Time for another history lesson1.

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Just Out: Metro- and Carrier Ethernet Encryptors Market Overview

Christoph Jaggi has just published the third part of his Metro- and Carrier Ethernet Encryptor trilogy: the 2015 market overview. Public versions of all three documents are available for download on his web site:

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IPv6 Neighbor Discovery (ND) and Multicast Listener Discovery (MLD) Challenges

A few days ago Garrett Wollman published his exasperating experience running IPv6 on large L2 subnets with Juniper Ex4200 switches, concluding that “… much in IPv6 design and implementation has been botched by protocol designers and vendors …” (some of us would forcefully agree) making IPv6 “…simply unsafe to run on a production network…

The resulting debate on Hacker News is quite interesting (and Andrew Yourtchenko is trying hard to keep it close to facts) and definitely worth reading… but is ND/MLD really as broken as some people claim it is?

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First-Hop IPv6 Security Features in Cisco IOS

I wanted to figure out how to use IPv6 DAD proxy in PVLAN environments during my seaside vacations, and as I had no regular Internet access decided to download the whole set of IPv6 configuration guides while enjoying the morning cup of coffee in an Internet café. Opening the IPv6 First-Hop Security Configuration Guide was one of the most pleasant (professional) surprises I had recently.

One word summary: Awesome.

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VRRP, Anycasts, Fabrics and Optimal Forwarding

The Optimal L3 Forwarding with VARP/VRRP post generated numerous comments, ranging from technical questions about VARP (more about that in a few days) to remarks along the lines of “you can do that with X” or “vendor Y supports Z, which does the same thing.” It seems I’ve opened yet another can of worms, let’s try to tame and sort them.

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VLANs are the wrong abstraction for virtual networking

Are you old enough to remember the days when operating systems had no file system? Fortunately I never had to deal with storing files on one of those (I was using punch cards), but miraculously you can still find the JCL DLBL/EXTENT documentation online.

On the other hand, you probably remember the days when a SCSI LUN actually referred to a physical disk connected to a computer, not an extensible virtual entity created through point-and-click exercise on a storage array.

You might wonder what the ancient history has to do with virtual networking. Don’t worry we’re getting there in a second ;)

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Where Is my VLAN Provisioning Application?

Yesterday I wrote that it’s pretty easy to develop a VLAN provisioning application (integrating it with vCenter or System Center earns you bonus points, but even that’s not too hard), so based on the frequent “I hate using CLI to provision VLANs” rants you might wonder where all the startups developing those applications are. Simple answer: there’s no reasonably-sized market. How would I know that? We’ve been there.

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VXLAN and OTV: I’ve been suckered

When VXLAN came out a year ago, a lot of us looked at the packet format and wondered why Cisco and VMware decided to use UDP instead of more commonly used GRE. One explanation was evident: UDP port numbers give you more entropy that you can use in 5-tuple-based load balancing. The other explanation looked even more promising: VXLAN and OTV use very similar packet format, so the hardware already doing OTV encapsulation (Nexus 7000) could be used to do VXLAN termination. Boy have we been suckered.

Update 2015-07-12: NX-OS 7.2.0 supports OTV encapsulation with VXLAN-like headers on F3 linecards. See OTV UDP Encapsulation for more details (HT: Nik Geyer).

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QFabric Lite

2021-01-03: Even though QFabric was an interesting architecture (and reverse-engineering it was a fun intellectual exercise), it withered a few years ago. Looks like Juniper tried to bite off too much.

QFabric from Juniper is probably the best data center fabric architecture (not implementation) I’ve seen so far – single management plane, implemented in redundant controllers, and distributed control plane. The “only” problem it had was that it was way too big for data centers that most of us are building (how many times do you need 6000 10GE ports?). Juniper just solved that problem with a scaled-down version of QFabric, officially named QFX3000-M.

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