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Blog Posts in March 2013

IPv6 Source Address Validation Improvement

We learned how to deal with ARP and IP spoofing in IPv4 networks. Every decent switch has DHCP snooping, ARP protection and IP source guard (or whatever the features are called) ... but validating source IPv6 addresses in security-conscious environments or public multi-access networks remains a major headache.

It would be pretty easy to solve the problem with a central controller, but IETF decided to go another way and developed yet-another framework: Source Address Validation Improvements (SAVI). For more information, watch the following video from IPv6 Security webinar in which Eric Vyncke describes the intricacies of SAVI in great details.

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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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Does dedicated iSCSI infrastructure make sense?

Chris Marget recently asked a really interesting question:

I've encountered an environment where the iSCSI networks are built just like FC networks: Multipathing software in use on servers and storage, switches dedicated to "SAN A" and "SAN B" VLANs, and full isolation of paths (redundant paths) between server and storage. I understand creating a dedicated iSCSI VLAN, but why would you need two? Isn’t the whole thing running on top of TCP? Am I missing something?

Well, it actually makes sense in some mission-critical environments.

Update 2015-12-06: Ethernet checksums are not a workaround for lack of iSCSI-level checksums. If your iSCSI solution doesn't support application-level checksum, your data might be at risk

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Happy Eyeballs – Happiness Defined by Your Perspective

It seems that most people not having a vested interest in status quo agree the socket API is broken. After all, why should every single application ever written have to deal with the idiosyncrasies of two address families?

Not surprisingly, the browser vendors got sick and tired of waiting for a fixed API or a standardized session layer (nothing happened in the last two decades) and decided to implement happy eyeballs – a simple mechanism that creates two TCP sessions (one over IPv4, another one over IPv6) and uses whichever one works better.

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Start Reading V6OPS Documents

You might not have to deploy IPv6 in your network tomorrow (if you’re an ISP I sincerely hope you do), but that’s no excuse for not getting prepared for the eventual inevitable deployment (Tom Hollingsworth has way more to say on this topic).

Don’t believe in the “inevitable” part? Maybe you should spend some time with people who were running SNA and IPX networks two decades ago and living in blissful IP denial.

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Controller-Based Packet Forwarding in OpenFlow Networks

One of the attendees of the ProgrammableFlow webinar sent me an interesting observation:

Though there is separate control plane and separate data plane, it appears that there is crossover from one to the other. Consider the scenario when flow tables are not programmed and so the packets will be punted by the ingress switch to PFC. The PFC will then forward these packets to the egress switch so that the initial packets are not dropped. So in some sense: we are seeing packet traversing the boundaries of typical data-plane and control-plane and vice-versa.

He’s absolutely right, and if the above description reminds you of fast and process switching you’re spot on. There really is nothing new under the sun.

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NEC ProgrammableFlow Scalability Features

Once you get rid of spanning tree and associated kludges (not too hard in OpenFlow-based networks), BUM flooding becomes your biggest enemy. NEC’s engineers implemented some interesting features in the ProgrammableFlow switches and controllers: rate-limiting of unknown unicast frames, flooding control, and ARP snooping (if only they’d go for ARP proxy).

3 & 5 Years Ago (December 2012)

The most popular posts from December 2007: Display open TCP and UDP ports on Cisco IOS, explanation of RIB failure and why password recovery might fail. It seems this blog has changed quite a bit in the last five years.

December 2009 had some interesting ones: role of certifications in the hiring process and a switching-is-a-stupid-marketing-term rant (it seems like nothing has changed in the last three years). Then there was a storage networking is still emulating a flat cable rant and hilarious ten steps of small LAN design.

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