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Blog Posts in November 2015

Fibbing: OSPF-Based Traffic Engineering with Laurent Vanbever

You might be familiar with the idea of using BGP as an SDN tool that pushes forwarding entries into routing and forwarding tables of individual devices, allowing you to build hop-by-hop path across the network (more details in Packet Pushers podcast with Petr Lapukhov).

Researchers from University of Louvain, ETH Zürich and Princeton figured out how to use OSPF to get the same job done and called their approach Fibbing. For more details, listen to Episode 45 of Software Gone Wild podcast with Laurent Vanbever (one of the authors), visit the project web site, or download the source code.

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Ethernet Checksums Are Not Good Enough for Storage (Updated)

A while ago I described why some storage vendors require end-to-end layer-2 connectivity for iSCSI replication.

TL&DR version: they were too lazy to implement iSCSI checksums and rely on Ethernet checksums because TCP/IP checksums are not good enough.

It turns out even Ethernet checksums fail every now and then.

2015-12-06: I misunderstood the main technical argument in Evan’s post. The real problem is that switches recalculate CRC, so the Ethernet CRC is no longer end-to-end protection mechanism.

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Blogging Rule#1: Be Useful

I love stumbling upon new networking-focused blogs. Many of my old friends switched to the dark side vendors and stopped blogging, others simply gave up, and it seems like there aren’t that many engineers that would like to start this experiment.

One of the obvious first questions is always “what should I write about” and my reply is always “it doesn’t really matter – make sure it’s useful.”

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Can You Afford to Reformat Your Data Center?

I love listening to the Datanauts podcast (Ethan and Chris are fantastic hosts), starting from the very first episode (hyper-converged infrastructure) in which Chris made a very valid comment along the lines of “with the hyper-converged infrastructure it’s possible to get so many things done without knowing too much about any individual thing…” and I immediately thought “… and what happens when it fails?

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DMVPN Split Default Routing and Internet Access

One of the engineers listening to my DMVPN webinars sent me a follow-up question (yes, I always try to reply to them) asking how to implement direct Internet access from the spoke sites (aka local exit) in combination with split default routing you have to use in DMVPN Phase 2 or Phase 3 networks.

It’s really simple: either you have a design requirement that requires split default routing, or you don’t.

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Presentation: All You Need Are Two Switches

I was asked to present a data-center-related talk last week and decided to focus on one of my favorite topics: because most people don’t have more than a few hundred servers in their data center, they don’t need more than two switches (or a rack of servers).

Not surprisingly, an equipment reseller sitting in the room was not amused.

The video and the slide deck are already online, but there’s a minor challenge: the whole event was in Slovenian ;) However, I plan to record the same topic in English once my SDN travels stop.

see 2 comments

Test-Driven Network Development with Michael Kashin on Software Gone Wild

Imagine you’d design your network by documenting the desired traffic flow across the network under all failure conditions, and only then do a low-level design, create configurations, and deploy the network… while being able to use the desired traffic flows as a testing tool to verify that the network still behaves as expected, both in a test lab as well as in the live network.

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The Numerous Levels of SDN Reality

A newbie exploring the mythical lands of SDN might decide to start at the ONF definition of SDN, which currently (November 2015) starts with a battle cry:

The physical separation of the network control plane from the forwarding plane, and where a control plane controls several devices.

The rest of that same page is what I’d call the marketing definition of SDN: directly programmable, agile, centrally managed, programmatically configured, open standards based and vendor-neutral.

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There’s a Problem with IPv6 Multihoming

In an amazing turn of events, at least one IETF working group recognized we have serious problems with IPv6 multihoming. According to the email Fred Baker sent to a number of relevant IETF working groups:

PI multihoming demonstrably works, but PA multihoming when the upstreams implement BCP 38 filtering requires the deployment of some form of egress routing - source/destination routing in which the traffic using a stated PA source prefix and directed to a remote destination is routed to the provider that allocated the prefix. The IETF currently has no such recommendation, or consensus that it should have.

Here are a few really old blog posts just in case you don’t know what I’m talking about (and make sure you read the comments as well):

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Learn to Speak Your Peer’s Language with ipSpace.net Webinars

One of the reasons I started creating ipSpace.net webinars was to help networking engineers grasp the basics of adjacent technologies like virtualization and storage. Based on feedback from an attendee of my Introduction to Virtual Networking webinar it works:

I am completely on the Network side of the house and understand what I need to build for Storage/Data replication, but I really never thoroughly understood why. This allowed me to have a coherent discussion with my counterparts in DB and Storage and some of the pitfalls that can occur if we try to cowboy the network design.

Recommendation: if you have a similar problem, start with Introduction to Virtual Networking and continue with Data Center 3.0 webinar.

Stretched Firewalls across Layer-3 DCI? Will the Madness Ever Stop?

I got this question from one of my readers (and based on these comments he’s not the only one facing this challenge):

I was wondering if you can do a blog post on Cisco's new ASA 5585-X clustering. My company recently purchased a few of these with the intent to run their cross data center active/active firewalls but found out we cannot do this without OTV or a layer 2 DCI.

A while ago I expressed my opinion about these ideas, but it seems some people still don’t get it. However, a picture is worth a thousand words, so maybe this will work:

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