Author | Lightnews

Ben Cartwright-Cox @benjojo.bsky.social · Jun 5

New Blog!

There is lots of RFC1918 space out there, yet most people use the same 10 /24 subnets

I ended up having my OOB LAN collide with someone's home network a few weeks ago, and decided to find a new subnet to use that won't collide backed up with actual usage data!

Picking uncontested private IP subnets with usage data

blog.benjojo.co.uk

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Ben Cartwright-Cox @benjojo.bsky.social · May 27

On May 20th 2025 a BGP message was propagated that triggered some surprisingly disruptive behaviours with two major BGP implementations make up a lot of the internet.

In a new blog post, I will dissect what that message was, and my thoughts on how it happened:

blog.benjojo.co.uk/post/bgp-att...

BGP handling bug causes widespread internet routing instability

blog.benjojo.co.uk

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Reposted by Ben Cartwright-Cox

BGP.Tools @bgp.tools · Feb 12

After sitting on the decision for quite a while, bgp.tools will be switching away from posting updates on X.

Users can follow this account, or the fedi account @[email protected] instead

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 6

Some of it is the TCP behaviour that RFC 9687 is trying to address, but I would guess that only ~30% of them are due to this.

There is a upcoming follow up post around where/how I think the other 70% are coming from

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 5

New blog post!

Ever wondered about the process that grants RFC numbers for documents? Well, worry no more, introducing:

--

The “simple” 38 step journey to getting an RFC

blog.benjojo.co.uk/post/rfc-in-...

The "simple" 38 step journey to getting an RFC

blog.benjojo.co.uk

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Ben Cartwright-Cox @benjojo.bsky.social · Jan 22

Much like sisyphus is forced to roll a boulder up a hill for eternity, I am now getting payback for buying cheap QLC SSDs that I am seemingly vaporising at the moment

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Ben Cartwright-Cox @benjojo.bsky.social · Jan 11

It has been 0 days since someones Apple webcam "Reaction Effects" have triggered on a serious biz call

Ben Cartwright-Cox @benjojo.bsky.social · Jan 7

I've published a text version of my #37C3 lightning talk!

"The browsers biggest TLS mistake"

https://blog.benjojo.co.uk/post/browsers-biggest-tls-mistake

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 25

Happy xmas, see some of you soon at #37c3

(Bonus cat pic)

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 24

F👀D

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 24

I've got a lightning talk/rant coming up at #37C3!

Hope to see you there: https://pretalx.c3voc.de/37c3-lightningtalks/talk/XGML8T/

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 19

*bangs hands on table* DATA DATA DATA DATA DATA DATA DAT-

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 19

As far as I can tell where the Grindavík (Iceland) eruption has surfaced, is around 13km (as the crow flies) from one of the larger data centres in Iceland...

Must be some good disaster response emails going around at the moment!

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 14

Looks like Hetzner (24940) typo'd a BGP prepend (2490) when doing traffic engineering towards CoreBackBone (33891).

Woops. It makes it look like Raytheon are upstreams when they are not!

https://bgp.tools/prefix/95.216.0.0/16#connectivity

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 14

Finally got Office XP working, Look at this! WordArt never got better than this

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 12

Say hi to datacenter car park fox who was taking a break from the rain.

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 12

I like big cables and I cannot lie

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Ben Cartwright-Cox @benjojo.bsky.social · Dec 12

Hm, so a small DLR station takes "only" 25kW to run, based on this emergency generator readout

Ben Cartwright-Cox @benjojo.bsky.social · Nov 13

We are so close to 1.7B Unix epoch

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Ben Cartwright-Cox @benjojo.bsky.social · Nov 10

For some reason the Ceph dashboard is like a fish tank, I literally just keep staring at it.

Especially right now as it's doing a transfer from the old storage machine to the new setup (for bgp.tools)

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Ben Cartwright-Cox @benjojo.bsky.social · Nov 10

Ooooh, the 0th longitude laser is very visible tonight in London

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Ben Cartwright-Cox @benjojo.bsky.social · Oct 24

My NANOG 89 talk on the internal operations of bgp.tools is up on youtube!

https://www.youtube.com/watch?v=83NJllv0q9U

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Ben Cartwright-Cox @benjojo.bsky.social · Oct 24

My NANOG 89 version of my "Discovering flaws in BGP error handling" talk is now up on youtube!

https://www.youtube.com/watch?v=-_VBehyNwqg

Ben Cartwright-Cox @benjojo.bsky.social · Oct 23

Graph improvements to bgp.tools!

On the bgp.tools BGP propagation graphs there are now names attached to the network boxes to help faster comprehension.

In addition, font profiles for the graphs have been normalised between Linux/Windows/Mac

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Ben Cartwright-Cox @benjojo.bsky.social · Oct 20

Google maps appears to think I can walk on water?