Ben Cartwright-Cox

Picking uncontested private IP subnets with usage data

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!

BGP handling bug causes widespread internet routing instability

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...

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 @bgptools@bgp.tools instead

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

The "simple" 38 step journey to getting an RFC

New blog post!

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

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The “simple” 38 step journey to getting an RFC

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

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

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

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

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

(Bonus cat pic)

F👀D

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

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

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

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!

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

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

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

I like big cables and I cannot lie

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

We are so close to 1.7B Unix epoch

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)

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

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


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

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

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

Google maps appears to think I can walk on water?

Finally a interface perfect for the gentoo users out there

"why do we even have those on an aircraft carrier"

(Taken on the USS Midway)

ah yes, IPv4 prices are coming back down, nature is healing

Bought a 7$ fidget toy while trying to find a C13 cable in the US

Can somebody check in with the BBC sports people to see if they're all right?