Category Archives: Network Technologies

Network Technologies

The IT Detective agency: the case of the incompatible sftp client

Intro I was asked for assistance with this sftp problem: $ sftp <user@host> DH_GEX group out of range: 1536 !< 1024 !< 8192 Couldn’t read packet: Connection reset by peer We actually spoke with the operator of the sftp server … Continue reading

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drjohnstechtalk now uses HTTP Strict Transport Security, HSTS

Intro I was reading about a kind of amazingly thorough exploit which could be done using a Raspberry Pi zero. Physical access is required, but the scope of what this guy has figured out and put together is really amazing. … Continue reading

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Roll your own dynamic DNS update service

Intro I know my old Cisco router only has built-in support for two dynamic DNS services, dyndns.org and TZO.com. Nowadays you have to pay for those, if even they work (the web site domain names seem to have changed, but … Continue reading

Posted in CentOS, DNS, Linux, Network Technologies, Raspberry Pi, Security, Web Site Technologies | Tagged , , , | Leave a comment

Who’s using the UK Ministry of Defence’s IP addresses?

Intro When I first came upon a spear phishing email a few months ago which originated from the UK’s Ministry of Defence I thought that was pretty queer. Like, how ironic that an invoice scam is coming from a Defense … Continue reading

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Internet Explorer can’t access https page – maybe a client CERT is needed?

Intro I don’t see such issues often, but today two came to my attention. Both are quasi-government sites. Here’s an example of what you see when testing with your browser if it’s Internet Explorer: The details Just for the fun … Continue reading

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IP address wall of shame

Intro It can be very time-consuming to report bad actors on the Internet. The results are unpredictable and I suppose in some cases the situation could be worsened. Out of general frustration, I’ve decided to publicly list the worst offenders. … Continue reading

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The IT Detective Agency: the case of the mysterious reset

Intro An F5 BigIP load balancer equipped with web application firewall worked for everyone, except one app used by one customer. What was going wrong? Packet trace I always do a packet trace when there is nothing else to go … Continue reading

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Idea for free web server certificates: Let’s Encrypt

Intro I’ve written various articles about SSL. I just came across a way to get your certificates for free, letsencrypt.org. But their thing is to automate certificate management. I think you have to set up the whole automated certificate management … Continue reading

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Strange problem with Internet fiber connection

Intro Yesterday the company I’ve been consulting for had a partial outage with their multi-gigabit fiber connection with TWC business class in North Carolina. We’ve never seen an outage with these characteristics. The details The outage was mostly unnoticed but … Continue reading

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Quick Tip: Why Windows traceroute works better than Linux

Intro We noticed when debugging with the always useful tool traceroute (tracert on Windows systems) that we got more responsive results from Windows than from a Linux server on the same or nearby network. Finally I decided to look into … Continue reading

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