A VoIP phone at home: The tech details on leaving your phone company

Introduction This is some information and hard-learned wisdom I collected while setting up an Israeli phone number for use with a VoIP phone, so I can accept calls with a regular Israeli phone number and also make outbound calls. Important to note is that I did this without the local ISPs that provide this service. [...]

MySQL, OOM killer, overcommitting and other memory related issues

It started with an error message This post is a bit of a coredump of myself attempting to resolve a sudden web server failure. And even more important, understand why it happened (check on that) and try avoiding it from happening in the future (not as lucky there). I’ve noticed that there are many threads [...]

AudioCodes MP202B hacking notes (Netvision)

This is a no-go These are notes during my failed attempts to turn an old (2011?) Israeli ISP provider’s SIP adapter (MP202B, provided by Netvision) into one that works with any SIP provider. The first step is to get access of its configuration, and that’s exactly where it stopped. Netvision has taken action to prevent [...]

Add-on icons vanished after Firefox upgrade

Don’t get me wrong: I didn’t upgrade Firefox. It upgraded itself suddenly into Firefox 68.o Quantum. How did I notice? Not because it became any better, but because suddenly things stopped working. And I got logged out from several sites. For example, my Adblocker and other add-on suddenly vanished. Checking the add-on settings, the relevant [...]

Setting up your own authoritative DNS server jots

What’s this? These are somewhat random jots I made while setting up an authoritative BIND server, so that a simple VPS machine can function standalone. Well, almost standalone, as it takes some help from a slave DNS to supply the second DNS entry. But even if that slave goes away suddenly, the show will go [...]

The art of setting up a sendmail server on Debian 8

But why? Fact number one: Running your own mail server is the most likely cause for messing up, and that can mean an intrusion to the server or just turning it into a public toilet for spam. Nevertheless, if mail delivery is important to you, there’s probably no way around. And I’m not talking about [...]

Digging to the root with DNS queries

Introduction This is an explicit walkthrough on how a domain name is resolved. Doing the recursion manually, that is. And then some remarks on the mess with DNS glue records. Getting the root servers $ dig NS . ; <<>> DiG 9.11.3-1ubuntu1.2-Ubuntu <<>> NS . ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: [...]

The SPF, DKIM and DMARC trio: Making your email appear decent

Intro Whether you just want your non-Gmail personal email to get through, or you have a website that produces transactional emails (those sent by your site or web app), there’s a long fight with spam filters ahead. The war against unsolicited emails will probably go on as long as email is used, and it’s an [...]

SMTP tidbits for the to-be postmaster

This is a quick overview of the parts of an SMTP session that are relevant to SPF and mail server setup. Just a sample SMTP session For a starter, this is what an ESMTP session between two mail servers talking on port 25 can look like (shamelessly copied from this post, which also shows how [...]

Perl, DBI and MySQL wrongly reads zeros from database

TL;DR: SELECT queries in Perl for numerical columns suddenly turned to zeros after a software upgrade. This is a really peculiar problem I had after my web hosting provider upgraded some database related software on the server: Numbers that were read with SELECT queries from the database were suddenly all zeros. Spoiler: It’s about running [...]