Linux
SSH ProxyJump: Reach a Server Through a Jump Host
A server that only accepts SSH from one static IP does not need your private key on that IP. Tested ProxyJump setups, the errors you will see and how to lock down the jump host.
Topic
networking
Linux
Xtables-addons: GeoIP, TARPIT and the psd Module I Ported
Extra iptables matches and targets the kernel never shipped: country blocking with geoip, a TARPIT decoy port, port knocking, and the psd scan detector I ported.
MySQL
Store IPv4 and IPv6 Together in MySQL With INET6_ATON()
One column for both address families: INET6_ATON() and INET6_NTOA(), IPv4-mapped addresses, correct sorting, indexed range queries and MariaDB's native INET6 type.
MySQL
Match an IPv4 Address Against a CIDR Subnet in MySQL
Store IPv4 addresses as INT UNSIGNED and test CIDR membership with a bitmask or, much faster on a big table, an indexed BETWEEN range on network and broadcast.
Linux
Find Which Process Is Listening on a Port in Linux
"Address already in use" again? How to find the owner of a port with ss, lsof and fuser, decode /proc/net/tcp by hand, and why some ports show no process.
MySQL
ipcalc() in MySQL: Network, Broadcast and Prefix From a Netmask
Work out the network, broadcast address and prefix length of an IPv4 address inside a query, using INET_ATON(), INET_NTOA() and a little bitwise arithmetic.