https://rickvanderzwet.nl/ Blog posts tagged 'security' (subset of rickvanderzwet.nl) https://rickvanderzwet.nl/blog/2026/10/12/ssh-concentrator-port-knocking/ ## Introduction I run a backup machine at a remote location: stuck behind NAT, no control over the upstream firewall. What works for me is a reverse SSH tunnel to a machine I do control, with port knocking in front of the tunnel endpoint. An earlier attempt at knocking here had been running for yea... Mon, 12 Oct 2026 21:46:00 +0000 https://rickvanderzwet.nl/blog/2026/10/12/ssh-concentrator-port-knocking/ https://rickvanderzwet.nl/blog/2021/04/28/hardening-web-services/ Following the SIDN blogposts on [implementing SPF, DKIM and DMARC in PostFix](https://www.sidn.nl/en/news-and-blogs/hands-on-implementing-spf-dkim-and-dmarc-in-postfix) and [implementing DANE in Postfix](https://www.sidn.nl/en/news-and-blogs/hands-on-implementing-dane-in-postfix) I got myself inter... Wed, 28 Apr 2021 14:53:00 +0000 https://rickvanderzwet.nl/blog/2021/04/28/hardening-web-services/