https://matteocroce.it/tags/ssh/Recent content in Ssh on Matteo Croce personal homepageHugoen-USThu, 16 Apr 2026 01:21:14 +0200https://matteocroce.it/blog/ssh-low-qos/Thu, 16 Apr 2026 01:21:14 +0200https://matteocroce.it/blog/ssh-low-qos/<p>QoS stands for Quality of Service. Improvement is not implied.</p> <h2 id="symptoms">Symptoms</h2> <p>I&rsquo;ve been a happy OpenWrt user for 20 years, but due to a hardware failure I had to temporarily switch back to my ISP router.<br> After the swap, every <code>git pull</code> started hanging. No errors, just a timeout after a few minutes.</p> <h2 id="the-investigation">The Investigation</h2> <p>The usual suspects were checked first:</p> <ul> <li><strong>DNS</strong> - always the first suspect, but manual resolution with <code>dig</code> worked fine.</li> <li><strong>MTU/MSS clamping</strong> - second suspect, but usually also breaks HTTP downloads.</li> <li><strong>IPv6</strong> - I disabled IPv6 just in case, but the problem persisted.</li> <li><strong>Firewall rules</strong> - I could connect with netcat to github.com:22 and see the SSH banner.</li> </ul> <p>I didn&rsquo;t find any issues with general connectivity, so I focused on Git and noticed that some repositories were working while others weren&rsquo;t. Initially I thought that it could be a server-side issue, but the failing repositories were spread between GitHub and GitLab, so it was unlikely that both services had simultaneous issues.</p>