On a machine without IPv6 support (IPv6 disabled in the kernel, and no IPv6 addresses), how to prevent programs from using IPv6 by default?
For instance, with wget, I can provide the -4 option: citron% wget -4 http://joooj.vinc17.net --2026-09-08 04:50:12-- http://joooj.vinc17.net/ Resolving joooj.vinc17.net (joooj.vinc17.net)... 155.133.131.76 Connecting to joooj.vinc17.net (joooj.vinc17.net)|155.133.131.76|:80... connected. HTTP request sent, awaiting response... 200 OK Length: 10701 (10K) [text/html] Saving to: ‘index.html’ index.html 100%[===================>] 10.45K --.-KB/s in 0s 2026-09-08 04:50:12 (149 MB/s) - ‘index.html’ saved [10701/10701] But a few seconds later without this option: citron% wget http://joooj.vinc17.net --2026-09-08 04:50:18-- http://joooj.vinc17.net/ Resolving joooj.vinc17.net (joooj.vinc17.net)... 2001:4b99:1:3:216:3eff:fe20:ac98 Connecting to joooj.vinc17.net (joooj.vinc17.net)|2001:4b99:1:3:216:3eff:fe20:ac98|:80... failed: Address family not supported by protocol. This is bad. I remember that in the past, I was using /etc/gai.conf on some machine, but strace shows here that this file isn't accessed. This is a Debian 12 (bookworm) machine, with nscd running. This issue is fully reproducible for a few hours. Then it disappears... before reappearing later. All the machines on the local network (same config) seem to be affected, but not at the same time. This seems random and may be related to DNS failures ("dig" sometimes returns SERVFAIL), but I cannot see how this could be explain the above behavior. -- Vincent Lefèvre <[email protected]> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / Pascaline project (LIP, ENS-Lyon)
