Change Details

The code below walks IPv6 tree every 60 seconds and looks into the routes with non-zero expiration time (typically, redirected routes). For each such route it sets `RTF_PROBEMTU` flag at the expiration time. No other part of the kernel checks for `RTF_PROBEMTU` flag. The original [commit](https://github.com/kame/kame/blob/eb17921deb6f523f46009f823dbdb01b0b02ee3c/kame/sys/netinet6/in6_rmx.c) (actually, the first reference I was able to find), dates 5 Aug 1999. As far as I understood, this flag was used as a hint for the TCP to walk through it MTU table and refresh MTU values there accordingly. [BSDI tcp_timer.c](http://daedalus.cs.berkeley.edu/software/web-tcp/asym/tcp_timer.c) [BSDI tcp_subr.c](http://daedalus.cs.berkeley.edu/software/web-tcp/session/tcp_subr.c) There is no such functionality in the kernel anymore. Lastly, `RTF_PROBEMTU `was [defined](https://github.com/kame/kame/blob/51ca2998733f77d51c565d599e787522256722ac/kame/sys/netinet6/icmp6.h) 21 years ago, 30 Jun 1999, as `RTF_PROTO1`. `RTF_PROTO1` is a de-facto standard indication of a route installed by a routing daemon for a last decade.

The code below walks IPv6 tree every 60 seconds and looks into the routes with non-zero expiration time (typically, redirected routes). For each such route it sets `RTF_PROBEMTU` flag at the expiration time. No other part of the kernel checks for `RTF_PROBEMTU` flag. The original [commit](https://github.com/kame/kame/blob/eb17921deb6f523f46009f823dbdb01b0b02ee3c/kame/sys/netinet6/in6_rmx.c) (actually, the first reference I was able to find), dates 5 Aug 1999. As far as I understood, this flag was used as a hint for the TCP to walk through it MTU table and refresh MTU values there accordingly. [BSDI tcp_timer.c tcp_slowtimo()](http://daedalus.cs.berkeley.edu/software/web-tcp/asym/tcp_timer.c) [BSDI tcp_subr.c tcp_agepathmtu()](http://daedalus.cs.berkeley.edu/software/web-tcp/session/tcp_subr.c) There is no such functionality in the kernel anymore. Lastly, `RTF_PROBEMTU`was [defined](https://github.com/kame/kame/blob/51ca2998733f77d51c565d599e787522256722ac/kame/sys/netinet6/icmp6.h) 21 years ago, 30 Jun 1999, as `RTF_PROTO1`. `RTF_PROTO1` is a de-facto standard indication of a route installed by a routing daemon for a last decade. NetBSD removed it in [2011](https://mail-index.netbsd.org/tech-net/2011/07/07/msg002720.html).

The code below walks IPv6 tree every 60 seconds and looks into the routes with non-zero expiration time (typically, redirected routes). For each such route it sets `RTF_PROBEMTU` flag at the expiration time. No other part of the kernel checks for `RTF_PROBEMTU` flag. The original [commit](https://github.com/kame/kame/blob/eb17921deb6f523f46009f823dbdb01b0b02ee3c/kame/sys/netinet6/in6_rmx.c) (actually, the first reference I was able to find), dates 5 Aug 1999. As far as I understood, this flag was used as a hint for the TCP to walk through it MTU table and refresh MTU values there accordingly. [BSDI tcp_timer.c tcp_slowtimo()](http://daedalus.cs.berkeley.edu/software/web-tcp/asym/tcp_timer.c) [BSDI tcp_subr.c tcp_agepathmtu()](http://daedalus.cs.berkeley.edu/software/web-tcp/session/tcp_subr.c) There is no such functionality in the kernel anymore. Lastly, `RTF_PROBEMTU `was [defined](https://github.com/kame/kame/blob/51ca2998733f77d51c565d599e787522256722ac/kame/sys/netinet6/icmp6.h) 21 years ago, 30 Jun 1999, as `RTF_PROTO1`. `RTF_PROTO1` is a de-facto standard indication of a route installed by a routing daemon for a last decade. NetBSD removed it in [2011](https://mail-index.netbsd.org/tech-net/2011/07/07/msg002720.html).