The sysctl net.ipv6.conf.all.autoconf does not apply to "all"

Thank you for taking the time to report this bug and helping to make Ubuntu better. Now that the 7.10 Gutsy Gibbon release of Ubuntu is out, we were wondering if you can still reproduce this issue. Could you please download and try the new version of Ubuntu from http://www.ubuntu.com/getubuntu/download and report back your results. If the issue is still present in the new release, please attach the following information:

* uname -a > uname-a.log
* cat /proc/version_signature > version.log
* dmesg > dmesg.log
* sudo lspci -vvnn > lspci-vvnn.log

Please be sure to attach each file as a separate attachment. For more information regarding the kernel team bug policy, please refer to https://wiki.ubuntu.com/KernelTeamBugPolicies . Thanks again and we appreciate your help and feedback.

5 months with no reply. We are closing this bug report because it lacks the information we need to investigate the problem, as described in the previous comments. Please reopen it if you can give us the missing information, and don't hesitate to submit bug reports in the future. To reopen the bug report you can click on the current status, under the Status column, and change the Status back to "New". Thanks again!

Hello,

I´m reopening this bug as it seems to be affecting current versions of ubuntu too.
I´ve attached the requested logs as requested by Leann.
Note: I´m running ubuntu inside a virtual box environment.

Regards,
Christian

(version.log)

uname -a

dmesg.log

lspci-vvnn.log

Since the problem is now reported on 2.6.32, I'm opening it against "linux" and putting 2.6.20 back to invalid.

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

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This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

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I have observed this as a more general problem with any sysctl setting for "all" interfaces.

For example, try:

sysctl -a | grep '^net\.ipv4\.conf.*send_redirects'
sysctl -w net.ipv4.conf.all.send_redirects=0
sysctl -a | grep '^net\.ipv4\.conf.*send_redirects'
sysctl -w net.ipv4.conf.all.send_redirects=1
sysctl -a | grep '^net\.ipv4\.conf.*send_redirects'

It seems that setting conf.all does not have any effect on the individual conf.<interface> settings. This begs the question of what setting conf.all is supposed to do.

There is also conf.default which appears to be the value inherited when a new interface is created. To test:

sysctl -w net.ipv4.conf.all.send_redirects=1
sysctl -w net.ipv4.conf.default.send_redirects=0
brctl addbr br100
sysctl net.ipv4.conf.br100.send_redirects # it's 0

sysctl -w net.ipv4.conf.all.send_redirects=1
sysctl net.ipv4.conf.br100.send_redirects # it's still 0

sysctl -w net.ipv4.conf.all.send_redirects=0
sysctl -w net.ipv4.conf.default.send_redirects=1
brctl addbr br101
sysctl net.ipv4.conf.br101.send_redirects # it's 1
sysctl net.ipv4.conf.br100.send_redirects # it's still 0

This is sensible. Hence I can see how "default" is useful, but not "all".

Above tests done with Ubuntu 12.04.4 running kernel 3.8.0-36-generic

The answer for IPv4 was figured out here:
http://unix.stackexchange.com/questions/90443/sysctl-proc-sys-net-ipv46-conf-whats-the-difference-between-all-defau

The behaviour is non-obvious. For some settings the interface and 'all' settings are ANDed together; for others they are OR'd, for others the MAX is taken.

send_redirects is an OR, which means you can enable sending of redirects on all interfaces (conf.all.send_redirects=1) but you cannot disable sending them on all interfaces. In that case you have to set conf.all.send_redirects=0 *and* set each individual interface.

So in /etc/sysctl.conf you have to list all the interfaces which the host has (or may have) at startup time, if you want to disable sending of redirects on those interfaces. A tri-state setting for conf.all would be much more useful, but that's not what we have.

Now back to the original report, which was about net.ipv6.conf.all.autoconf=0. What is the intended behaviour from the kernel authors?

include/linux/inetdevice.h appears to have IPv4 settings only. For IPv6:

grep -R devconf_all net/ipv6

Unfortunately it's not obvious to me how "all" + interface-specific parameters interact for IPv6. There are some places where the two are explicitly combined: e.g.

[net/ipv6/ndisc.c]
                     (net->ipv6.devconf_all->proxy_ndp || idev->cnf.proxy_ndp) &&

I don't see anything similar for autoconf. However there is:

[net/ipv6/af_inet6.c]
MODULE_PARM_DESC(autoconf, "Enable IPv6 address autoconfiguration on all interfaces");

Closing this bug with Won't fix as this kernel / release is no longer supported.
Please feel free to open a new bug report if you're still experiencing this on a newer release (Bionic 18.04.3 / Disco 19.04)
Thanks!