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mv
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PostPosted: Thu Sep 12, 2013 7:56 am    Post subject: No ipv6 with systemd and others Reply with quote

This appears like a rather stupid question:

Why would somebody want to enable IPv6 support in kernel on a home system if the internet provider and local modem do not support it?

I thought this question is stupid, since the answer should be obviously that you do not need it if you do not run an ipv6 network directly.
However, the systemd ebuild and related Wkis say that you must enable it in the kernel, systemd gives an error message when it is not enabled.
Also other programs seem to require it, e.g. dhcpcd defaults to ip4vll (despite its name, this is somehow related with ipv6).

So far, even systemd seems to have no problems when running without ipv6 despite the error. I am just wondering what made people (especially systemd , its ebuild maintainers and Wikis) decide to make ipv6 appear as a hard dependency? Is ipv6 used nowadays for anything else than networking (e.g. some strange loopback or whatever)?
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ulenrich
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PostPosted: Thu Sep 12, 2013 9:26 am    Post subject: Reply with quote

I think it is internal purpose related: systemd-nspawn etc...
preventing ipv6 external for example: /etc/sysctl.conf
Code:

...
net.ipv6.conf.default.disable_ipv6=0
net.ipv6.conf.lo.disable_ipv6=0
net.ipv6.conf.eth0.disable_ipv6=1
net.ipv6.conf.wlan0.disable_ipv6=1
Your interfaces might be named different ...
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mv
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PostPosted: Thu Sep 12, 2013 4:12 pm    Post subject: Reply with quote

ulenrich wrote:
I think it is internal purpose related: systemd-nspawn etc...

Why would this require IPv6?
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PostPosted: Thu Sep 12, 2013 8:33 pm    Post subject: Re: No ipv6 with systemd and others Reply with quote

Quote:
Why would somebody want to enable IPv6 support in kernel on a home system if the internet provider and local modem do not support it?


My ISP has a native IPv6 connection (as well as IPv4). I use a PPPoA <-> PPPoE bridge (as the UK is PPPoA) so I an use a NetBSD PPPoE client for IPv6.
This works very well - I assume the same is possible with a Gentoo based router.

mv wrote:
Also other programs seem to require it, e.g. dhcpcd defaults to ip4vll (despite its name, this is somehow related with ipv6).


If has zero to do with IPv6.
IPv6 gives a local link address per device.
IPv4LL is a similar concept, but for only for IPv4 and only when a DHCP or static lease is not available.

dhcpcd-6 does have IPv6 support for RA and DHCPv6 though - maybe this has confused you.

Quote:
Is ipv6 used nowadays for anything else than networking (e.g. some strange loopback or whatever)?


Is IPv4 used for anything else than networking? It's kinda of a silly question.
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mv
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PostPosted: Thu Sep 12, 2013 9:44 pm    Post subject: Re: No ipv6 with systemd and others Reply with quote

UberLord wrote:
If has zero to do with IPv6.

Thanks for clarification.
Quote:
Is IPv4 used for anything else than networking? It's kinda of a silly question.

Even if you have a machine which is not connected to any network, you need certain minimal kernel support for networking, e.g. to administer cups (even if you use only a local printer).
I was wondering whether systemd makes something similar with IPv6. systemd-nspawn was already mentioned, but I do not see the connection with IPv6.
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UberLord
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PostPosted: Thu Sep 12, 2013 11:01 pm    Post subject: Reply with quote

I doubt systemd actually uses anything specifcally IPv6.
But then, I don't have an overly high opinion of the maintainers, so who knows what they use it for.
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mv
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PostPosted: Fri Sep 13, 2013 7:47 am    Post subject: Reply with quote

UberLord wrote:
I don't have an overly high opinion of the maintainers

Neither do I; in fact, except for testing occassionally some scripts which are supposed to work with any init-systems, I do not use systemd. I was just wondering about the instructions given everywhere and the error message when you have no IPv6.
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Ant P.
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PostPosted: Fri Sep 13, 2013 3:05 pm    Post subject: Re: No ipv6 with systemd and others Reply with quote

mv wrote:
Why would somebody want to enable IPv6 support in kernel on a home system if the internet provider and local modem do not support it?

No good reason, but the link-local autoconfig is nice to have if you screw up some IPv4 config and need to ssh into a LAN server to fix it ;)
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ulenrich
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PostPosted: Sun Sep 15, 2013 9:29 am    Post subject: Reply with quote

Looking at systemd-207 README
it (only) "strongly" recommend" ipv6
Code:
REQUIREMENTS:
        Linux kernel >= 3.0
          CONFIG_DEVTMPFS
          CONFIG_CGROUPS (it's OK to disable all controllers)
          CONFIG_INOTIFY_USER
          CONFIG_SIGNALFD
          CONFIG_TIMERFD
          CONFIG_EPOLL
          CONFIG_NET
          CONFIG_SYSFS
       
        Linux kernel >= 3.8 for Smack support
       
        Udev will fail to work with the legacy layout:
          CONFIG_SYSFS_DEPRECATED=n

        Legacy hotplug slows down the system and confuses udev:
          CONFIG_UEVENT_HELPER_PATH=""

        Userspace firmware loading is deprecated, will go away, and
        sometimes causes problems:
          CONFIG_FW_LOADER_USER_HELPER=n

        Some udev rules and virtualization detection relies on it:
          CONFIG_DMIID

        Mount and bind mount handling might require it:
          CONFIG_FHANDLE

        Optional but strongly recommended:
          CONFIG_IPV6
          CONFIG_AUTOFS4_FS
          CONFIG_TMPFS_POSIX_ACL
          CONFIG_TMPFS_XATTR
          CONFIG_SECCOMP

As systemd is not only a boot-startup-init system but also wants to make sophicticated features of the Linux eco-system available to the ordinary user, I guess systemd-developers want to use that ipv6 space ...

PS: systemd-207 just lifted requirement linux-2.6.39 to kernel linux-3.0 !
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PostPosted: Sat Apr 05, 2014 7:58 pm    Post subject: Re: No ipv6 with systemd and others Reply with quote

mv wrote:
This appears like a rather stupid question:

Why would somebody want to enable IPv6 support in kernel on a home system if the internet provider and local modem do not support it?

I thought this question is stupid, since the answer should be obviously that you do not need it if you do not run an ipv6 network directly.
However, the systemd ebuild and related Wkis say that you must enable it in the kernel, systemd gives an error message when it is not enabled.
Also other programs seem to require it, e.g. dhcpcd defaults to ip4vll (despite its name, this is somehow related with ipv6).

So far, even systemd seems to have no problems when running without ipv6 despite the error. I am just wondering what made people (especially systemd , its ebuild maintainers and Wikis) decide to make ipv6 appear as a hard dependency? Is ipv6 used nowadays for anything else than networking (e.g. some strange loopback or whatever)?


I realize this is a little old, but I have to agree with the OP on this. Our new router supports IPv6 DHCP from the ISP only, i.e. the address is fetched as IPv6 but the LAN DHCP server still only hands out IPv4. As such, when I switched to systemd this weekend wicd no longer connects and
Code:
$ systemctl status network.target dhcpcd.service
shows Failed as the router's DHCP server only understands IPv4. Consequently, my ISP is still on IPv4...

An easy work around for this is to:
  1. Enable IPv6 in kernel.
  2. Switch to a profile that supports systemd , using eselect profile. This enables IPv6 and any other needed flags.
  3. Use ufed, or add -ipv6 to /etc/make.conf to effectively override systemd.
  4. emerge -uDN world


Since IPv6 is enabled in the kernel, systemd doesn't complain, about missing options, and my router is happy again with IPv4.
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Last edited by eyoung100 on Fri May 16, 2014 11:55 pm; edited 1 time in total
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TechnoMage40
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PostPosted: Wed Apr 23, 2014 5:47 pm    Post subject: Reply with quote

not that old. I was bitten by this same issue on my work Gentoo box... I first thought to force dhcpcd to use IPv4 by adding the -4 cmdline arg, but that gave me about 5-10 minutes of a working IP address, then systemd, in its "wisdom" said, 'nah, you need to be using IPv6', and everything broke again... :D

After reading this post, I used the -ipv6 USE flag and am finishing the world update as I type (I had to run it with --fetchonly so I wouldn't have the emerge process die after the network connection reset).

But at this point, I think that the processes that systemd was using to force the NIC to IPv6 have been properly updated, because it's maintained its usual v4 address for over an hour now.
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