[Bug 1094345] Re: IPv6 DHCP record is too late in resolvconf interface-order

[Thomas Hood]

Consider eth0 with inet, inet6, dhclient and ip6.dhclient records. These
are currently ordered (alphabetically) as follows.

    eth0.dhclient
    eth0.inet
    eth0.inet6
    eth0.ip6.dhclient

Observations:
* IPv4 comes before IPv6
* The prioritization of *dhclient versus inet* is inconsistent.

I propose to change the order to the following.

    eth0.inet6
    eth0.inet
    eth0.ip6.dhclient
    eth0.dhclient

That is:
* IPv6 before IPv4
* inet before dhclient

Rationale:
* NetworkManager prioritizes IPv6 before IPv4
* Putting inet before dhclient allows "dns-nameservers" to be used to override addresses of faulty nameservers coming in via DHCP

Accordingly, here is a first draft of a new factory-shipped interface-
order file.

=== BEGIN ===
# interface-order(5)
lo.inet6
lo.inet
lo.@(dnsmasq|pdnsd)
lo.!(pdns|pdns-recursor)
lo
tun*
tap*
hso*
em+([0-9])?(_+([0-9]))*
p+([0-9])p+([0-9])?(_+([0-9]))*
eth*([^.]).inet6
eth*([^.]).inet
eth*([^.]).ip6.@(dhclient|dhcpcd|pump|udhcpc)
eth*([^.]).@(dhclient|dhcpcd|pump|udhcpc)
eth*
@(ath|wifi|wlan)*([^.]).inet6
@(ath|wifi|wlan)*([^.]).inet
@(ath|wifi|wlan)*([^.]).ip6.@(dhclient|dhcpcd|pump|udhcpc)
@(ath|wifi|wlan)*([^.]).@(dhclient|dhcpcd|pump|udhcpc)
@(ath|wifi|wlan)*
ppp*
*
=== END ===

Testing this by creating a bunch of fake records in a directory...

=== BEGIN ===
# /lib/resolvconf/list-records
lo.inet6
lo.inet
lo.dnsmasq
lo.pdnsd
lo
tun0
tap0
hso0
em0_0
p0p0_0
eth0.inet6
eth0.inet
eth0.ip6.dhclient
eth0.dhclient
wlan0.inet6
wlan0.inet
ath0.ip6.dhclient
wlan0.ip6.dhclient
ath0.dhclient
wlan0.dhclient
ppp0
ppp1
=== END ===

This probably needs some more tweaking.  I am not sure what to do about
tun, tap, hso and br so I haven't changed these.  The change that
worries me the most is putting eth0.inet before eth0.dhclient whereas
currently (resolvconf 1.69 and earlier) eth0.inet comes after
eth0.dhclient. I think that the change shouldn't affect too many people
because few people have a stanza like the following.

    iface eth0 inet dhcp
        dns-nameservers 1.2.3.4    # Overridden by DHCP-provided nameserver addresses

Comments and advice are most welcome.

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https://bugs.launchpad.net/bugs/1094345

Title:
  IPv6 DHCP record is too late in resolvconf interface-order

Status in “resolvconf” package in Ubuntu:
  Confirmed

Bug description:
  I am using /etc/network/interfaces rather than NetworkManager on this
  machine. resolvconf is always writing the IPv4 nameservers and search
  domains before the IPv6. I would like the IPv6 resolver information to
  be given priority or a method to select the behavior.

  kjotte at pegasus:~$ cat /etc/network/interfaces
  # This file describes the network interfaces available on your system
  # and how to activate them. For more information, see interfaces(5).

  # The loopback network interface
  auto lo
  iface lo inet loopback

  # The primary network interface
  auto eth0
  iface eth0 inet6 auto
      dhcp 1
  iface eth0 inet dhcp

  kjotte at pegasus:~$ cat /etc/resolv.conf 
  # Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
  #     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
  nameserver 172.31.3.4
  nameserver 2001:470:8:64f::4
  search nivex.lan home.nivex.net

  ProblemType: Bug
  DistroRelease: Ubuntu 12.10
  Package: resolvconf 1.67ubuntu2
  ProcVersionSignature: Ubuntu 3.5.0-21.32-generic 3.5.7.1
  Uname: Linux 3.5.0-21-generic i686
  NonfreeKernelModules: nvidia
  ApportVersion: 2.6.1-0ubuntu6
  Architecture: i386
  Date: Fri Dec 28 15:33:41 2012
  MarkForUpload: True
  PackageArchitecture: all
  SourcePackage: resolvconf
  UpgradeStatus: Upgraded to quantal on 2012-05-10 (232 days ago)

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