[Bug 1632096] Re: dhclient-script does not respect ip6_prefixlen

[LaMont Jones]

*** This bug is a duplicate of bug 1609898 ***
    https://bugs.launchpad.net/bugs/1609898

The DHCP v6 protocol does not include prefixlen: On-link indication
comes from router-advertisements, only.

So it's not so much that the script is ignoring it, as it is that
dhclient is making up answers.

** This bug has been marked a duplicate of bug 1609898
   dhclient incorrectly assumes a /64 ipv6 prefix

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https://bugs.launchpad.net/bugs/1632096

Title:
  dhclient-script does not respect ip6_prefixlen

Status in isc-dhcp package in Ubuntu:
  New

Bug description:
  /sbin/dhclient-script does not seem to pay any attention to the prefixlen that is provided.
  The result is that:
  $ dhclient -6 -1 -v eth0
  results in network configuration like this:

  
  2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast qlen 1000
      link/ether 52:54:00:12:34:56 brd ff:ff:ff:ff:ff:ff
      inet6 fd42:83bb:a360:8010:2527:abdf:95cb:5e55/128 scope global 
         valid_lft forever preferred_lft forever
      inet6 fe80::5054:ff:fe12:3456/64 scope link 
         valid_lft forever preferred_lft forever

  when it should have a /64 on the fd42 address, and subsequently no
  ability to reach other hosts on that network.

  The fix seems simple enough:
    ip -6 addr add ${new_ip6_address}${new_ip6_prefixlen:+/${new_ip6_prefixlen}}
       dev ${interface} scope global

  Ie, we just have to add '/${new_ip6_prefixlen}' if it is set.

  
  This link seems relevant:

  https://kb.isc.org/article/AA-01141/0/How-to-workaround-IPv6-prefix-
  length-issues-with-ISC-DHCP-clients.html

  ProblemType: Bug
  DistroRelease: Ubuntu 16.10
  Package: isc-dhcp-client 4.3.3-5ubuntu15
  ProcVersionSignature: Ubuntu 4.8.0-17.19-generic 4.8.0-rc7
  Uname: Linux 4.8.0-17-generic x86_64
  NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
  ApportVersion: 2.20.3-0ubuntu7
  Architecture: amd64
  Date: Mon Oct 10 20:23:42 2016
  DhclientLeases:
   
  JournalErrors:
   Error: command ['journalctl', '-b', '--priority=warning', '--lines=1000'] failed with exit code 1: Hint: You are currently not seeing messages from other users and the system.
         Users in the 'systemd-journal' group can see all messages. Pass -q to
         turn off this notice.
   No journal files were opened due to insufficient permissions.
  ProcEnviron:
   TERM=screen-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: isc-dhcp
  UpgradeStatus: No upgrade log present (probably fresh install)

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