[pkg-dhcp-devel] Bug#684009: isc-dhcp-client: dhclient must not assume a IPv6 prefix length of 64 when setting an address

[Arne Nordmark]

Package: isc-dhcp-client
Version: 4.2.2.dfsg.1-5
Severity: normal
Tags: upstream ipv6 patch

dhclient unconditionally assumes an on-link prefix matching the address 
and with a length of 64 when setting an IPv6 address. Like routing 
information, on-link prefix information is not part of the DHCPv6 
protocol, so this is just a guess from the part of dhclient.

RFC 5942 asserts that on-link prefixes and addresses are independent 
concepts, and on-link prefix information must only come from Router 
Advertisements or manual configuration. Section 5 specifically points 
out that a /64 prefix must not be assumed.

In my case where a /112 prefix is used, the routing table becomes

nordmark at strix:~$ ip -6 route
2001:6b0:1:1e90::40:0/112 dev wlan0  proto kernel  metric 256  expires 
2592301sec
2001:6b0:1:1e90::/64 dev wlan0  proto kernel  metric 256
default via fe80::92e6:baff:fe68:ce8f dev wlan0  proto kernel  metric 
1024 expires 1777sec

and hosts sharing the /64 prefix but not the /112 are falsely determined 
as being on-link, and have become unreachable.

This is (probably, the bug tracking is closed so I can not verify) 
reported upstream as ISC-Bugs #29468.

The corresponding bug where Network Manager wrongly trusts the prefix 
length information from dhclient is #661885.

The incuded patch removes the use of the bogus ip6_prefixlen variables 
from dhclient-script and uses /128 when setting an address. Should other 
programs use these variables, they are hard coded as 128 instead of 64.

Arne


-- System Information:
Debian Release: wheezy/sid
   APT prefers testing
   APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.0-3-amd64 (SMP w/4 CPU cores)
Locale: LANG=sv_SE.UTF-8, LC_CTYPE=sv_SE.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages isc-dhcp-client depends on:
ii  debianutils      4.3.2
ii  iproute          20120521-3
ii  isc-dhcp-common  4.2.2.dfsg.1-5
ii  libc6            2.13-33

isc-dhcp-client recommends no packages.

Versions of packages isc-dhcp-client suggests:
ii  avahi-autoipd  0.6.31-1
ii  resolvconf     1.67

-- no debconf information
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