Public bug reported:
Summary:
========
If a interface does not yet have a link-local address (as it may have
just been brought up), dhclient -6 <ifname> will fail. The built-in
"wait for link-local address" loop does not function properly, causing
DHCP failure.
Discussion:
===========
In trying to configure isc-dhcp-client 4.3.5-3ubuntu1 for IPv6 on Ubuntu
17.04, I was finding that on boot I was getting failures with the logged
message "no link-local IPv6 address for <ifname>"
I found that it took several seconds for the link-local address to be
assigned when the interface came up (in this case, the ISP/modem-facing
interface), and worked around it with a script that looks at
/sbin/ifconfig $IFACE | /bin/fgrep -q 'scopeid 0x20'
and loops for a fixed number of times for that to be successful.
On looking at /sbin/dhclient-script it appears that it *tries* to do the
same thing in
# set the link up and wait for ipv6 link local dad to finish
ipv6_link_up_and_dad()
this code sets
out=$(ip -6 -o address show dev "$dev" scope link)
then checks it with a case statement inside of a loop for
case " $out " in
*\ dadfailed\ *)
error "$dev: ipv6 dad failed."
return 1;;
*\ tentative\ *) :;;
*) return 0;;
esac
If there is no link-local address, $out will be empty. The default case
is taken, and the loop exits immediately:
$ echo "'$out'" ; case " $out " in
> *\ dadfailed\ *)
> echo "dadfailed"
> ;;
> *\ tentative\ *)
> echo "tentative"
> ;;
> *)
> echo "default"
> esac
''
default
As a result, there is no "wait for link-local address" and when there is
no link-local address, dhclient fails later on.
Possible Fix:
=============
Adding "the missing case" for "no address" case that continues the loop
is one possible solution.
case " $out " in
*\ dadfailed\ *)
error "$dev: ipv6 dad failed."
return 1;;
*\ tentative\ *) :;;
" ")
:
;;
*) return 0;;
esac
At least in my situation, this prevents the failure of dhclient due to
the link-local address not being "ready" yet.
** Affects: isc-dhcp (Ubuntu)
Importance: Undecided
Status: New
** Affects: isc-dhcp (Debian)
Importance: Unknown
Status: Unknown
** Tags: ipv6
** Description changed:
Summary:
========
- If a interface does not have a link-local address, dhclient -6 <ifname>
- will fail. The built-in "wait for link-local address" loop does not
- function properly, causing DHCP failure.
+ If a interface does not yet have a link-local address (as it may have
+ just been brought up), dhclient -6 <ifname> will fail. The built-in
+ "wait for link-local address" loop does not function properly, causing
+ DHCP failure.
Discussion:
===========
In trying to configure isc-dhcp-client 4.3.5-3ubuntu1 for IPv6 on Ubuntu
17.04, I was finding that on boot I was getting failures with the logged
message "no link-local IPv6 address for <ifname>"
I found that it took several seconds for the link-local address to be
assigned when the interface came up (in this case, the ISP/modem-facing
interface), and worked around it with a script that looks at
- /sbin/ifconfig $IFACE | /bin/fgrep -q 'scopeid 0x20'
+ /sbin/ifconfig $IFACE | /bin/fgrep -q 'scopeid 0x20'
and loops for a fixed number of times for that to be successful.
On looking at /sbin/dhclient-script it appears that it *tries* to do the
same thing in
- # set the link up and wait for ipv6 link local dad to finish
- ipv6_link_up_and_dad()
+ # set the link up and wait for ipv6 link local dad to finish
+ ipv6_link_up_and_dad()
this code sets
- out=$(ip -6 -o address show dev "$dev" scope link)
+ out=$(ip -6 -o address show dev "$dev" scope link)
then checks it with a case statement inside of a loop for
- case " $out " in
- *\ dadfailed\ *)
- error "$dev: ipv6 dad failed."
- return 1;;
- *\ tentative\ *) :;;
- *) return 0;;
- esac
+ case " $out " in
+ *\ dadfailed\ *)
+ error "$dev: ipv6 dad failed."
+ return 1;;
+ *\ tentative\ *) :;;
+ *) return 0;;
+ esac
If there is no link-local address, $out will be empty. The default case
is taken, and the loop exits immediately:
$ echo "'$out'" ; case " $out " in
> *\ dadfailed\ *)
> echo "dadfailed"
> ;;
> *\ tentative\ *)
> echo "tentative"
> ;;
> *)
> echo "default"
> esac
''
default
As a result, there is no "wait for link-local address" and when there is
no link-local address, dhclient fails later on.
-
Possible Fix:
=============
Adding "the missing case" for "no address" case that continues the loop
is one possible solution.
- case " $out " in
- *\ dadfailed\ *)
- error "$dev: ipv6 dad failed."
- return 1;;
- *\ tentative\ *) :;;
- " ")
- :
- ;;
- *) return 0;;
- esac
+ case " $out " in
+ *\ dadfailed\ *)
+ error "$dev: ipv6 dad failed."
+ return 1;;
+ *\ tentative\ *) :;;
+ " ")
+ :
+ ;;
+ *) return 0;;
+ esac
At least in my situation, this prevents the failure of dhclient due to
the link-local address not being "ready" yet.
** Bug watch added: Debian Bug tracker #783387
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=783387
** Also affects: isc-dhcp (Debian) via
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=783387
Importance: Unknown
Status: Unknown
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https://bugs.launchpad.net/bugs/1718568
Title:
dhclient-script fails to wait for link-local address
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