| 2017-09-21 03:19:46 |
Jeff |
bug |
|
|
added bug |
| 2017-09-21 03:23:50 |
Jeff |
description |
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.
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. |
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. |
|
| 2017-09-21 03:26:36 |
Jeff |
bug watch added |
|
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=783387 |
|
| 2017-09-21 03:26:36 |
Jeff |
bug task added |
|
isc-dhcp (Debian) |
|
| 2017-09-21 03:49:01 |
Jeff |
description |
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. |
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. |
|
| 2017-09-21 04:07:58 |
Jeff |
attachment added |
|
Patch to detect no link-local address https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/4954114/+files/dhclient-script.diff |
|
| 2017-09-21 04:09:17 |
Jeff |
description |
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. |
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. |
|
| 2017-09-21 04:18:58 |
Ubuntu Foundations Team Bug Bot |
tags |
ipv6 |
ipv6 patch |
|
| 2017-09-21 04:19:05 |
Ubuntu Foundations Team Bug Bot |
bug |
|
|
added subscriber Ubuntu Review Team |
| 2017-09-21 13:15:59 |
Bug Watch Updater |
isc-dhcp (Debian): status |
Unknown |
New |
|
| 2017-09-21 15:43:32 |
Dan Streetman |
bug |
|
|
added subscriber Dan Streetman |
| 2017-10-12 11:24:23 |
Dan Streetman |
nominated for series |
|
Ubuntu Artful |
|
| 2017-10-12 11:24:23 |
Dan Streetman |
nominated for series |
|
Ubuntu Trusty |
|
| 2017-10-12 11:24:23 |
Dan Streetman |
nominated for series |
|
Ubuntu Zesty |
|
| 2017-10-12 11:24:23 |
Dan Streetman |
nominated for series |
|
Ubuntu Xenial |
|
| 2017-10-12 11:48:16 |
Eric Desrochers |
bug task added |
|
isc-dhcp (Ubuntu Artful) |
|
| 2017-10-12 11:48:20 |
Eric Desrochers |
bug task added |
|
isc-dhcp (Ubuntu Trusty) |
|
| 2017-10-12 11:48:26 |
Eric Desrochers |
bug task added |
|
isc-dhcp (Ubuntu Xenial) |
|
| 2017-10-12 11:48:31 |
Eric Desrochers |
bug task added |
|
isc-dhcp (Ubuntu Zesty) |
|
| 2017-10-12 12:19:23 |
Dan Streetman |
isc-dhcp (Ubuntu Trusty): assignee |
|
Dan Streetman (ddstreet) |
|
| 2017-10-12 12:19:24 |
Dan Streetman |
isc-dhcp (Ubuntu Xenial): assignee |
|
Dan Streetman (ddstreet) |
|
| 2017-10-12 12:19:26 |
Dan Streetman |
isc-dhcp (Ubuntu Zesty): assignee |
|
Dan Streetman (ddstreet) |
|
| 2017-10-12 12:19:28 |
Dan Streetman |
isc-dhcp (Ubuntu Artful): assignee |
|
Dan Streetman (ddstreet) |
|
| 2017-10-12 12:19:31 |
Dan Streetman |
isc-dhcp (Ubuntu Artful): importance |
Undecided |
Medium |
|
| 2017-10-12 12:19:34 |
Dan Streetman |
isc-dhcp (Ubuntu Zesty): importance |
Undecided |
Medium |
|
| 2017-10-12 12:19:36 |
Dan Streetman |
isc-dhcp (Ubuntu Trusty): importance |
Undecided |
Medium |
|
| 2017-10-12 12:19:38 |
Dan Streetman |
isc-dhcp (Ubuntu Xenial): importance |
Undecided |
Medium |
|
| 2017-10-12 12:19:39 |
Dan Streetman |
isc-dhcp (Ubuntu Artful): status |
New |
In Progress |
|
| 2017-10-12 12:19:41 |
Dan Streetman |
isc-dhcp (Ubuntu Zesty): status |
New |
In Progress |
|
| 2017-10-12 12:19:42 |
Dan Streetman |
isc-dhcp (Ubuntu Xenial): status |
New |
In Progress |
|
| 2017-10-12 12:19:44 |
Dan Streetman |
isc-dhcp (Ubuntu Trusty): status |
New |
In Progress |
|
| 2017-10-12 13:28:52 |
Dan Streetman |
attachment added |
|
lp1718568-artful.debdiff https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/4968656/+files/lp1718568-artful.debdiff |
|
| 2017-10-12 13:29:07 |
Dan Streetman |
attachment added |
|
lp1718568-zesty.debdiff https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/4968657/+files/lp1718568-zesty.debdiff |
|
| 2017-10-12 13:29:22 |
Dan Streetman |
attachment added |
|
lp1718568-xenial.debdiff https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/4968658/+files/lp1718568-xenial.debdiff |
|
| 2017-10-12 13:29:38 |
Dan Streetman |
attachment added |
|
lp1718568-trusty.debdiff https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/4968659/+files/lp1718568-trusty.debdiff |
|
| 2017-10-12 13:40:14 |
Dan Streetman |
description |
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. |
[impact]
bug 1633479 made a change to isc-dhcp to wait for an interface's link-local ipv6 address to switch from 'tentative' to normal, because all link-local addresses briefly go through a 'tentative' state while the kernel is performing ipv6 link-local 'duplicate address detection' (DAD). While in the 'tentative' state, dhclient can't take over the interface and send out
dhcpv6 requests; it must wait until DAD completes.
However, the change made in that bug does not account for the case where the 'tentative' check is done before the interface has even set up a link-local address; its case statement assumes if there is no 'tentative' or 'dadfailed' string in the output, the link-local address is ready to use. When the address check finds no address at all, this will return as successful, even though it shouldn't, and dhclient will fail to get the dhcpv6 address.
[test case]
on a system that is configured for dhcpv6 on one or more of its interfaces, repeatedly try to get the dhcpv6 address. For interfaces that are slower to actually set up their initial tentative link-local address, they will occasionally fail, since the current code is a race between the kernel adding the tentative link-local address, and the dhclient-script.linux code checking the interface for a tentative address.
with the patch to correct this, even interfaces slow to add their tentative link-local address should correctly wait for the address to get added, and then transition from tentative to normal, and then begin the dhcpv6 process.
[regression potential]
errors in this function can cause dhclient to fail to get a ipv6 address for an interface; regression would happen if this patch makes it fail more than it already is failing, but would not cause other failures or problems after getting an ipv6 address; this patch will affect only startup-time.
[other info]
related bug 1633479
[original description]
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. |
|
| 2017-10-12 13:44:41 |
Dan Streetman |
nominated for series |
|
Ubuntu Bb-series |
|
| 2017-10-12 13:47:00 |
Eric Desrochers |
bug task added |
|
isc-dhcp (Ubuntu Bb-series) |
|
| 2017-10-12 13:47:13 |
Dan Streetman |
isc-dhcp (Ubuntu Bb-series): status |
New |
In Progress |
|
| 2017-10-12 13:47:15 |
Dan Streetman |
isc-dhcp (Ubuntu Bb-series): importance |
Undecided |
Medium |
|
| 2017-10-12 13:47:18 |
Dan Streetman |
isc-dhcp (Ubuntu Bb-series): assignee |
|
Dan Streetman (ddstreet) |
|
| 2018-02-16 20:27:56 |
Dan Streetman |
isc-dhcp (Ubuntu Zesty): status |
In Progress |
Won't Fix |
|
| 2018-02-20 16:47:53 |
Dan Streetman |
attachment added |
|
lp1718568-bionic.debdiff https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+attachment/5059088/+files/lp1718568-bionic.debdiff |
|
| 2018-02-20 18:01:11 |
Dan Streetman |
bug |
|
|
added subscriber Ubuntu Sponsors Team |
| 2018-02-23 18:21:23 |
Launchpad Janitor |
isc-dhcp (Ubuntu Bionic): status |
In Progress |
Fix Released |
|
| 2018-02-27 17:14:12 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Artful): status |
In Progress |
Fix Committed |
|
| 2018-02-27 17:14:15 |
Łukasz Zemczak |
bug |
|
|
added subscriber Ubuntu Stable Release Updates Team |
| 2018-02-27 17:14:17 |
Łukasz Zemczak |
bug |
|
|
added subscriber SRU Verification |
| 2018-02-27 17:14:22 |
Łukasz Zemczak |
tags |
ipv6 patch |
ipv6 patch verification-needed verification-needed-artful |
|
| 2018-02-27 17:17:17 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Xenial): status |
In Progress |
Fix Committed |
|
| 2018-02-27 17:17:25 |
Łukasz Zemczak |
tags |
ipv6 patch verification-needed verification-needed-artful |
ipv6 patch verification-needed verification-needed-artful verification-needed-xenial |
|
| 2018-02-27 17:19:01 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Trusty): status |
In Progress |
Fix Committed |
|
| 2018-02-27 17:19:09 |
Łukasz Zemczak |
tags |
ipv6 patch verification-needed verification-needed-artful verification-needed-xenial |
ipv6 patch verification-needed verification-needed-artful verification-needed-trusty verification-needed-xenial |
|
| 2018-02-27 17:19:14 |
Łukasz Zemczak |
removed subscriber Ubuntu Sponsors Team |
|
|
|
| 2018-03-01 22:40:04 |
Dan Streetman |
tags |
ipv6 patch verification-needed verification-needed-artful verification-needed-trusty verification-needed-xenial |
ipv6 patch |
|
| 2018-03-01 22:40:10 |
Dan Streetman |
isc-dhcp (Ubuntu Artful): status |
Fix Committed |
In Progress |
|
| 2018-03-01 22:40:12 |
Dan Streetman |
isc-dhcp (Ubuntu Xenial): status |
Fix Committed |
In Progress |
|
| 2018-03-01 22:40:15 |
Dan Streetman |
isc-dhcp (Ubuntu Trusty): status |
Fix Committed |
In Progress |
|
| 2018-03-02 20:14:54 |
Dan Streetman |
description |
[impact]
bug 1633479 made a change to isc-dhcp to wait for an interface's link-local ipv6 address to switch from 'tentative' to normal, because all link-local addresses briefly go through a 'tentative' state while the kernel is performing ipv6 link-local 'duplicate address detection' (DAD). While in the 'tentative' state, dhclient can't take over the interface and send out
dhcpv6 requests; it must wait until DAD completes.
However, the change made in that bug does not account for the case where the 'tentative' check is done before the interface has even set up a link-local address; its case statement assumes if there is no 'tentative' or 'dadfailed' string in the output, the link-local address is ready to use. When the address check finds no address at all, this will return as successful, even though it shouldn't, and dhclient will fail to get the dhcpv6 address.
[test case]
on a system that is configured for dhcpv6 on one or more of its interfaces, repeatedly try to get the dhcpv6 address. For interfaces that are slower to actually set up their initial tentative link-local address, they will occasionally fail, since the current code is a race between the kernel adding the tentative link-local address, and the dhclient-script.linux code checking the interface for a tentative address.
with the patch to correct this, even interfaces slow to add their tentative link-local address should correctly wait for the address to get added, and then transition from tentative to normal, and then begin the dhcpv6 process.
[regression potential]
errors in this function can cause dhclient to fail to get a ipv6 address for an interface; regression would happen if this patch makes it fail more than it already is failing, but would not cause other failures or problems after getting an ipv6 address; this patch will affect only startup-time.
[other info]
related bug 1633479
[original description]
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. |
[impact]
bug 1633479 made a change to isc-dhcp to wait for an interface's link-local ipv6 address to switch from 'tentative' to normal, because all link-local addresses briefly go through a 'tentative' state while the kernel is performing ipv6 link-local 'duplicate address detection' (DAD). While in the 'tentative' state, dhclient can't take over the interface and send out
dhcpv6 requests; it must wait until DAD completes.
However, the change made in that bug does not account for the case where the 'tentative' check is done before the interface has even set up a link-local address; its case statement assumes if there is no 'tentative' or 'dadfailed' string in the output, the link-local address is ready to use. When the address check finds no address at all, this will return as successful, even though it shouldn't, and dhclient will fail to get the dhcpv6 address.
[test case]
on a system that is configured for dhcpv6 on one or more of its interfaces, repeatedly try to get the dhcpv6 address. For interfaces that are slower to actually set up their initial tentative link-local address, they will occasionally fail, since the current code is a race between the kernel adding the tentative link-local address, and the dhclient-script.linux code checking the interface for a tentative address.
with the patch to correct this, even interfaces slow to add their tentative link-local address should correctly wait for the address to get added, and then transition from tentative to normal, and then begin the dhcpv6 process.
[regression potential]
errors in this function can cause dhclient to fail to get a ipv6 address for an interface; regression would happen if this patch makes it fail more than it already is failing, but would not cause other failures or problems after getting an ipv6 address; this patch will affect only startup-time.
additionally, the current behavior of dhclient when using an interface that has no link-local address after being brought up is to exit immediately; while after this patch dhclient will wait ~6 seconds before exiting (while waiting for the interface to get a non-tentative link-local addr). This is the point of this bug, that some NIC hw doesn't show a tentative link-local addr immediately after coming up. However, if dhclient -6 is configured to run on an interface without any link state at all (e.g. its physical cable is unplugged), then while before dhclient would exit immediately with error, it now waits 6 seconds. If the system is misconfigured like that, or if someone pulls a cable and reboots, then system boot will be delayed an extra 6 seconds. However, that short delay for misconfigured/broken systems seems acceptable to me, in exchange for allowing dhclient to work with slightly slow NIC hw. Additionally, consider that if the problem is instead no dhcpv6 server, dhclient -6 will wait a much, much longer amount of time for a dhcpv6 response before giving up.
[other info]
related bug 1633479
[original description]
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. |
|
| 2018-03-05 12:11:49 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Artful): status |
In Progress |
Fix Committed |
|
| 2018-03-05 12:11:54 |
Łukasz Zemczak |
tags |
ipv6 patch |
ipv6 patch verification-needed verification-needed-artful |
|
| 2018-03-05 12:15:31 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Xenial): status |
In Progress |
Fix Committed |
|
| 2018-03-05 12:15:36 |
Łukasz Zemczak |
tags |
ipv6 patch verification-needed verification-needed-artful |
ipv6 patch verification-needed verification-needed-artful verification-needed-xenial |
|
| 2018-03-05 12:16:30 |
Łukasz Zemczak |
isc-dhcp (Ubuntu Trusty): status |
In Progress |
Fix Committed |
|
| 2018-03-05 12:16:36 |
Łukasz Zemczak |
tags |
ipv6 patch verification-needed verification-needed-artful verification-needed-xenial |
ipv6 patch verification-needed verification-needed-artful verification-needed-trusty verification-needed-xenial |
|
| 2018-03-08 19:11:56 |
Dan Streetman |
tags |
ipv6 patch verification-needed verification-needed-artful verification-needed-trusty verification-needed-xenial |
ipv6 patch verification-done verification-done-artful verification-done-trusty verification-done-xenial |
|
| 2018-03-15 08:25:38 |
Launchpad Janitor |
isc-dhcp (Ubuntu Artful): status |
Fix Committed |
Fix Released |
|
| 2018-03-15 08:25:44 |
Łukasz Zemczak |
removed subscriber Ubuntu Stable Release Updates Team |
|
|
|
| 2018-03-15 08:30:17 |
Launchpad Janitor |
isc-dhcp (Ubuntu Xenial): status |
Fix Committed |
Fix Released |
|
| 2018-03-15 08:32:12 |
Launchpad Janitor |
isc-dhcp (Ubuntu Trusty): status |
Fix Committed |
Fix Released |
|
