Confirmed that the same apparent flaw in dhclient-script appears to exist in 4.3.3-5ubuntu12.7 under Ubuntu 16.04.3 LTS
This appears related to / caused by LP: #1633479 based on http://launchpadlibrarian.net/291516262/isc-dhcp_4.3.3-5ubuntu15_4.3.3-5ubuntu15.1.diff.gz ** Description changed: 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. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1718568 Title: dhclient-script fails to wait for link-local address To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1718568/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
