Comment 0 for bug 1510098

After installing 15.10 ipv6 gateway not set on start up. In 15.04 it did worked fine

andrej@nikel:~$ cat /etc/network/interfaces
auto lo enp4s0

iface lo inet loopback
iface enp4s0 inet manual
iface enp4s0 inet6 static
  address ----:200:8221::---
  netmask 64
  gateway ----198:20-----

andrej@nikel:~$ ip -6 route
2a01:198:200:8221::/64 dev enp4s0 proto kernel metric 256 mtu 1500 pref medium
fe80::/64 dev enp4s0 proto kernel metric 256 mtu 1500 pref medium
fe80::/64 dev lxcbr0 proto kernel metric 256 pref medium
fe80::/64 dev docker0 proto kernel metric 256 pref medium

3: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 00:15:17:9e:b7:98 brd ff:ff:ff:ff:ff:ff
    inet 10.0.4.1/8 brd 10.255.255.255 scope global enp4s0
       valid_lft forever preferred_lft forever
    inet6 2a01:198:200:8221::756/64 scope global
       valid_lft forever preferred_lft forever
    inet6 2a01:198:200:8221:215:17ff:fe9e:b798/64 scope global mngtmpaddr dynamic
       valid_lft 83024sec preferred_lft 11024sec
    inet6 fe80::215:17ff:fe9e:b798/64 scope link
       valid_lft forever preferred_lft forever

andrej@nikel:~$ cat /etc/sysctl.conf
net.ipv4.conf.default.rp_filter= 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.tcp_syncookies = 1

net.ipv6.conf.all.use_tempaddr = 2
net.ipv6.conf.default.use_tempaddr = 2
net.ipv6.conf.enp4s0.use_tempaddr = 2

andrej@nikel:/proc/sys/net/ipv6/conf/enp4s0$ for i in *; do echo -n "$i: " ; cat $i ; done
accept_dad: 1
accept_ra: 0
accept_ra_defrtr: 1
accept_ra_from_local: 0
accept_ra_mtu: 1
accept_ra_pinfo: 1
accept_ra_rt_info_max_plen: 0
accept_ra_rtr_pref: 1
accept_redirects: 1
accept_source_route: 0
autoconf: 0
dad_transmits: 1
disable_ipv6: 0
force_mld_version: 0
force_tllao: 0
forwarding: 0
hop_limit: 64
max_addresses: 16
max_desync_factor: 600
mc_forwarding: 0
mldv1_unsolicited_report_interval: 10000
mldv2_unsolicited_report_interval: 1000
mtu: 1500
ndisc_notify: 0
proxy_ndp: 0
regen_max_retry: 3
router_probe_interval: 60
router_solicitation_delay: 1
router_solicitation_interval: 4
router_solicitations: 3
cat: stable_secret: Permission denied
stable_secret: suppress_frag_ndisc: 1
temp_prefered_lft: 86400
temp_valid_lft: 604800
use_tempaddr: 2

Maybe related: https://bugs.launchpad.net/ubuntu/+source/miredo/+bug/1510047

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ifupdown 0.7.54ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.1-0ubuntu3
Architecture: amd64
Date: Mon Oct 26 14:41:55 2015
JournalErrors:
 No journal files were found.
 -- No entries --
SourcePackage: ifupdown
UpgradeStatus: No upgrade log present (probably fresh install)