I've noticed strange behavior on one of my machines with Linux 4.8.0 (Debian Sid)
My ISPs router is sending IPv6 RAs as following:
IP6 (hlim 255, next-header ICMPv6 (58) payload length: 128) fe80::5667:51ff:fee7:7cf > ff02::1: [icmp6 sum ok] ICMP6, router advertisement, length 128
hop limit 64, Flags [other stateful], pref high, router lifetime 180s, reachable time 0s, retrans time 0s
prefix info option (3), length 32 (4): <prefix>::/64, Flags [onlink, auto], valid time 1138201s, pref. time 533401s
route info option (24), length 24 (3): <prefix>::/64, pref=medium, lifetime=1143629s
rdnss option (25), length 40 (5): lifetime 360s, addr: <dns1> addr: <dns2>
mtu option (5), length 8 (1): 1500
source link-address option (1), length 8 (1): 54:67:51:e7:07:cf
This results in following routing table:
ip -6 r
<prefix>::/64 via fe80::5667:51ff:fee7:7cf dev eth0 proto ra metric 100 pref medium
fe80::5667:51ff:fee7:7cf dev eth0 proto static metric 100 pref medium
fe80::/64 dev eth0 proto kernel metric 256 pref medium
default via fe80::5667:51ff:fee7:7cf dev eth0 proto static metric 100 pref medium
First entry is odd. All local subnet traffic is being forwarded via router which isn't very optimal. Also I have accept_ra_rt_info_max_plen set to 0.
On my other machine in the same subnet with Linux 4.7.0 (Debian Jessie) routing table looks like expected:
<prefix>::/64 dev eth0 proto kernel metric 256 expires 1136467sec
fe80::/64 dev eth0 proto kernel metric 256
default via fe80::5667:51ff:fee7:7cf dev eth0 proto ra metric 1024 expires 120sec hoplimit 64
What can be the reason for this behavior? How can I modify my config so traffic towards local subnet is not send via router?