On 1/19/21 2:29 PM, Praveen Chaudhary wrote: > For IPv4, default route is learned via DHCPv4 and user is allowed to change > metric using config etc/network/interfaces. But for IPv6, default route can > be learned via RA, for which, currently a fixed metric value 1024 is used. > > Ideally, user should be able to configure metric on default route for IPv6 > similar to IPv4. This fix adds sysctl for the same. > > Signed-off-by: Praveen Chaudhary <pchaudhary@xxxxxxxxxxxx> > Signed-off-by: Zhenggen Xu <zxu@xxxxxxxxxxxx> > > Changes in v1. > 1.) Correct the call to rt6_add_dflt_router. > > Changes in v2. > 1.) Replace accept_ra_defrtr_metric to ra_defrtr_metric. > 2.) Change Type to __u32 instead of __s32. > 3.) Change description in Documentation/networking/ip-sysctl.rst. > 4.) Use proc_douintvec instead of proc_dointvec. > 5.) Code style in ndisc_router_discovery(). > 6.) Change Type to u32 instead of unsigned int. > > Changes in v3: > 1.) Removed '---' and '```' from description. > 2.) Remove stray ' after accept_ra_defrtr. > 3.) Fix tab in net/ipv6/addrconf.c. > > Logs: > > For IPv4: > > Config in etc/network/interfaces: > auto eth0 > iface eth0 inet dhcp > metric 4261413864 > > IPv4 Kernel Route Table: > $ ip route list > default via 172.21.47.1 dev eth0 metric 4261413864 > > FRR Table, if a static route is configured: > [In real scenario, it is useful to prefer BGP learned default route over DHCPv4 default route.] > Codes: K - kernel route, C - connected, S - static, R - RIP, > O - OSPF, I - IS-IS, B - BGP, P - PIM, E - EIGRP, N - NHRP, > T - Table, v - VNC, V - VNC-Direct, A - Babel, D - SHARP, > > - selected route, * - FIB route > > S>* 0.0.0.0/0 [20/0] is directly connected, eth0, 00:00:03 > K 0.0.0.0/0 [254/1000] via 172.21.47.1, eth0, 6d08h51m > > i.e. User can prefer Default Router learned via Routing Protocol in IPv4. > Similar behavior is not possible for IPv6, without this fix. > > After fix [for IPv6]: > sudo sysctl -w net.ipv6.conf.eth0.net.ipv6.conf.eth0.ra_defrtr_metric=1996489705 > > IP monitor: [When IPv6 RA is received] > default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489705 pref high > > Kernel IPv6 routing table > $ ip -6 route list > default via fe80::be16:65ff:feb3:ce8e dev eth0 proto ra metric 1996489705 expires 21sec hoplimit 64 pref high > > FRR Table, if a static route is configured: > [In real scenario, it is useful to prefer BGP learned default route over IPv6 RA default route.] > Codes: K - kernel route, C - connected, S - static, R - RIPng, > O - OSPFv3, I - IS-IS, B - BGP, N - NHRP, T - Table, > v - VNC, V - VNC-Direct, A - Babel, D - SHARP, > > - selected route, * - FIB route > > S>* ::/0 [20/0] is directly connected, eth0, 00:00:06 > K ::/0 [119/1001] via fe80::xx16:xxxx:feb3:ce8e, eth0, 6d07h43m > > If the metric is changed later, the effect will be seen only when next IPv6 > RA is received, because the default route must be fully controlled by RA msg. > Below metric is changed from 1996489705 to 1996489704. > > $ sudo sysctl -w net.ipv6.conf.eth0.ra_defrtr_metric=1996489704 > net.ipv6.conf.eth0.ra_defrtr_metric = 1996489704 > > IP monitor: > [On next IPv6 RA msg, Kernel deletes prev route and installs new route with updated metric] > > Deleted default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489705 expires 3sec hoplimit 64 pref high > default via fe80::xx16:xxxx:feb3:ce8e dev eth0 proto ra metric 1996489704 pref high > --- > Documentation/networking/ip-sysctl.rst | 12 ++++++++++++ > include/linux/ipv6.h | 1 + > include/net/ip6_route.h | 3 ++- > include/uapi/linux/ipv6.h | 1 + > include/uapi/linux/sysctl.h | 1 + > net/ipv6/addrconf.c | 10 ++++++++++ > net/ipv6/ndisc.c | 14 ++++++++++---- > net/ipv6/route.c | 5 +++-- > 8 files changed, 40 insertions(+), 7 deletions(-) > LGTM. I can't think of a better way to do this than a sysctl. Shame that the metric/priority is not an RA option. Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
