kern/55091: IPv6 default route selection fails to harmonize automatically

[kim%netbsd.org@localhost (Kimmo Suominen)]

>Number:         55091
>Category:       kern
>Synopsis:       IPv6 default route selection fails to harmonize automatically
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Mar 20 12:55:00 +0000 2020
>Originator:     Kimmo Suominen
>Release:        NetBSD 9.0
>Organization:
>Environment:
System: NetBSD oxygene.gw.com 9.0 NetBSD 9.0 (GENERIC) #0: Fri Feb 14 00:06:28 UTC 2020 mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:

On a network segment with multiple routers advertising the default
route using IPv6 router advertisements, the NetBSD kernel fails to
install the highest priority route in the routing table, even over
time.

Running "ndp -H" results in the expected default being installed
in the kernel routing table correctly.

>How-To-Repeat:

# ndp -r
fe80::f29f:c2ff:fe12:1047%vioif0 if=vioif0, flags=, pref=high, expire=26m26s
fe80::de9f:dbff:fe28:887f%vioif0 if=vioif0, flags=, pref=medium, expire=29m48s

# netstat -rnf inet6 | awk '$1 == "default" {print}'
default fe80::de9f:dbff:fe28:887f UG - - - vioif0

# ndp -H
# netstat -rnf inet6 | awk '$1 == "default" {print}'
default fe80::f29f:c2ff:fe12:1047 UG - - - vioif0

# ndp -i vioif0
linkmtu=0, maxmtu=1500, curhlim=64, basereachable=30s0ms, reachable=15s, retrans=1s0ms
Flags: nud accept_rtadv auto_linklocal

>Fix: