Date: Wed, 17 Jul 2024 09:19:53 +0800 From: Zhenlei Huang <zlei@FreeBSD.org> To: Mark Johnston <markj@freebsd.org> Cc: freebsd-net@freebsd.org Subject: Re: flushing default router list upon inet6 route flush Message-ID: <AB0A823A-A2D0-451B-9953-77DE1268E1E4@FreeBSD.org> In-Reply-To: <ZpbSS6dltUcqNPeD@nuc> References: <ZpbSS6dltUcqNPeD@nuc>
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> On Jul 17, 2024, at 4:04 AM, Mark Johnston <markj@freebsd.org> wrote: > > Hello, > > When IPv6 SLAAC is configured for an interface, the kernel will update > its default router list upon receipt of a router advertisement. In so > doing it may install a default route; in the kernel this happens in > defrouter_addreq(). > > If one uses "route flush" or "service routing restart" to reset the > routing tables, the default router list is not purged, so a subsequent > RA from the original default router does not update the list, and so > does not re-create the default route, even if one re-runs rtsol(8). > > This appears to be a bug, but I'm not sure where best to fix it. Should > "service routing restart" invoke "ndp -R" to flush the default router > list? That can be a workaround, but not the ideal fix. > Should route(8) handle this as part of a flush command? No, I do not think so. route(8) should handle the routing / FIB parts. IPv6 default route list is maintained as a per AF basis. Handling the default route list via route(8), aka the userland, seems to be more a HACK. > Or > something else? I'd propose that the kernel handle this situation, so that for other cases such as `route -6 delete default`, or route change event from NETLINK socket, the IPv6 SLAAC default router feature can also work as expected. To be precise, `sys/netinet6/nd6_rtr.c` listen on route events and clear the `installed` flag on deleting the previously installed default route, or maybe purge all default route list. Then the next time the kernel receives a RA it re-installs the default route. This IMO may have side effect that user may really want to delete the default route while not providing an explicit default route. I think for that case user should disable accepting RA on the interface ( aka ifconfig em0 inet6 no_radr, or turn on net.inet6.ip6.no_radr globally). How about this proposal ? Best regards, Zhenlei
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