Christopher Zimmermann(chr...@openbsd.org) on 2020.01.15 11:55:43 +0100:
> Hi,
>
> as far as I can see a dual stack carp interface does not care whether it
> receives advertisements addressed to IPv4 or IPv6. Any one will do.
> So I propose to send IPv6 advertisements only when IPv4 is not possible.
>
> Why?
>
> - Noise can be reduced by using unicast advertisements.
> This is only possible for IPv4 by ``ifconfig carppeer``.
> I don't like flooding the whole network with carp advertisements when
> I may also unicast them.
Maybe i'm getting confused, but in the problem description you were talking
about v6 vs v4, and here you argue about unicast (vs multicast?) being
better. Thats orthogonal, isnt it?
> - breaking IPv6 connectivity (for example by running iked without -6)
> will start a preempt-war, because failing ip6_output will cause the
> demote counter to be increased. That's what hit me.
But the whole point of carp is to notice broken connectivity. If you run v6
on an interface, you want to know if its working, no?
At the very least, this needs some more thought and testing in all the ways
carp can be configured.
> I would suggest a change like this:
>
> Index: ip_carp.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet/ip_carp.c,v
> retrieving revision 1.342
> diff -u -p -r1.342 ip_carp.c
> --- ip_carp.c 8 Nov 2019 07:51:41 -0000 1.342
> +++ ip_carp.c 15 Jan 2020 10:45:56 -0000
> @@ -1175,7 +1175,7 @@ carp_send_ad(struct carp_vhost_entry *vh
> }
> }
> #ifdef INET6
> - if (sc->sc_naddrs6) {
> + else if (sc->sc_naddrs6) {
> struct ip6_hdr *ip6;
>
> MGETHDR(m, M_DONTWAIT, MT_HEADER);
>
>
> one could also use a slightly smaller hammer and only avoid sending IPv6
> if the user requested an IPv4 unicast address:
>
> - if (sc->sc_naddrs6) {
> + if (sc->sc_naddrs6 &&
> + (! sc->sc_naddrs ||
> + sc->sc_peer.s_addr == INADDR_CARP_GROUP) ) {
>
>
> Christopher
>
>
> --
> http://gmerlin.de
> OpenPGP: http://gmerlin.de/christopher.pub
> CB07 DA40 B0B6 571D 35E2 0DEF 87E2 92A7 13E5 DEE1
>
