[openib-general] IPv6 All Router Multicast Group

[Roland Dreier]

    Hal> Routers send router advertisements periodically.

yes.

    Hal> If a hosts does not receive any router advertisements in some
    Hal> time period, it will solicit for routers (send a router
    Hal> solicitation message) some number of times.

yes, it will send router solicitation messages to the all-routers group.

    Hal> So maybe IPv6 unicast routers don't need to receive on this
    Hal> group (hosts definitely do).

I think unicast routers would need to listen to the all-routers
group.  However, since router advertisements are sent to the all-nodes
group, a typical IPv6 end node does not need to listen to the
all-routers group (which is why the kernel doesn't join the
all-routers group by default).

    Hal> For IGMP, I think both hosts and routers need to both send
    Hal> and receive yet we see a send only join for this group.

OK, not sure how IGMP works on the host side.

    Hal> The same thing appears to be occuring in these IPv4 (all
    Hal> routers and IGMP).

The only IPv4 group I see my systems joining is the broadcast group --
maybe you have more config options turned on than I do; I'm running

# CONFIG_IP_ADVANCED_ROUTER is not set
# CONFIG_IP_MROUTE is not set

 - Roland