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Date: Wed, 30 Jul 2014 18:52:21 +0200 From: Hannes Frederic Sowa <hannes@...essinduktion.org> To: David Lamparter <equinox@...c24.net> Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org, Stephen Hemminger <stephen@...workplumber.org> Subject: Re: [PATCH net-next] ipv6: addrconf: fix mcast route for GRE devices On Mi, 2014-07-30 at 18:31 +0200, David Lamparter wrote: > On Wed, Jul 30, 2014 at 06:09:27PM +0200, Hannes Frederic Sowa wrote: > [cut] > > > On Wed, Jul 30, 2014 at 05:14:42PM +0200, Hannes Frederic Sowa wrote: > > > > On Mi, 2014-07-30 at 02:55 +0200, David Lamparter wrote: > > > > > GRE devices, for some reason, were coming up with an autoconfigured > > > > > address, but no ff00::/8 route in the local table. This breaks any kind > > > > > of multicast, in particular OSPFv3, mDNS, - and ND. In fact, IPv6 only > > > > > works at all because there is little need for ND on PtP devices. > > > > > > > > > > Adding any other IPv6 address on the device would rectify this issue > > > > > through inet6_addr_add()/addrconf_add_dev() - and would leave the route > > > > > around even if the address was later removed. (This is probably why > > > > > this issue was not discovered earlier. AFAICS it has been there from > > > > > the beginning, e.g. aee80b5 "generate link local address for GRE > > > > > tunnel") > > > > > > > > Yep, this is poor, but changing this will break user space... > > > > > > How exactly will this break user space? > > > > Because the multicast routes will always be restored after e.g. a route > > flush or manual route deletion. Scripts might depend on this. > > Sorry, I still don't get it. Without this patch you end up in an > inconsistent state, where a LL addr exists, but multicast doesn't work > (since ff00::/8 is missing from RT6_TABLE_LOCAL). Sure, people can remove addresses and routes at will. > Userspace is not supposed to touch RT6_TABLE_LOCAL in general, and, the > kernel will actually refuse installing the ff00::/8 route into the local > table from userspace (because there will be other ff00::/8 routes from > other interfaces, so you get "File exists"). You can delete the route > (and thus break mcast), but not add it. The only way to add it is to > add an address. People really do flush the routing table. I'll have a look why the addition of the multicast route throws an error. > Not changing this behaviour keeps breaking userspace; ospf6d among > other things assumes an interface has working IPv6 when a link-local > address is present. Yeah, but in the end, people also can drop specific packets and we cannot do anything. Bye, Hannes -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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