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Date: Wed, 30 Jul 2014 13:20:00 -0500 From: Dan Williams <dcbw@...hat.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> Cc: David Lamparter <equinox@...c24.net>, netdev@...r.kernel.org, Stephen Hemminger <stephen@...workplumber.org> Subject: Re: [PATCH net-next] ipv6: addrconf: fix mcast route for GRE devices On Wed, 2014-07-30 at 20:03 +0200, Hannes Frederic Sowa wrote: > On Wed, Jul 30, 2014, at 19:35, David Lamparter wrote: > > On Wed, Jul 30, 2014 at 06:52:21PM +0200, Hannes Frederic Sowa wrote: > > > 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. > > > > That's not the point. > > > > user manually adds address on any if: ff00::/8 added. > > kernel link-up autoconf addr on !gre: ff00::/8 added. > > kernel link-up autoconf addr on gre: no ff00::/8. > > Ah sorry, I am ok with your patch that we generate a ff00::/8 multicast > route if we set a gre interface up. Getting rid of the logic, that we > try to add the ff00::/8 on every addition of an address to an interface > would be a change which concerns because of backward compatibility > reasons. With IPv6LL address generation modes (IFLA_INET6_ADDR_GEN_MODE) the kernel might not be handling the LL address, so I'd like to keep addrconf_add_dev() in the inet6_addr_add() codepath. Having the multicast route is useful/correct no matter who adds the LL address to the interface. I think you alluded to this earlier, but I just wanted to bring it up. Dan > Especially this also creates multicast routes on sit-non-ptp/isatap > routes, which actually don't need one. > > > This is about automatic kernel behaviour in device up/change > > notifications. The user can always shoot himself in the foot. This is > > the kernel shooting the user in the foot in one particular and quite > > specific instance and without a request to do so. > > Agreed. > > > > > 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. > > > > This is RT6_TABLE_LOCAL. Most people aren't even aware it exists. And > > even though I can't find a reference for it, my memory tells me that > > "table local" is supposed to be under the kernel's authority. > > Yep, but still provide ip -6 route flush table all, which also clears > the local table. And I guess people depend on ff00:: multicast routes > being inserted as soon as they add addresses. > > 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 -- 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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