Re: RTM_DELROUTE not sent anymore when deleting (last) nexthop of routes in 6.1

[Jonas Gorski <jonas.gorski@gmail.com>]

On Thu, 24 Nov 2022 at 15:15, Jonas Gorski <jonas.gorski@gmail.com> wrote:
>
> Hi Ido,
>
> On Thu, 24 Nov 2022 at 13:41, Ido Schimmel <idosch@idosch.org> wrote:
> >
> > On Thu, Nov 24, 2022 at 10:20:00AM +0100, Jonas Gorski wrote:
> > > Hello,
> > >
> > > when an IPv4 route gets removed because its nexthop was deleted, the
> > > kernel does not send a RTM_DELROUTE netlink notifications anymore in
> > > 6.1. A bisect lead me to 61b91eb33a69 ("ipv4: Handle attempt to delete
> > > multipath route when fib_info contains an nh reference"), and
> > > reverting it makes it work again.
> > >
> >
> > Are you running an upstream kernel?
>
> Okay, after having a second look, you are right, and I got myself
> confused by IPv6 generating RTM_DELROUTE notifications, but which is
> besides the point.
>
> The point where it fails is that FRR tries to delete its route(s), and
> fails to do so with this commit applied (=> RTM_DELROUTE goes
> missing), then does the RTM_DELNEXTHOP.
>
> So while there is indeed no RTM_DELROUTE generated in response to the
> kernel, it was generated when FRR was successfully deleting its routes
> before.
>
> Not sure if this already qualifies as breaking userspace though, but
> it's definitely something that used to work with 6.0 and before, and
> does not work anymore now.
>
> The error in FRR log is:
>
> [YXPF5-B2CE0] netlink_route_multipath_msg_encode: RTM_DELROUTE
> 10.0.1.0/24 vrf 0(254)
> [HYEHE-CQZ9G] nl_batch_send: netlink-dp (NS 0), batch size=44, msg cnt=1
> [XS99C-X3KS5] netlink-dp (NS 0): error: No such process
> type=RTM_DELROUTE(25), seq=22, pid=2419702167
>
> with the revert it succeeds.
>
> I'll see if I can get a better idea of the actual netlink message sent.

Okay, found the knob:

nlmsghdr [len=44 type=(25) DELROUTE flags=(0x0401)
{REQUEST,(ATOMIC|CREATE)} seq=22 pid=2185212923]
  rtmsg [family=(2) AF_INET dstlen=24 srclen=0 tos=0 table=254
protocol=(186) UNKNOWN scope=(0) UNIVERSE type=(0) UNSPEC flags=0x0000
{}]
    rta [len=8 (payload=4) type=(1) DST]
      10.0.1.0
    rta [len=8 (payload=4) type=(6) PRIORITY]
      20
netlink-dp (NS 0): error: No such process type=RTM_DELROUTE(25),
seq=22, pid=2185212923

The route was created via

nlmsghdr [len=52 type=(24) NEWROUTE flags=(0x0501)
{REQUEST,DUMP,(ROOT|REPLACE|CAPPED),(ATOMIC|CREATE)} seq=18
pid=2185212923]
 rtmsg [family=(2) AF_INET dstlen=24 srclen=0 tos=0 table=254
protocol=(186) UNKNOWN scope=(0) UNIVERSE type=(1) UNICAST
flags=0x0000 {}]
    rta [len=8 (payload=4) type=(1) DST]
      10.0.1.0
    rta [len=8 (payload=4) type=(6) PRIORITY]
       20
     rta [len=8 (payload=4) type=(30) NH_ID]
     18

and for completion the nexthop is created via:

nlmsghdr [len=48 type=(104) NEWNEXTHOP flags=(0x0501)
{REQUEST,DUMP,(ROOT|REPLACE|CAPPED),(ATOMIC|CREATE)} seq=17
pid=2185212923]
   nhm [family=(2) AF_INET scope=(0) UNIVERSE protocol=(11) ZEBRA
flags=0x00000000 {}]
    rta [len=8 (payload=4) type=(1) ID]
      18
    rta [len=8 (payload=4) type=(6) GATEWAY]
      10.0.0.1
    rta [len=8 (payload=4) type=(5) OIF]
      62


Regards
Jonas