netdev - Re: selftest fib_nexthop_multiprefix failed due to route mismatch

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Date: Wed, 6 Dec 2023 11:47:57 +0800
From: Hangbin Liu <liuhangbin@...il.com>
To: David Ahern <dsahern@...nel.org>
Cc: netdev@...r.kernel.org
Subject: Re: selftest fib_nexthop_multiprefix failed due to route mismatch

On Tue, Nov 21, 2023 at 09:40:02AM -0800, David Ahern wrote:
> On 11/20/23 10:40 PM, Hangbin Liu wrote:
> > Hi David,
> > 
> > Recently when run fib_nexthop_multiprefix test I saw all IPv6 test failed.
> > e.g.
> > 
> > # ./fib_nexthop_multiprefix.sh
> > TEST: IPv4: host 0 to host 1, mtu 1300                              [ OK ]
> > TEST: IPv6: host 0 to host 1, mtu 1300                              [FAIL]
> > 
> > With -v it shows
> > 
> > COMMAND: ip netns exec h0 /usr/sbin/ping6 -s 1350 -c5 -w5 2001:db8:101::1
> > PING 2001:db8:101::1(2001:db8:101::1) 1350 data bytes
> > From 2001:db8:100::64 icmp_seq=1 Packet too big: mtu=1300
> > 
> > --- 2001:db8:101::1 ping statistics ---
> > 1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
> > 
> > Route get
> > 2001:db8:101::1 via 2001:db8:100::64 dev eth0 src 2001:db8:100::1 metric 1024 expires 599sec mtu 1300 pref medium
> > Searching for:
> >     2001:db8:101::1 from :: via 2001:db8:100::64 dev eth0 src 2001:db8:100::1 .* mtu 1300
> > 
> > TEST: IPv6: host 0 to host 1, mtu 1300                              [FAIL]
> > 
> > So we can get the Packet too big from 2001:db8:100::64 successfully. There
> > is no "from ::" anymore. I plan to fix this issue. But I can't find which
> > commit changed the behavior and the client could receive Packet too big
> > message with correct src address.
> > 
> > Do you have any hints?
> > 
> > Thanks
> > Hangbin
> 
> v6.3.12:
> 
> $ sudo /mnt/hostshare/fib_nexthop_multiprefix.sh
> TEST: IPv4: host 0 to host 1, mtu 1300                          [ OK ]
> TEST: IPv6: host 0 to host 1, mtu 1300                          [ OK ]
> 
> v6.4.13 all passed as well, so it is something recent. I do not have a
> 6.5 or 6.6 kernels compiled at the moment.

Hi David,

I re-test this on 6.4.0 and it also failed. So this looks like an env issue
on your side?

# uname -r
6.4.0
# ./fib_nexthop_multiprefix.sh
TEST: IPv4: host 0 to host 1, mtu 1300                              [ OK ]
TEST: IPv6: host 0 to host 1, mtu 1300                              [FAIL]

And from the test result, it looks we should receive the Packet too big message
from r1. So look the current checking is incorrect and the "from ::" checking
should be removed.

Please fix me if I missed anything?

Thanks
Hangbin