netdev - Re: selftest fib_nexthop_multiprefix failed due to route mismatch

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Date: Fri, 8 Dec 2023 12:21:55 -0700
From: David Ahern <dsahern@...nel.org>
To: Hangbin Liu <liuhangbin@...il.com>
Cc: netdev@...r.kernel.org
Subject: Re: selftest fib_nexthop_multiprefix failed due to route mismatch

On 12/5/23 8:47 PM, Hangbin Liu wrote:
> 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?
> 

I ran it in a ubuntu 20.04 VM. Do not recall any specific sysctl
settings to the VM, but maybe something is different between U20.04 and
your OS