netdev - RE: This counter "ip6InNoRoutes" does not follow the RFC4293 specification implementation

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Date:   Wed, 9 Mar 2022 02:16:12 +0000
From:   "Xiao, Jiguang" <Jiguang.Xiao@...driver.com>
To:     David Ahern <dsahern@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Pudak, Filip" <Filip.Pudak@...driver.com>
Subject: RE: This counter "ip6InNoRoutes" does not follow the RFC4293
 specification implementation

Hi David

To confirm whether my test method is correct, could you please briefly describe your test procedure? 



Best Regards
Xiao Jiguang

-----Original Message-----
From: Xiao, Jiguang 
Sent: 2022年2月24日 17:04
To: David Ahern <dsahern@...nel.org>; davem@...emloft.net; yoshfuji@...ux-ipv6.org; kuba@...nel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org
Cc: Pudak, Filip <Filip.Pudak@...driver.com>
Subject: RE: This counter "ip6InNoRoutes" does not follow the RFC4293 specification implementation

Hi David

Thanks for guiding me how to proceed. I have captured the output result of perf (perf_output_5.10.49). 

To confirm the problem, I tested it again on Ubuntu (kernel version is 5.4.0-79) using Docker and the results were the same, the only difference is the kernel version. I also collected the perf results and added them to the attachment (perf_output_5.4.0).



Best Regards
Xiao Jiguang

-----Original Message-----
From: David Ahern <dsahern@...nel.org>
Sent: 2022年2月17日 11:00
To: Xiao, Jiguang <Jiguang.Xiao@...driver.com>; davem@...emloft.net; yoshfuji@...ux-ipv6.org; kuba@...nel.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org
Subject: Re: This counter "ip6InNoRoutes" does not follow the RFC4293 specification implementation

[Please note: This e-mail is from an EXTERNAL e-mail address]

On 2/16/22 3:36 AM, Xiao, Jiguang wrote:
> Hello,
>
> I found a counter in the kernel(5.10.49) that did not follow the
> RFC4293 specification. The test steps are as follows:
>
>
>
> Topology:
>
>   |VM 1| ------ |linux| ------ |VM 2|
>
>
>
> Steps:
>
> 1. Verify that “VM1” is reachable from “VM 2” and vice versa using
> ping6 command.
>
> 2. On “linux” node, in proper fib, remove default route to NW address 
> which “VM 2” resides in. This way, the packet won’t be forwarded by 
> “linux” due to no route pointing to destination address of “VM 2”.
>
> 3. Collect the corresponding SNMP counters from “linux” node.
>
> 4. Verify that there is no connectivity from “VM 1” to “VM 2” using
> ping6 command.
>
> 5. Check the counters again.
>
>
>
> The test results:
>
> The counter “ip6InNoRoutes” in “/proc/net/dev_snmp6/” has not 
> increased accordingly. In my test environment, it was always zero.
>
>
>
> My question is :
>
> Within RFC4293, “ipSystemStatsInNoRoutes” is defined as follows:
>
>   “The number of input IP datagrams discarded because no route could 
> be found to transmit them to their destination.”
>
> Does this version of the kernel comply with the RFC4293 specification?
>
>

I see that counter incrementing. Look at the fib6 tracepoints and see what the lookups are returning:

perf record -e fib6:* -a
<run test>
Ctrl-C
perf script