linux-kernel - Re: This counter "ip6InNoRoutes" does not follow the RFC4293 specification implementation

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Date:   Wed, 16 Feb 2022 19:59:50 -0700
From:   David Ahern <dsahern@...nel.org>
To:     "Xiao, Jiguang" <Jiguang.Xiao@...driver.com>,
        "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>
Subject: Re: This counter "ip6InNoRoutes" does not follow the RFC4293
 specification implementation

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