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Date:   Mon, 21 Sep 2020 14:44:39 -0400 (EDT)
From:   Mathieu Desnoyers <>
To:     David Ahern <>
Cc:     "David S. Miller" <>,
        netdev <>,
        linux-kernel <>
Subject: Re: [RFC PATCH v2 0/3] l3mdev icmp error route lookup fixes

----- On Sep 21, 2020, at 2:36 PM, David Ahern wrote:

> On 9/18/20 12:17 PM, Mathieu Desnoyers wrote:
>> Hi,
>> Here is an updated series of fixes for ipv4 and ipv6 which which ensure
>> the route lookup is performed on the right routing table in VRF
>> configurations when sending TTL expired icmp errors (useful for
>> traceroute).
>> It includes tests for both ipv4 and ipv6.
>> These fixes address specifically address the code paths involved in
>> sending TTL expired icmp errors. As detailed in the individual commit
>> messages, those fixes do not address similar issues related to network
>> namespaces and unreachable / fragmentation needed messages, which appear
>> to use different code paths.
> New selftests are failing:
> TEST: Ping received ICMP frag needed                       [FAIL]
> Both IPv4 and IPv6 versions are failing.

Indeed, this situation is discussed in each patch commit message:


[ It has also been pointed out that a similar issue exists with
  unreachable / fragmentation needed messages, which can be triggered by
  changing the MTU of eth1 in r1 to 1400 and running:

  ip netns exec h1 ping -s 1450 -Mdo -c1

  Some investigation points to raw_icmp_error() and raw_err() as being
  involved in this last scenario. The focus of this patch is TTL expired
  ICMP messages, which go through icmp_route_lookup.
  Investigation of failure modes related to raw_icmp_error() is beyond
  this investigation's scope. ]


[ Testing shows that similar issues exist with ipv6 unreachable /
  fragmentation needed messages.  However, investigation of this
  additional failure mode is beyond this investigation's scope. ]

I do not have the time to investigate further unfortunately, so I
thought it best to post what I have.

Note that network namespaces also probably have the same problem,
but those are not covered by the test cases.



Mathieu Desnoyers
EfficiOS Inc.

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