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([2601:282:800:fd80:d059:3694:77c1:5391]) by smtp.googlemail.com with ESMTPSA id x13sm1458840ioj.18.2019.07.10.05.27.32 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Jul 2019 05:27:32 -0700 (PDT) Subject: Re: Question about linux kernel commit: "net/ipv6: move metrics from dst to rt6_info" To: Jan Szewczyk , "davem@davemloft.net" References: Cc: "netdev@vger.kernel.org" From: David Ahern Message-ID: Date: Wed, 10 Jul 2019 06:27:31 -0600 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org [ adding netdev so others can chime in ] On 7/10/19 2:28 AM, Jan Szewczyk wrote: > Hi guys! > > We can see different behavior of one of our commands that supposed to > show pmtu information. > > It’s using netlink message RTM_GETROUTE to get the information and in > Linux kernel version 4.12 after sending big packet (and triggering > “packet too big”) there is an entry with PMTU and expiration time. > > In the version 4.18 unfortunately the entry looks different and there is > no PMTU information. Can you try with 4.19.58 (latest stable release for 4.19)? Perhaps there was a bugfix that is missing from 4.18. The kernel has 2 commands under tools/testing/selftests/net -- pmtu.sh and icmp_redirect.sh -- that verify exceptions are created and use 'ip ro get' to verify the mtu. > > I can see that in your commit > https://github.com/torvalds/linux/commit/d4ead6b34b67fd711639324b6465a050bcb197d4, > these lines disappeared from route.c: > >   > >      if (rt->rt6i_pmtu) > >            metrics[RTAX_MTU - 1] = rt->rt6i_pmtu; > >   > > I’m very beginner in linux kernel code, can you help me and tell me if > that could cause this different behavior? > >   > >   > > BR, > > Jan Szewczyk >