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Subject: Re: [PATCH v2 net-next 1/1] Allow user to set metric on default route
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From:   praveen chaudhary <praveen5582@gmail.com>
In-Reply-To: <7839be40-6555-3e5a-3459-c3f0e4726795@gmail.com>
Date:   Tue, 19 Jan 2021 22:51:27 -0800
Cc:     davem@davemloft.net, kuba@kernel.org, corbet@lwn.net,
        kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org,
        netdev@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Zhenggen Xu <zxu@linkedin.com>
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References: <20210115080203.8889-1-pchaudhary@linkedin.com>
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 <A2DE27CF-A988-4003-8A95-60CC101086DA@gmail.com>
 <7839be40-6555-3e5a-3459-c3f0e4726795@gmail.com>
To:     David Ahern <dsahern@gmail.com>
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> On Jan 19, 2021, at 8:22 PM, David Ahern <dsahern@gmail.com> wrote:
>=20
> On 1/19/21 3:17 PM, praveen chaudhary wrote:
>>>> ----------------------------------------------------------------
>>>> For IPv4:
>>>> ----------------------------------------------------------------
>>>>=20
>>>> Config in etc/network/interfaces
>>>> ----------------------------------------------------------------
>>>> ```
>>>> auto eth0
>>>> iface eth0 inet dhcp
>>>>   metric 4261413864
>>>=20
>>> how does that work for IPv4? Is the metric passed to the dhclient =
and it
>>> inserts the route with the given metric or is a dhclient script used =
to
>>> replace the route after insert?
>>>=20
>>>=20
>>=20
>> Yes, DHCP client picks config under =E2=80=9Ciface eth0 inet dhcp=E2=80=
=9D line and if metric is configured, then it adds the metric for all =
added routes.
>=20
> As I recall ifupdown{2} forks dhclient as a process to handle dhcp
> config, and I believe there is a script that handles adding the =
default
> route with metric. Meaning ... it is not comparable to an RA.
>=20

I hope, we both will agree that a fixed metric value on default route =
learned via RA=20
restricts Network Administrators today. And such issues hinder the =
deployment
of IPv6 only networks. So if we agree that in future we may need to =
allow  a
configurable value for metric then this fix makes good sense.
BTW, kindly let me know if there is a better way to configure this =
metric. I think,
sysctl is the only way.


>>=20
>> Thanks a lot again for spending time for this Review,
>> This feature will help SONiC OS [and others Linux flavors] for better =
IPv6 support, so thanks again.
>=20
> I think SONiC is an abomination, so that is definitely not the
> motivation for my reviews. :-)
>=20

Trying to make things better day by day. That is the only solace for =
Software Engineers :-).=20

I really appreciate for your time to review this patch. Cheers.