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Subject: Re: [PATCH v2 net-next 1/1] Allow user to set metric on default route
 learned via Router Advertisement.
To:     praveen chaudhary <praveen5582@gmail.com>
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>
References: <20210115080203.8889-1-pchaudhary@linkedin.com>
 <0f64942e-debd-81bd-b29c-7d2728a5bd4b@gmail.com>
 <A2DE27CF-A988-4003-8A95-60CC101086DA@gmail.com>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <7839be40-6555-3e5a-3459-c3f0e4726795@gmail.com>
Date:   Tue, 19 Jan 2021 21:22:40 -0700
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On 1/19/21 3:17 PM, praveen chaudhary wrote:
>>> ----------------------------------------------------------------
>>> For IPv4:
>>> ----------------------------------------------------------------
>>>
>>> Config in etc/network/interfaces
>>> ----------------------------------------------------------------
>>> ```
>>> auto eth0
>>> iface eth0 inet dhcp
>>>    metric 4261413864
>>
>> 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?
>>
>>
> 
> Yes, DHCP client picks config under “iface eth0 inet dhcp” line and if metric is configured, then it adds the metric for all added routes.

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.

> 
> 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.

I think SONiC is an abomination, so that is definitely not the
motivation for my reviews. :-)