netdev - Re: [PATCH v2 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement.

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Date:   Tue, 19 Jan 2021 21:22:40 -0700
From:   David Ahern <dsahern@...il.com>
To:     praveen chaudhary <praveen5582@...il.com>
Cc:     davem@...emloft.net, kuba@...nel.org, corbet@....net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Zhenggen Xu <zxu@...kedin.com>
Subject: Re: [PATCH v2 net-next 1/1] Allow user to set metric on default route
 learned via Router Advertisement.

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. :-)