netdev - Re: [PATCH 1/1] Network: support default route metric per interface

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Date:   Mon, 28 Sep 2020 20:06:32 -0700
From:   David Ahern <dsahern@...il.com>
To:     Qingtao Cao <qingtao.cao.au@...il.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, corbet@....net,
        Qingtao Cao <qingtao.cao@...i.com>,
        David Leonard <david.leonard@...i.com>
Subject: Re: [PATCH 1/1] Network: support default route metric per interface

On 9/28/20 6:54 PM, Qingtao Cao wrote:
> Hi David,
> 
> I understand I can use the "metric" parameter along with the "ip addr
> add/change" and "ip route add/change" commands to make use of the
> IFA_RT_PRIORITY attribute to explicitly specify the metric for routes
> created directly or associated with added addresses, and the network
> manager should do this.
> 
> But what if userspace can bypass the network manager? or forgetting to
> apply the "metric" parameter for example directly on the CLI?

use a sticky note? :-)

> 
> Then the kernel will fall back on the same default metric (such as 0 for
> ipv4 and IP6_RT_PRIO_ADDRCONF(256) or USER(1024) for ipv6) for ALL
> interfaces. So I think the def_rt_metric patchset can be regarded as
> having the kernel providing a mechanism for the uerspace to specify
> DIFFERENT default routes per interface, which does not necessarily
> indulge the userspace network manager skipping over specifying the metic
> explicitly
> 
> What do you think?
> 

I think it is a userspace, configuration management problem.