Re: [PATCH v3 net-next 1/1] Allow user to set metric on default route learned via Router Advertisement.

From: David Ahern
Date: Sat Jan 23 2021 - 00:18:35 EST

On 1/22/21 9:02 PM, Maciej Żenczykowski wrote:
> Why can't we get rid of the special case for 0 and simply make 1024 the
> default value?

That would work too.

> As for making it an RA option: it's not clear how that would work, the
> use case I see for this is for example two connections to the internet,
> of which one is clearly better (higher throughput, lower latency, lower
> packet loss, etc) then the other.
> The upstream routers would have to somehow coordinate with each other
> the metric values... that seems impossible to achieve in practice -
> unless they do something like report expected down/up
> bandwidth, latency, etc...  While some sort of policy on the machine
> itself seems much more feasible (for example wired interface > wireless
> interface > cell interface or something like that)

I was thinking the admin of the network controls the RAs and knows which
paths are preferred over the admin of the node receiving the RA (not
practical for a mobile setup with cell vs wifi, but is for a DC which is
the driving use case).

But it takes an extension to IPv6/ndisc to add metric as an RA option,
so not realistic in a reasonable time frame.