Linux and ULA support and default route

Holger Zuleger Holger.Zuleger at
Fri Oct 14 13:51:41 CEST 2016

On 14.10.2016 12:32, Gert Doering wrote:
> Hi,
> On Fri, Oct 14, 2016 at 12:00:04PM +0200, Holger Zuleger wrote:
>> Of course the default route should *not* be withdrawn.
>> The RA default router announcement says just, "Hey hosts, I'm the way
>> out of your local subnet", and not "Hey host, I have a upstream
>> connection to the rest of the internet".
> If the router has no default route, it should not announce one - this
> is why PIO exists for more specific info.
For cases where a router provides "in principle" only connectivity to a
limited set of prefixes (think of VPN connection) I'm with you.

> Imagine a setup with *two* routers.  One of them has broken Internet,
> the other is working.  How can the hosts decide if both keep announcing
> themselves as "I can reach anything"?
This is just a corner case if both routers have directly the upstream
connection. But then this behavior make only sense if the same prefix is
used for both upstreams, which is seldom the case in residential user
Otherwise you have a lot to do with source specific routing, and yes,
you are right: In this case the source specific default route for the
failed prefix should no longer announced.

Holger Zuleger

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