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Bug#901255: netcfg-static: Unable to configure fe80::1 as a gateway

On 6/10/18 7:25 PM, Samuel Thibault wrote:
> Igor Scheller, le dim. 10 juin 2018 18:57:50 +0200, a ecrit:
>> When I try to configure fe80::1 (next router) as a gateway in an IPv6 only
>> network the installer stops with an "Unreachable gateway" error.
>> Looking at netcfg-common.c:netcfg_gateway_reachable its checked by comparing
>> bytes. Imho a better way would be to configure the interface and ping the
>> gateway?
> Well, the gateway has no obligation to respond to pings, so it's not a
> proper way.
> Checking that the prefix matches however makes complete sense, and
> should just work.  Provided that the network prefix length is correct,
> of course, but it has to be otherwise it's a configuration error. I
> guess the problem is rather there.

Well, the gateway may as well be link-local and not be in the assigned
prefix. That's unfortunately a valid configuration. I wouldn't call
fe80::1 "next router", though. It's not a well-known address. ff02::2
(all routers) would be, in a way. But alas.

I guess the answer here is that if the gateway is in fe80::/10 the route
needs to be added with the interface's name, just like pointopoint does it.

The better setup is to use autoconfiguration and let the router announce
itself. That's how most production IPv6 setups work because the standard
calls for that. But I know that especially providers like Hetzner are
notorious for requiring their users to use a hard-coded fe80::1 default
gateway. (And ifupdown supports this correctly.)

Kind regards
Philipp Kern

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