Advertise IPs as single regardless of prefix

[Alexander Zubkov]

I've also made a quick patch for the kerenel protocol to accept routes of
type local. But it might be not well backward-compatible, because somebody
might receive some new routes in their kernel protocols. Anyway, with this
patch you can use something like that to have your IP route:

protocol kernel6 {
    kernel table 255; # table local
    learn all; # accept kernel routes as well
    scan time 10;
    ipv6 {
        import all;
        export none;
    };
}

On Tue, Sep 30, 2025 at 8:39 PM Alexander Zubkov <green at qrator.net> wrote:

> Hi Anthony,
>
> You mean you have for example ip address with mask configured on eth0:
> 2001:db8::cafe/64. And you want to have route 2001:db8::cafe/128 inside
> bird without having to specify it manually in a static protocol for
> example? And now you have to make a dummy interface with 2001:db8::cafe/128
> configured on it?
> AFAIK, you cannot do that automatically in bird (i.e. change network mask
> of prefix). I thought if it would be possible to import single IP route
> from "table local", Linux has such routes for IPs configured for the system:
>
> local 2001:db8::cafe dev eth0 table local proto kernel metric 0 pref medium
>
> But bird ignores routes with type local, so it would need some patching of
> the source to do that.
> Also IMHO, having IPs with overlapping prefixes should work well on Linux
> if you know what you do.
> You can also use such config, when you configure for
> example 2001:db8::cafe/128 on eth0 and add device-route for 2001:db8::/64
> on dev eth0. But that might not work for automatic configurations - DHCP,
> SLAAC.
>
> Regards,
> Alexander Zubkov
>
>
> On Tue, Sep 30, 2025 at 7:24 PM Anthony Hoppe via Bird-users <
> bird-users at network.cz> wrote:
>
>> Hello List!
>>
>> I am working on a project to bring L3 down to the individual host and
>> am thinking through the transitionary configuration.
>>
>> For the purposes of this discussion, the hosts are assigned IPv4
>> addresses within a /24 and IPv6 addresses within a /64.
>>
>> Currently, I'm using a dummy interface and adding the IPs they own as
>> v4 /32 and v6 /128 and in combination with an export filter to only
>> export /32 and /128 prefixes, this works great.
>>
>> However, I was wondering if there is a way to configure BIRD so that
>> for the IPs configured on the host it supplants the configured prefix
>> with /32 and/or /128 allowing me to eliminate the dummy interface?
>>
>> The dummy interface is mostly a transitory step as Linux (Debian, at
>> least) will not let me assign a /32 or /128 to an interface where a
>> larger overlapping prefix resides (which yes, I understand why you
>> normally don't want to do this, haha).
>>
>> ~ Anthony
>>
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