Missing IPv6 default route on protocol kernel and table master6

[Bernd Naumann]

On 2022-10-07  18:32, Ondrej Zajicek wrote:
> Does the pppoe-wan have link-local address range? Does BIRD know about it?
> What is  What is the output from BIRD command 'show interfaces'?
> 

I assume no. Like I have written, the LLA is `/128`. I do not see the 
gateway in the `neighbor` table, but local LLA and gateway LLA are 
present as host routes.

I have reverted my changes:
- No `ip -6 route add default dev pppoe-wan`
- No `route ::/0 via "pppoe-wan"` on `protocol static`


I have now:
```
root at cpe:~# ip addr show dev pppoe-wan
42: pppoe-wan: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc 
fq_codel state UNKNOWN group default qlen 3
     link/ppp
     inet 93.206.14.134 peer 62.155.247.65/32 scope global pppoe-wan
        valid_lft forever preferred_lft forever
     inet6 2003:e4:bfff:20c2:71b4:e83:65bb:a41f/64 scope global dynamic 
noprefixroute
        valid_lft 13916sec preferred_lft 1316sec
     inet6 fe80::71b4:e83:65bb:a41f/128 scope link
        valid_lft forever preferred_lft forever


root at cpe:~# ip -6 r | grep pppoe
default from 2003:e4:bf20:6d00::/56 via fe80::f6cc:55ff:fe42:1a94 dev 
pppoe-wan proto static metric 512 pref medium
default from 2003:e4:bfff:20c2::/64 via fe80::f6cc:55ff:fe42:1a94 dev 
pppoe-wan proto static metric 512 pref medium
default from fde6:a09a:b373:f0::/64 dev pppoe-wan metric 1024 pref medium
default from fde6:a09a:b373:ff::/64 dev pppoe-wan metric 1024 pref medium
2003:e4:bfff:20c2::/64 dev pppoe-wan proto bird metric 32 pref medium
fe80::71b4:e83:65bb:a41f dev pppoe-wan proto kernel metric 256 pref medium
fe80::f6cc:55ff:fe42:1a94 dev pppoe-wan metric 1 pref medium


root at cpe:~# birdc show route for ::/0
BIRD 2.0.8 ready.
Network not found


root at cpe:~# birdc show interfaces
...
pppoe-wan up (index=42)
         PtP Multicast AdminUp LinkUp MTU=1492
         93.206.14.134/32 (Preferred, opposite 62.155.247.65, scope univ)
         2003:e4:bfff:20c2:71b4:e83:65bb:a41f/64 (Preferred, scope univ)
         fe80::71b4:e83:65bb:a41f/128 (Preferred, scope link)
...
```

If I `ip route add fe80::/64 dev pppoe-wan` it makes *no* difference.

If I delete the `/128` LLA and replace it with `/64` it is still not 
present in `master6`
```
root at cpe:~# ip -6 addr show dev pppoe-wan
42: pppoe-wan: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc 
fq_codel state UNKNOWN group default qlen 3
     inet6 2003:e4:bfff:20c2:71b4:e83:65bb:a41f/64 scope global dynamic 
noprefixroute
        valid_lft 13837sec preferred_lft 1237sec
     inet6 fe80::71b4:e83:65bb:a41f/64 scope link
        valid_lft forever preferred_lft forever

pppoe-wan up (index=42)
         PtP Multicast AdminUp LinkUp MTU=1492
         93.206.14.134/32 (Preferred, opposite 62.155.247.65, scope univ)
         2003:e4:bfff:20c2:71b4:e83:65bb:a41f/64 (Preferred, scope univ)
         fe80::71b4:e83:65bb:a41f/64 (Preferred, scope link)

root at cpe:~# birdc show route for ::/0
BIRD 2.0.8 ready.
Network not found
```

But even if that would work, I would dislike it as a solution.
My question still stands: Why is the route not present in `master6`, 
*even* that I have `learn yes` for `protocol kernel`. What does make 
this ipv6 default route so special?

I'm not sure how to proceed from here on.