On 4.99.28/sparc64, my pppoe(4) connection works just fine (apart from
the fact that IPv6 negotiation fails while it works with rp-pppoe, but I
guess that's another story---which I haven't looked into yet):

| $ ifconfig pppoe0
| pppoe0: flags=8851<UP,POINTOPOINT,RUNNING,SIMPLEX,MULTICAST> mtu 1424
|         inet 217.197.85.252 -> 192.109.42.188 netmask 0xff000000
|         inet6 fe80::a00:20ff:feac:1643%pppoe0 ->  prefixlen 64 scopeid 0x4

However:

| $ pppoectl -d pppoe0
| pppoe0: interface not found

To get the session state, pppoectl(8) does an ioctl(2) call with a
PPPOEGETSESSION request, which should be handled by pppoe(4)'s
pppoe_ioctl().  PPPOEGETSESSION evaluates to 3223349616.  However, I
added some debug output to sys/net/if_pppoe.c and for some reason,
pppoe_ioctl() receives 3230689648 via its "cmd" argument.  Therefore,
the call isn't caught by the PPPOEGETSESSION case within pppoe_ioctl().
Instead, it's handled by the default case, which hands it over to
sys/net/if_spppsubr.c:sppp_ioctl(), which in turn returns ENOTTY.

I didn't use pppoe(4) before, so I don't know whether this problem is
new.  Can others reproduce it?  Any ideas?

Holger