Not quite sure why, but after running smoothly for a few days the OpenBSD DSL router suddenly started having problems reconnecting after the daily disconnect (it's attached to Deutsche Telekom's T-DSL service, which forces a reconnect after 24 hours). The log filled with messages like this:
Apr 16 10:02:36 akita ppp[18390]: tun0: IPCP: IPADDR[6] 2xx.x.1xx.x Apr 16 10:02:36 akita ppp[18390]: tun0: IPCP: deflink: Oops, RCR in Initial. Apr 16 10:02:39 akita ppp[18390]: tun0: IPCP: deflink: RecvConfigReq(12) state = Initial
Killing ppp
and manually redialling resulted in an instant
reconnection.