戸川です．
7.0-RC1 から 7.0-RELEASEにしたら，pppで以下の現象が起きるようになりました．
回避方法と合わせて投稿します．
現象: /etc/ppp/ppp.conf で 'speed 921600' とすると，ppp接続が
できないようになった．
環境: PC: 東芝 Dynabook SS S8
通信カード: ネットインデックス AX530IN (AIR EDGE PRO)
現象が起きた時の /var/log/ppp.log
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Mar 15 15:50:04 nayuki ppp[929]: Phase: Using interface: tun0
Mar 15 15:50:04 nayuki ppp[929]: Phase: deflink: Created in closed state
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: default: accept lqr
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: default: set lqrperiod 60
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: ident user-ppp VERSION
(built COMPILATIONDATE)
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set device /dev/cuau0
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set speed 921600
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set dial ABORT BUSY ABORT
NO\sCARRIER TIMEOUT 5 "" AT OK-AT-OK ATE1Q0 OK \dATDT\T TIMEOUT 40
CONNECT
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set timeout 180
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: enable dns
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: resolv writable
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set phone 0570570776##64
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set authname
[メールアドレス保護]
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: set authkey ********
Mar 15 15:50:04 nayuki ppp[929]: tun0: Command: iij: add default HISADDR
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: PPP Started (ddial mode).
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: bundle: Establish
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: closed -> opening
Mar 15 15:50:04 nayuki ppp[930]: tun0: Warning: deflink: tcsetattr: Failed
configuring device
Mar 15 15:50:04 nayuki ppp[930]: tun0: Warning: Perhaps the speed
is unsupported
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: Connected!
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: opening -> dial
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Phone: 0570570776##64
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Send: AT^M
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Expect(5): OK
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Received:
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Received:
Mar 15 15:50:04 nayuki ppp[930]: tun0: Chat: Received: NO CARRIER
Mar 15 15:50:04 nayuki ppp[930]: tun0: Warning: Chat script failed
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: dial -> hangup
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: Disconnected!
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: Connect time: 0 secs: 0
octets in, 0 octets out
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: 0 packets in, 0 packets
out
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: total 0 bytes/sec, peak 0
bytes/sec on Sat Mar 15 15:50:04 2008
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: hangup -> opening
Mar 15 15:50:04 nayuki ppp[930]: tun0: Phase: deflink: Enter pause (30) for
redialing.
----
回避方法: 'speed 460800' とする．
# speedの取れる値は， /usr/src/usr.sbin/ppp/defs.c を見て決めました．
以上です．
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