Date: Tue, 10 Jul 2007 18:13:48 -0600 From: Brett Glass <brett@lariat.net> To: net@freebsd.org Subject: Bug in userland PPP LQR? Message-ID: <200707110014.SAA02181@lariat.net>
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I may have found a bug in the LQR code of FreeBSD's userland PPP. I've been noticing that PPTP sessions are dropping with messages saying "** Too many LQR packets lost **" on some important wireless links. Wireless links occasionally do drop a packet or two, but it's rare to see 5 dropped packets in a row (which is supposed to be when PPP gives up and kills the link). Yet, the links go down when there's even an occasional dropped packet. I'm using LQR with an interval of 12 seconds, and the built-in threshold for dropping the connection (not changeable in this implementation) is 5 lost packets. This means that the link pretty much has to be down for 60 seconds before the connection gets cut off. In practice, however, connections are dying when data was coming through only a few seconds before and there's a very low percentage of dropped packets. This leads me to suspect that either (a) the lost packet counter is cumulative for the session; that is, it's not resetting when a good response comes in; or (b) the LQR mechanism it may be getting out of sync (perhaps due to unexpected sequence numbers) and always count up to 5 after the first missed packet. The code in /usr/src/usr.sbin/ppp/lqr.c is quite cryptic, and I'd like some help in figuring out just why I'm seeing so many dropped connections due to LQR. Any folks out there willing to help me analyze it? --Brett Glass
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