Sim connection timeout

I'm experiencing this problem for about a week now, in irregular intervals, sometimes every few minutes, sometimes after hours of being logged into SL without any problems. What happens is that the sim connections time out, but not the userserver. In the Alt-1 status window, the userserver is still pinging, while the sim is not, and eventually is tinted red on the map (no, not crashed).

A simultaneously running mtr shows no packet loss at all (though I've beeng using userserver.agni.lindenlab.com as destinaion, I'll try a sim now).

Here is the relevant part from my logfile:

2003-12-07T06:32:29 W. Europe Standard Time INFO LSL Bytecode saved
2003-12-07T06:32:29 W. Europe Standard Time INFO Requesting xfer from 63.211.151.57:12035 for file: C:\Documents and Settings\bzzt\Application Data\SecondLife\cache\inventory_2eadd291-aa65-8f3d-6f6c-6adf60c39548.tmp
2003-12-07T06:32:30 W. Europe Standard Time INFO xfer from 63.211.151.57:12035 complete: C:\Documents and Settings\bzzt\Application Data\SecondLife\cache\inventory_2eadd291-aa65-8f3d-6f6c-6adf60c39548.tmp
2003-12-07T06:32:39 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:32:42 W. Europe Standard Time INFO LLAvatarTracker::processOnlineNotification()
2003-12-07T06:32:54 W. Europe Standard Time INFO Transmitting sessions stats
2003-12-07T06:33:27 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:34:09 W. Europe Standard Time INFO LLVOAvatar Constructor (0x0E2A0038) id:3d7ce851-3569-c22e-5b85-1ab59e48a0b5
2003-12-07T06:34:09 W. Europe Standard Time INFO Rebuilding avatar: avatar
2003-12-07T06:34:09 W. Europe Standard Time INFO Avatar load took 0.0311477 seconds.
2003-12-07T06:34:09 W. Europe Standard Time INFO getNVPair( AttachItemID ) = 25626c84-8d5b-53a8-a0cb-c4f374d5cf35
2003-12-07T06:34:09 W. Europe Standard Time INFO Attaching object (10) item_id=25626c84-8d5b-53a8-a0cb-c4f374d5cf35 task_id=dce392f4-c776-eb3f-0beb-ae7285a63552to Pelvis
2003-12-07T06:34:09 W. Europe Standard Time INFO 9 msgs decoded, net 0 msgs queued this frame!
2003-12-07T06:34:12 W. Europe Standard Time INFO LLAvatarTracker::processOnlineNotification()
2003-12-07T06:34:42 W. Europe Standard Time INFO Item detached 25626c84-8d5b-53a8-a0cb-c4f374d5cf35
2003-12-07T06:34:42 W. Europe Standard Time INFO Detaching object from Pelvis
2003-12-07T06:34:42 W. Europe Standard Time INFO LLVOAvatar Destructor (0x0E2A0038) id:3d7ce851-3569-c22e-5b85-1ab59e48a0b5
2003-12-07T06:34:42 W. Europe Standard Time INFO LLVOAvatar Destructor end
2003-12-07T06:34:47 W. Europe Standard Time INFO LLAvatarTracker::processOnlineNotification()
2003-12-07T06:34:57 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:35:59 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:36:06 W. Europe Standard Time INFO packet_out_of_order - got packet 8213 expecting 8214
2003-12-07T06:36:06 W. Europe Standard Time INFO packet_out_of_order - got packet 8213 expecting 8214
2003-12-07T06:36:06 W. Europe Standard Time INFO packet_out_of_order - got packet 8213 expecting 8214
2003-12-07T06:36:43 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:36:45 W. Europe Standard Time INFO packet_out_of_order - got packet 36138 expecting 36139
2003-12-07T06:36:58 W. Europe Standard Time INFO LLAvatarTracker::processOfflineNotification()
2003-12-07T06:37:54 W. Europe Standard Time INFO Transmitting sessions stats
2003-12-07T06:37:59 W. Europe Standard Time INFO LLAvatarTracker::processOnlineNotification()
2003-12-07T06:39:23 W. Europe Standard Time INFO packet_out_of_order - got packet 67 expecting 8560
2003-12-07T06:39:26 W. Europe Standard Time INFO Circuit: 63.211.151.57:12035 resent 20 packets
2003-12-07T06:39:56 W. Europe Standard Time INFO Circuit: 63.211.151.57:12035 resent 43 packets
2003-12-07T06:40:10 W. Europe Standard Time INFO About to drop 63.211.151.55:12035 after alive timeout reached 10.0092 seconds.
2003-12-07T06:40:14 W. Europe Standard Time INFO About to drop 63.211.151.56:12035 after alive timeout reached 10.0149 seconds.
2003-12-07T06:40:14 W. Europe Standard Time INFO About to drop 63.211.151.57:12035 after alive timeout reached 10.015 seconds.
2003-12-07T06:40:20 W. Europe Standard Time INFO About to drop 63.211.151.55:12035 after alive timeout reached 10.0095 seconds.
2003-12-07T06:40:24 W. Europe Standard Time INFO About to drop 63.211.151.56:12035 after alive timeout reached 10.0075 seconds.
2003-12-07T06:40:24 W. Europe Standard Time INFO About to drop 63.211.151.57:12035 after alive timeout reached 10.0076 seconds.
2003-12-07T06:40:27 W. Europe Standard Time INFO Circuit: 63.211.151.57:12035 resent 39 packets
2003-12-07T06:40:30 W. Europe Standard Time WARNING Dropping unresponsive circuit: 63.211.151.55:12035 after alive timeout reached 10.0201 seconds.
2003-12-07T06:40:30 W. Europe Standard Time WARNING sendMessage - Trying to send message StillAlivePing to dead circuit 63.211.151.55:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING Dropping unresponsive circuit: 63.211.151.56:12035 after alive timeout reached 10.0011 seconds.
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message StillAlivePing to dead circuit 63.211.151.56:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING Dropping unresponsive circuit: 63.211.151.57:12035 after alive timeout reached 10.0012 seconds.
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message StillAlivePing to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035
2003-12-07T06:40:34 W. Europe Standard Time WARNING sendMessage - Trying to send message AgentUpdate to dead circuit 63.211.151.57:12035

Note how all 3 sim connections (I was near a 3-sim corner) timeout, but not the userserver. This is the part that puzzles me.

My SL machine is behind a router using NAT, and this setup has been working reliably before. I'm not sure if this started with 1.1.9, but it might have.