Network drops after 10 minutes of moderate activity

palswim · Thu Jan 15, 2015 2:28 am

Model: B (512 MB RAM)
Distribution: XBian 1.0 RC2

My Raspberry Pi functions mainly as a server for my files, hosing various services such as FTP, rsync, samba, etc. I have configured my router (DD-WRT) and ISP (AT&T U-Verse) so that I can access my server from the Internet. I have found that, with a high degree of consistency, any transfers I initiate from an external source (transferring the bulk of the data from the Pi server to the client) will time out after ten minutes of activity.

My ISP limits my upload bandwidth to 2Mb/s (I see it top out around 240kB/s), so I can transfer about 140MB of data before the connection drops. I have tried to reproduce this within my LAN which contains the Pi, by limiting my bandwidth in the FTP/rsync clients, but I cannot. Also, I can maintain SSH (shell, haven't tried tunnel) connections indefinitely, even through the drops.

The results of my tests (mainly transferring the same 1 GB file):
Success means that the file transferred without issue; Drop means the connection dropped after about ten minutes

WAN Test 1
- Source: Pi, pure-ftpd
- Destination: External Client 1
- Result: Drop
WAN Test 2
- Source: Pi, rsync
- Destination: External Client 1
- Result: Drop
LAN Test 1
- Source: Pi, pure-ftpd
- Destination: Internal Client
- Result: Success
LAN Test 2
- Source: Pi, rsync
- Destination: Internal Client
- Result: Success
LAN Test 3
- Source: Pi, pure-ftpd
- Destination: Internal Client
- Note: Limited bandwidth to 300 kB/s
- Result: Success
LAN Test 4
- Source: Pi, rsync
- Destination: Internal Client
- Note: Limited bandwidth to 300kB/s
- Result: Success
WAN Test 3
- Source: Pi, pure-ftpd
- Destination: External Client 2
- Result: Drop
WAN Test 4
- Source: Pi, rsync
- Destination: External Client 2
- Result: Drop
WAN Test 5
- Source: External Client 1
- Destination: Pi, pure-ftpd
- Result: Success
WAN Test 6
- Source: External Client 1
- Destination: Pi, rsync
- Result: Success
WAN Test 7
- Source: External Client 1
- Destination: Pi, pure-ftpd
- Note: Limited bandwidth to 300 kB/s
- Result: Success
WAN Test 8
- Source: Internal Windows 7 - Filezilla FTP Server
- Destination: External Client 1
- Result: Success
WAN Test 9
- Source: Internal Windows 7 - cygwin rsync
- Destination: External Client 1
- Result: Success
WAN Test 10
- Source: Pi, rsync
- Destination: External Client 1
- Note: Limited bandwidth to 80kB/s
- Result: Success

Some of these test results may surprise you, as they did me, and maybe some of the results happened for non-obvious reasons (like the bandwidth-limiting algorithms don't quite match a hard ISP limit). Initially, I blamed my ISP, but after repeated download failures from the Pi and repeated download successes from a test Windows server, I can't confidently blame AT&T (ISP) any more.

I have tried altering power supplies, but the Pi has never restarted or even dropped all networking, so this seems like some driver/hardware/USB issue, of which I have seen reports around the web.

How would I even begin to solve/fix this?