P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

PReP · 2014-09-05 13:26:23

Lately i have had a hard, or more or less impossible, time dealing with p2p (torrent) downloads.

I use qbittorrent for instance, same config as i have for years, and even when only dealing with 1 single torrent i soon get a stalled internet.

dmesg shows this:

[ 1827.309029] TCP: TCP: Possible SYN flooding on port xxxxxx. Dropping request.  Check SNMP counters. 
[ 1946.897273] TCP: TCP: Possible SYN flooding on port xxxxxx. Dropping request.  Check SNMP counters.
[ 5788.100712] DCCP: Activated CCID 2 (TCP-like)
[ 5788.100722] DCCP: Activated CCID 3 (TCP-Friendly Rate Control)
[ 6520.138703] r8169 0000:04:00.0 eth0: link down
[ 6541.652164] r8169 0000:04:00.0 eth0: link up
[ 6690.172294] r8169 0000:04:00.0 eth0: link down
[ 6705.719074] r8169 0000:04:00.0 eth0: link up
[14489.083658] perf interrupt took too long (2507 > 2495), lowering kernel.perf_event_max_sample_rate to 50100
[20537.730207] TCP: TCP: Possible SYN flooding on port xxxxxx. Dropping request.  Check SNMP counters.

I have read about syn flooding and torrents triggering it, and i have tried:

Lowering number of connections massively in qbittorrent,
having the sysctl setting: net.ipv4.tcp_syncookies = 0/1 toggled,
and just about anything i can think off.

I have also tried googling and searching the net to the best of my (however good or bad) ability.

- Is this some sort of new kernel behaviour that i need to read up to, or is something else bonkered in my trusty arch install?

DCCP: CCID (TCP-Friendly Rate Control) - stands out to me, what is this doing, because of the syn flooding?
Is that the thing that puts my connection to a grinding halt after a few moments?
Can we configure that somehow?

as do the eth0 link down and up (not triggered by me)

It _looks_ to me as some sort of new protection/automation thing, that might make the wrong call on my part?

Do anyone else have new experience with p2p transfers killing the bandwidht and choking the internet as a whole?
(The old limiting UP and DL or number of connections in the software does not seem to help at all.)

Last edited by PReP (2014-09-28 22:22:20)

schnoopay · 2014-09-07 02:57:52

I don't have a solution but I can confirm I've been having the same issue recently, although I use utserver with a proxy. Again, haven't changed the config in utserver.

Soukyuu · 2014-09-07 20:57:30

I've been having similar problems (stalled internet) with qbittorrent and for some reason it is only happening if I do not limit my upload bandwidth in qbittorrent.
With µtorrent (wine), it was even worse - my router crashed and rebooted within a few hours of µtorrent running.

Once I've limited my upload to slightly below my actual upload bandwidth, all problems stopped.

Last edited by Soukyuu (2014-09-07 20:58:01)

schnoopay · 2014-09-09 03:48:04

I already had my torrent upload speed set a bit below my maximum speed, but was still having problems, although previously having it set to unlimited would cause my internet experience to suffer greatly.

I did just try setting my "max half open connection limit" to 80 instead of the previous 250 and it seems to be working much as it was before. I can still browse the web and download from ftp at acceptable speeds, DNS isn't timing out etc. As I said, I was using utserver from AUR, so I don't know if this will help or not but give it a look.

PReP · 2014-09-24 10:41:49

Hello all, i just wanted to chime in again, even if it is without any real "solution"

Currently things seem to be working alright again, unfortunately with a greatly limited Upload bandwidht setting.
I don't know if this is what "fixed" it, or if it was just the stars and package-version aliging in the right positions at this time.

But i think i tried bandwidht limiting before aswell without change, so i am not sure if the underlying issue is resolved.
Then again, it seems only a few of us suffers from this, so it might be something specific to our use-cases *shrugs shoulders*

At any rate i thank you all for your input and advices anyways!
- Props to the arch community as usual

HiImTye · 2014-09-24 23:34:18

I haven't experienced this with Deluge, but I limit my upload with tc and iptables, and prioritize traffic, so it likely is stopped before it's an issue

schnoopay · 2014-09-25 07:28:57

I'm currently playing with tc to see what I can manage with it. Turns out that the newer versions of libtorrent-rasterbar actually work with my torrent proxy, so I'd like to switch over to deluge. I currently have tc set up where my non-torrent downloads are both fairly evenly balanced and aren't killed by uploads by following lartc.org's howto. My next step is to try and get all my torrent traffic to be lower priority, despite being made up of numerous connections, as torrent traffic still gets way too high a priority and kills the download speeds of anything else.

HiImTye · 2014-09-25 07:36:38

here's my torrent rule for reference

# * high priority server class * #
# mark 7 #
# bittorent
iptables -A OUTPUT -t mangle -p tcp --match multiport --dport 6881:6891 -j MARK --set-mark 7

Last edited by HiImTye (2014-09-25 07:40:21)

PReP · 2014-09-28 22:21:35

Thanks HilmTye, i hadn't thought about using iptables to get a more generally "controlled" way of keeping that traffic in line,
worth to look into if my issue arises again

Last edited by PReP (2014-09-28 22:21:48)

HiImTye · 2014-09-28 22:43:59

yeah, netfilter/iptables is extremely useful, more so than most people realize. there really is no substitute for learning iptables. you should take the time to learn them, even if you use another solution, such as UFW, because it gives you a much greater area of control, especially if you need to mitigate some issues before your UFW rules. anyway, that rule marks torrent traffic with mark 7, which should be defined with tc to control speed. you should definitely check out the wealth of knowledge at lartc, and spend some time on Google after for some more recent stuff.

PReP · 2014-09-29 12:35:02

For sure. I have setup "basic" iptables for closed and open ports, but haven't looked into it further so this both helps me solve a problem as well as learning a bit more of it's power, so win win.

Though i still want to look up what is happening with the actuall warnings in the log and what that is about later

Arch Linux

#1 2014-09-05 13:26:23

P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#2 2014-09-07 02:57:52

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#3 2014-09-07 20:57:30

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#4 2014-09-09 03:48:04

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#5 2014-09-24 10:41:49

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#6 2014-09-24 23:34:18

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#7 2014-09-25 07:28:57

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#8 2014-09-25 07:36:38

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#9 2014-09-28 22:21:35

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#10 2014-09-28 22:43:59

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

#11 2014-09-29 12:35:02

Re: P2P (Torrents) > Syn Flood > DCCP > Internet Stalled [Workaround?]

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