[Bug 945] New: Transmit performance regression with NAT and 3.14

bugzilla-daemon at netfilter.org bugzilla-daemon at netfilter.org
Wed May 21 19:28:01 CEST 2014


           Summary: Transmit performance regression with NAT and 3.14
           Product: netfilter/iptables
           Version: unspecified
          Platform: x86_64
               URL: http://www.linuxquestions.org/questions/linux-networki
        OS/Version: other
            Status: NEW
          Severity: major
          Priority: P3
         Component: NAT
        AssignedTo: netfilter-buglog at lists.netfilter.org
        ReportedBy: rpower at sysreset.com
   Estimated Hours: 0.0

The short version is I have a Linux router running PPPoE on a DSL modem in
bridge mode. This is a Slackware64 machine.  

Everything works great on the router itself but the problem is anything else on
the LAN using this machine as a router has crap upload performance.  WAN
downloads via the LAN are unimpaired and run at the maximum DSL speed.  Uploads
from the router itself will hit ~550KBps.  Uploads from any other machine on
the LAN to the WAN struggle to exceed 10KBps.  Wireshark/tcpdump show a massive
number of retransmits on client machines, but only when trying to send data
over the WAN.  Oddly none of these retransmit packets seem to be passing though

Transfers to and from the router over the local LAN will hit the line speed, so
it's not related to the switch or eth0. On a whim I've also replaced the
network cards in several machines as well as the switch to no avail. Turning
off network offload on all devices has no impact as well. The MTU is set the
same on all devices.

I've tried a couple different kernel versions, and I'm fairly certain the
change that broke things was in 3.14.0.

Currently I've tested the following:
3.10.40: OK
3.12.20: OK
3.13.11: OK
3.14.0: FAIL
3.14.4: FAIL

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