Nginx / LRO on vmxnet3 / missing ACKs

Lukas Tribus luky-37 at
Tue Jan 12 11:07:25 UTC 2016

> Hello,
> I'm currently investigating an issue with Linux (3.13.0), nginx (1.6.2),
> vmxnet3 (, IPv6 connections and large receive offload (LRO)
> enabled. The workflow we are investigating is a POST of a small file (jpg)
> towards a php5-fpm pool.
> From a network (tcpdump) point a view, it seems that when LRO is disabled on
> the vmxnet3 interface, all tcp packets are ack'ed correctly after reception.
> However, when LRO is enabled, only the request part of the POST is acked at
> tcp-level before the client retransmits the packets.

This is clearly not a userspace issue. Its either a kernel or a hypervisor issue.

I would start by using a supported and uptodate kernel, because 3.13.0 is neither.


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