Lots of Flushing x bytes to y would block messages

[Guus Sliepen]

On Wed, May 04, 2016 at 07:10:47AM +0800, Terry T wrote:

> We run tinc in a linux environment in which it sits there waiting for
> connections from the clients. All clients are configured to only have one
> ConnectTo which points to this server.
> 
> We're seeing in the server log that as soon as a client's connection is
> activated, a whole bunch of "Flushing x bytes to that host would block" is
> logged and the whole vpn is bogged down and has become non-responsive.

This means that the bandwidth to that client is so low that the TCP
buffer on the server is full. It should not cause communication between
the other clients to slow down though...

> From a Jun 27, 2013 "Metadata socket read error" thread, Gus suggested that
> it may be caused by the router in front of the server that ran out of
> memory keeping track of the outgoing connections. The server is indeed
> behind a NAT router. It's a reasonably (ASUS) high end consumer grade
> router.

This is not the same problem.

> We have tried adding PingInterval in the host configuration file, but it
> doesn't seem to resolve the problem. Is there anything else that we can do
> to stop the vpn from crashing. As it is, when any one of the client is
> logged to be flushing, the whole vpn becomes unusable.

Hm, does non-VPN traffic to/from the server also get slow when this
happens?

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>