[ipxe-devel] [PATCH] [tcp] Send keepalive packets to prevent TCP stalls

[Gerd Hoffmann]

  Hi,

> > OK, but in that situation we don't expect traffic to get through anyway;
> > it's a broken setup.
> 
> Yes, there definitely has to be something broken about the network
> setup for this to make a difference. Unfortunately, and please excuse
> my pragmatism, that's often the reality and finding/fixing the root
> cause may be prohibitively hard.

Indeed, and even if you find the root cause it might not be easily
fixable, for example in case it is some firmware bug.

I actually see something simliar on my wifi network @home.  Some small
arm boards are running here, hooked up to the network over wireless.
Sometimes ssh-ing into those boards simply doesn't work.  Then go login
on the console, try figure what is going on, everything looks fine.  And
as soon as I generate some outbound network traffic (ping default
gateway for example) incoming ssh starts working.  Huh?

I still didn't figure the root cause for this.  No NAT involved.  No
duplicate MAC addresses.  dhcpd hands out fixed ip addresses.

Suspecting the wifi access points, as it doesn't happen for
ethernet-connected devices.

Current workaround: enable ntpd, to generate some low-bandwidth outgoing
traffic (and b/c some of those boards don't have a real time clock).
Simliar to what this patch does.

cheers,
  Gerd