I seem to have an issue with IP queue.

I have a linux machine that I am using to run some experiments. The linux machine is configured to be a router, having two NICs, connecting two other computers, and managing their network traffic. All incoming packages are captured, using iptables, and analyzed by a C application.

The application analyzing the packets has a built-in delay, as part of the experiment.

So I have one very fast computer sending packets through my linux-router and a (relatively) slow linux-router that analyses and deals with the packets, one by one.

This situation leads to the fact that when I fire up a sender application on one of the computers connected to the linux-router, my IP queue on the linux-router gets filled up (almost) instantaneously.

The IP queue's max length is currently set to 1024, and if it overflows, the packets are dropped. This is expected and i'm OK with it.

But, (and this is where it gets interesting), every now and then I get the following error:

"Failed to receive netlink message: No buffer space available"

At start, I thought this was due to the IP queue overflow, but after some analysis i found that sometimes I get the error even if the IP queue buffer did not overflow, and sometime I DON'T get the message even though the buffer DID overflow.

When I run > cat /proc/net/ip_queue, I get the following table (also used to monitor the IP queue overflow):

Peer PID          : 27389
Copy mode         : 2
Copy range        : 65535
Queue length      : 0
Queue max. length : 1024
Queue dropped     : 1166875
Netlink dropped   : 2916

Looking at the last two values, Queue dropped seems to refer to packets that did not manage to get into the IP queue because the buffer was full. I can see this value rise as I bombard the linux-router. Netlink dropped ( as it's name implies :) ) seems to have to do with the error i'm getting.

I did my best to search for material on this error, but wasn't able to find anything that seemed to point me in the required direction.

Bottom line: Why am I getting this error and what can I do to avoid it?