ral0 interface hangs with the message "No buffer space available"

[Yuri]

Almost every time when I leave system to download a large file I get ral 
device inoperable after a while.
Pinging the other peer causes these messages:

 > ping 192.168.0.1
PING 192.168.0.1 (192.168.0.1): 56 data bytes
ping: sendto: No buffer space available
ping: sendto: No buffer space available

I don't believe that TCP buffer is legitimately filled up to the max 
because after I bring it down and back up it works fine for a long 
while. So why didn't this data go through before down/up?

If TCP connections are slow buffers shouldn't just fill up: system can 
and should be preventing this letting apps to hold data streams.

Something isn't quite right.

Why would network device hang in a steady download scenaio?

7.2-STABLE

Yuri