high cpu load with tcpdump

[6bone%6bone.informatik.uni-leipzig.de@localhost]

Hello,

On my router tcpdump uses always 100% CPU.

  PID USERNAME PRI NICE   SIZE   RES STATE      TIME   WCPU    CPU COMMAND
 3403 _tcpdump  38    0    19M 3016K RUN/6      0:24 98.08% 70.02% tcpdump
    0 root       0    0     0K 1182M CPU/7     49:35  0.00%  3.76% [system]

The problem also occurs when tcpdump is listening on an interface 
with no network traffic. Therefore, it can not be a load problem.

The problem does not occur on all interfaces.

ixg(0|1), bnx(0|1) and tap(0|1) are affected.

lo0, stf0 and vlan* are not affected.


System is: NetBSD 7.0_STABLE

Any idea what could be the problem?


Thank you for your efforts.


Regards
Uwe