ip확인시 eth0,lo외에 sit0은 뭔가요?

#ifconfig -a 했을때 'sit0'이라고 나오는데

뭔지 모르겠습니다.

eth0      Link encap:Ethernet  HWaddr 00:0C:29:BE:CD:C0

...................(생략)

lo        Link encap:Local Loopback

...................(생략)

sit0      Link encap:IPv6-in-IPv4
          NOARP  MTU:1480  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

.../network-scripts/ 디렉토리내에도...ifcfg-eth0, ifcfg-lo는 있는데 sit0관련된것은 없습니다.

sit0 ?