what is the multicast doing on 224 0 0 251

Question

On my debian server  squeeze  I get this message every few seconds      Sep 18 21 28 14 myhost kernel   7903784 720091  AIF UNPRIV connect   attempt  IN eth0 OUT  MAC  SRC my serverip eth0 DST 224 0 0 251   LEN 72 TOS 0x00 PREC 0x00 TTL 255 ID 0 DF PROTO UDP SPT 5353 DPT 5353   LEN 52   the packets are coming from inside my server  i replaced it with my serverip eth0  and seem to be blocked going out to the destination 224 0 0 251   So some task inside my server is contacting 224 0 0 251 and this is blocked by my arnos firewall   How can I find out who or which task is trying to do that and if it is useful or not   And if I don t need it  how can I suppress that message then

User · Answer

I deactivated my  Arno s Iptables Firewall  for testing  and then the messages are gone

User · Answer

If you don t have avahi installed then it s probably cups

User · Answer

Those look much like Bonjour   mDNS requests to me  Those packets use multicast IP address 224 0 0 251 and port 5353   The most likely source for this is Apple iTunes  which comes pre-installed on Mac computers  and is a popular install on Windows machines as well   Apple iTunes uses it to discover other iTunes-compatible devices in the same WiFi network   mDNS is also used  primarily by Apple s Mac and iOS devices  to discover mDNS-compatible devices such as printers on the same network   If this is a Linux box instead  it s probably the Avahi daemon then  Avahi is ZeroConf Bonjour compatible and installed by default  but if you don t use DNS-SD or mDNS  it can be disabled

[dns] what is the multicast doing on 224.0.0.251?

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