udp port 3 - what's that?

Hi SuSErs, What is udp port 3 for? /etc/services names it as compressnet. The reason I'm asking is that I keep getting lots of messages in my log like: Apr 21 15:40:43 fizia kernel: Packet log: output DENY eth0 PROTO=1 x.x.x.x:3 y.y.y.y:3 L=95 S=0xC0 I=0 F=0x4000 T=255 (#3) As I interpret it, some process on my machine tries to send a UDP packet from port 3 to port 3 on some host on ISP network. Firewall rules deny this. I wonder what process may try these connections? My machine connects ver Ethernet to an ADSL modem, if it is relevant. I found some messages about this weird compressnet in German list but can understand nothing from them. Could anyone shed some light? Thanks, -Kastus