I found that gateway I use, sometimes receives packets from my FreeBSD 5.3 box with ttl 63. But when I dumped tcp packets (with tcpdump) that are send from my computer, they always got ttl 64. Moreover Linux (Fedora Core 2) running on same computer don't have such problems. Also older versions of FreeBSD (5.2.1 for example) work fine (ttl's are correct). It's specially important for me, because my ISP, that owns gateway, use simple method to check if he have illegal clients - firewall on gateway drops packets with odd ttl.