If you're looking to send Syslog, you don't need to craft custom UDP packets. You can use IO::Socket to create TCP and UDP packets without worrying about checksum calculation - it's done for you by the OS IP/socket stack.

For Syslog specifically, just use Net::Syslog. You don't even need to worry about sockets with that - it's done behind the scenes.

If you need to listen to / receive Syslog messages, have a look at Net::Syslogd.