The 
Tcl core has supported 
TCP sockets via 
socket since version 7 or so, but 
UDP must be supplied by an 
extension.
 See Also  edit
- UDP in the Tcl core
 UDP Protocols  edit
- Trivial FTP
 Tcl UDP Extensions  edit
The following extensions provide UDP support:
- TclUDP
- The normal package for standard UDP client/server programs.  It is quite simple to use.
- Tcl-dp
- An extensive TCP/IP package which also supports UDP
- Scotty
- An SNMP package with its own UDP implementation
- pktsrc
- Access to raw IP Datagram and thus to UDP
- ceptcl
- Communications EndPoints for Tcl
- Packet
- A few Tcl routines for manipulating network packets
- UDP extension
- a small and clean critcl-based extension written in 2011 by CMcC
- Duft
- Datagrams and Udp For Tcl
 UDP enabled packages  edit
PT: The 
dns package in 
tcllib is capable of using udp if available.  So are the 
time and 
ntp packages.