The impact of IPv6 on upper-layer protocols is minimal because the datagram service has not changed substantially. This chapter discusses UDP and TCP over IPv6 and describes changes for upper-layer protocols, such as DNS, DHCP, SLP, FTP, Telnet, and HTTP when used over IPv6. The most important changes are always needed where an IP address is used. Any process or application that uses an IP address needs to be updated to be able to handle the extended 128-bit address format. Applications that use a hardcoded 32-bit IPv4 address should be updated to use a DNS name instead, so that DNS can return either an IPv4 or an IPv6 address to make the IP protocol fully transparent.