IPv6 Essentials

Chapter 9. Upper-Layer Protocols

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 DNS can return either an IPv4 or an IPv6 address to make the IP protocol fully transparent.

UDP/TCP

Checksumming is done on different layers. Remember, the IPv6 header does not have a checksum. But a checksum is important on the transport layer to determine misdelivery of packets. Other upper-layer protocols may use a checksum, too. All checksum calculations that include the IP address in the calculation must be modified for IPv6 to accommodate the new 128-bit address.

Transport protocols like UDP and TCP attach checksums to their packets. A checksum is generated using a pseudoheader. The TCP and UDP pseudoheader for IPv6 contains fields for source and destination address, payload length, and next header value (RFC 2460). If the IPv6 packet contains a routing header, the destination address used in the pseudoheader is the address of the final destination. If the source or ...