The Next header field is a 1-bytedata field in the IPv6 protocol header. It specifies the header type that follows the IPv6 header.
The Next header field identifies either the first extension header, if any, or upper layer protocols, such as TCP, UDP, or ICMPv6. If the Next header field identifies a protocol above the network layer, then the code values of the data field correspond to those in the IPv4 protocol.
For example, if the Next header data field is coded 0, then the following header is for IPv4. If it is coded 1, it is for Internet Control Message Protocol( ICMP) under IPv4, if it is coded 2, it is for Internet Group Management Protocol ( IGMP) under IPv4, a 6 represents Transmission Control Protocol (TCP), the 17 represents User Datagram Protocol (UDP), the 58 represents Internet Control Message Protocol (ICMP) under IPv6, and the 89 represents Open Shortest Path First( OSPF).