Configuration Guide Configuring IPv6
Payload Length
This field consists of 16 bits, including the packet payload length and the length of IPv6 extended options (if available).
That is, it includes the IPv6 packet length except the IPv6 packet header.
Next Header
This field indicates the protocol type in the header field following the IPv6 packet header. Similar to the Protocol field in the
IPv4 address header, the Next Header field is used to indicate whether the upper layer uses TCP or UDP. It can also be
used to indicate existence of the IPv6 extension header.
Hop Limit
This field consists of 8 bits. Every time a device forwards a packet, the field value reduced by 1. If the field value reaches 0,
this packet will be discarded. It is similar to the Lifetime field in the IPv4 packet header.
Source Address
This field consists of 128 bits and indicates the sender address in an IPv6 packet.
Destination Address
This field consists of 128 bits and indicates the receiver address in an IPv6 packet.
At present, IPv6 defines the following extension headers:
Hop-By-Hop Options
This extension header must follow the IPv6 packet header. It consists of option data to be checked on each node along
the path.
Routing Options (Type 0 routing header)
This extension header indicates the nodes that a packet passes through from the source address to the destination
address. It consists of the address list of the passerby nodes. The initial destination address in the IPv6 packet header is
the first address among the addresses in the routing header, but not the final destination address of the packet. After the
node corresponding to the destination address in the IPv6 packet header receives a packet, it processes the IPv6 packet
header and routing header, and sends the packet to the second address, the third address, and so on in the routing
header list till the packet reaches the final destination address.
Fragment
The source node uses this extension header to fragment the packets of which the length exceeds the path MTU (PMTU).
Destination Options
This extension header replaces the option fields of IPv4. At present, the Destination Options field can only be filled with
integral multiples of 64 bits (eight bytes) if required. This extension header can be used to carry information to be checked
by the destination node.
Upper-layer header
This extension header indicates the protocol used at the upper layer, such as TCP (6) and UDP (17).
Another two extension headers AH and ESP will be described in the Configuring IPSec.
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