extensions that contain options for destination processing. If the router is an intermediate node,
IPv6 examines the header extensions that contain forwarding options.
By examining only the extension headers that apply to the operations it performs, IPv6 reduces
the amount of time and processing resources required to process a packet.
IPv6 defines the following extension headers:
• The hop-by-hop extension header contains optional information that all intermediate IPv6
routers examine between the source and the destination.
• The end-to-end extension header contains optional information for the destination
node.
• The source routing extension header contains a list of one or more intermediate nodes
that define a path for the packet to follow through the network, to its destination. The
packet source creates this list. This function is similar to the IPv4 source routing
options.
• An IPv6 source uses the fragment header to send a packet larger than fits in the path
maximum transmission unit (MTU) to a destination. In order to send a packet that is too
large to fit in the MTU of the path to a destination, a source node can divide the packet
into fragments and send each fragment as a separate packet, to be reassembled at the
receiver.
• The authentication extension header and the security encapsulation extension header,
used singly or jointly, provide security services for IPv6 datagrams.
Comparison of IPv4 and IPv6
The following table compares key dif
ferences between IPv4 and IPv6.
T
able 5: IPv4 and IPv6 differences
Feature IPv4 IPv6
Address length 32 bits 128 bits
IPsec support
1
Optional Required
QoS support Limited Improved
Fragmentation Hosts and routers Hosts only
Minimum MTU (packet size) 576 bytes 1280 bytes
Checksum in header Yes No
Options in header Yes No
Link-layer address resolution ARP (broadcast) Multicast Neighbor
Discovery Messages
IPv6 management
Configuration — System April 2011 33
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