02-02-2013, 01:02 PM
IPv6 Packet Format
IPv6 Packet.ppt (Size: 491.5 KB / Downloads: 456)
IP Frame
IP packets are carried over link-layer technologies such as Ethernet (10 Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1000 Mbps), Frame Relay, and many others.
Each link-layer technology family has its own link-layer frame that carries IP packets.
IP packet is carried between the frame header and frame trailer of a link-layer frame.
IP Packet
An IP packet has two fundamental components:
IP header
IP header contains many fields that are used by routers to forward the packet from network to network to a final destination.
Contains layer 3 info
Fields within the IP header identify the sender, receiver, and transport protocol and define many other Parameters.
Payload
Represents the information (data) to be delivered to the receiver by the sender.
Contains data & upper-layer info
IPv4 Header - Review
Time to Live ( 8 bits)
Indicate the maximum number of links on which an IPv4 packet can travel before being discarded.
Originally used as a time count with which an IPv4 router determined the length of time required (in seconds) to forward the IPv4 packet, decrementing the TTL accordingly. Modern routers almost always forward an IPv4 packet in less than a second and are required by RFC 791 to decrement the TTL by at least one. Therefore, the TTL becomes a maximum link count with the value set by the sending node. When the TTL equals 0,an ICMP Time Expired-TTL Expired in Transit message is sent to the source IPv4 address and the packet is discarded.
Protocol (8 bits)
Identifies the upper layer protocol.
For example, TCP uses a Protocol of 6, UDP uses a Protocol of 17, and ICMP uses a Protocol of 1.
The Protocol field is used to demultiplex an IPv4 packet to the upper layer protocol.
IPv6 Header Fields
Based on these rules, RFC 2460 defines the following IPv6 header fields:
Version (4 bits)
4 bits are used to indicate the version of IP and is set to 6
Traffic Class (8 bits)
same function as the Type of Service field in the IPv4 header.
Flow Label (20 bits)
identifies a flow and it is intended to enable the router to identify packets that should be treated in a similar way without the need for deep lookups within those packets.
set by the source and should not be changed by routers along the path to destination.
unique & powerful tool to IPv6
Can be used with differentiated services (DiffServ) as well as integrated services (IntServ) and Resource ReSerVation Protocol (RSVP2).
IPv6 Next Header (Extension)
RFC 2460 defines the following IPv6 extension headers that must be supported by all IPv6 nodes:
Hop-by-Hop Options header
Destination Options header
Routing header
Fragment header
Authentication header
Encapsulating Security Payload header