5.3 IPv6 Packet Flashcards
IPv6
IPv6 overcomes the limitations of IPv4 and is a powerful enhancement with features that better suit current and foreseeable network demands.
Improvements that IPv6 provides include the following:
1 Increased address space - IPv6 addresses are based on 128-bit hierarchical addressing as opposed to IPv4
with 32 bits.
2 Improved packet handling - The IPv6 header has been simplified with fewer fields.
3 Eliminates the need for NAT - With such a large number of public IPv6 addresses, NAT between a private IPv4
address and a public IPv4 is not needed. This avoids some of the NAT-induced
problems experienced by applications that require end-to-end connectivity.
The 32-bit IPv4 address space provides approximately 4,294,967,296 unique addresses.
IPv6 address space provides 340 undecillion addresses.
IPv6 PACKET HEADER
The fields in the IPv6 packet header include the following:
Version - This field contains a 4-bit binary value set to 0110 that identifies this as an IP version 6 packet.
Traffic Class - This 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field.
Flow Label - This 20-bit field suggests that all packets with the same flow label receive the same type of handling
by routers.
Payload Length - This 16-bit field indicates the length of the data portion or payload of the IPv6 packet. This does
not include the length of the IPv6 header, which is a fixed 40-byte header.
Next Header - This 8-bit field is equivalent to the IPv4 Protocol field. It indicates the data payload type that the
packet is carrying, enabling the network layer to pass the data to the appropriate upper-layer
protocol.
Hop Limit - This 8-bit field replaces the IPv4 TTL field. This value is decremented by a value of 1 by each router
that forwards the packet. When the counter reaches 0, the packet is discarded, and an ICMPv6 Time
Exceeded message is forwarded to the sending host,. This indicates that the packet did not reach its
destination because the hop limit was exceeded. Unlike IPv4, IPv6 does not include an IPv6 Header
Checksum, because this function is performed at both the lower and upper layers. This means the
checksum does not need to be recalculated by each router when it decrements the Hop Limit field,
which also improves network performance.
Source IPv6 Address - This 128-bit field identifies the IPv6 address of the sending host.
Destination IPv6 Address - This 128-bit field identifies the IPv6 address of the receiving host.
An IPv6 packet may also contain extension headers (EH), which provide optional network layer information. Extension headers are optional and are placed between the IPv6 header and the payload. EHs are used for fragmentation, security, to support mobility and more.
Unlike IPv4, routers do not fragment routed IPv6 packets.
