IPv6
- IPv6 is the solution for many limitations in IPv4. However, IPv6 is not yet vastly deployed due
to the overwhelming tasks of readdressing and upgrading of existing networks and applications.
- Below are some benefits of implementing IPv6:
i) Larger address space provides better support for more granular hierarchical addressing,
greater number of addressable nodes, and simpler autoconfiguration of addresses.
ii) The simpler and fixed-size header enables better routing efficiency and performance.
iii) Various transition mechanisms, eg: dual stack, tunneling, and translation allow existing
IPv4 networks to coexist with IPv6 features.
iv) Provides native support for new mobility and security standards – Mobile IP and IPsec.
v) Security and QoS can be implemented more efficiently with end-to-end connectivity
instead of intermediate address translations (IPv6 eliminates the need for deploying NAT).
- Mobility provides roaming service for mobile devices (eg: IP phones) without interrupting the
current connection. Mobile IP is available for both IPv4 (as an add-in) and IPv6 (built-in).
- IPsec ensures better security (integrity, authentication, and confidentiality) for IPv6 networks.
It is available for IPv4 and is mandatory for IPv6 – it is enabled and available on all IPv6 nodes.
IPsec support and implementation is a mandatory part of IPv6 but is not an integral part of IPv4.
However, due to the slow uptake of IPv6, IPsec is commonly used to secure IPv4 traffic.
- A node is a device that implements IPv6, be it a host or a router.
A host is a node that is not a router.
A link is equivalent to a network or a broadcast domain.
A prefix is equivalent to a subnet.
IPv6 Header Format
- The IPv6 header has been simplified to have fewer fields for easier, faster and efficient packet
processing, enhanced performance, and routing efficiency.
- With the design and implementation of the fewer fields and 64-bit aligned fields, IPv6 is able to
take advantage of the upcoming 64-bit processors for faster and efficient processing.
- IPv6 basic header has a fixed length of 40 bytes.
- Since most current link-layer technologies are relatively reliable and perform error detection,
the IP header checksum is considered redundant and hence has been removed. Without the IP
header checksum, both the connection and connectionless transport layer protocols are required
to perform error detection and recovery. The removal of the IP checksum field further reduces
the network layer processing time, as routers can concentrate solely on forwarding packets.
- If checksuming is required, it can be done via an AH header which provides cryptographically
strong authentication and eventually a checksum for the whole packet.
IPv6 Extension Headers
- Instead of having the Options field as in IPv4 header, IPv6 attaches extension headers to the end
of a basic or extension header, with the 8-bit Next Header field specifying the next extension
header if any. The use of extension headers allows faster processing and protocol evolution.
- Extension headers are 64-bit in length and the number of extension headers in an IPv6 packet is
variable. Extension headers are daisy-chained one after another with the Next Header field of
the previous basic or extension header specifies the current extension header. The last extension
header (or the basic header if extension header is not used) has a Next Header field specifies a
transport layer protocol, eg: TCP, UDP.
- The use of extension headers allows end-to-end security, as no firewalls and NAT are involved.
- Mobility provides roaming service for mobile devices (eg: IP phones) without interrupting the
current connection. The IPv6 routing header allows an end system to change its source IP address
with a stable home address, and hence allows the roaming address to maintain mobility.
- Cisco IOS Mobility IP is a tunneling-based solution that uses Cisco GRE or IP-in-IP tunnel.
Tunneling allows a router on a device’s home subnet to transparently forward IP packets to the
roaming devices. IPv4 offers Mobile IP via triangle routing, where data is tunneled back to the
home network before being forwarded to the final destination. However, this approach is less
efficient than Mobile IPv6. GRE – Generic Routing Encapsulation.
- IPv6 has 6 types of extension headers. When multiple extension headers are used in the same
packet, the order of the extension header as specified in RFC 1883 is as below:
Note: The source node must follow this order; while the destination node may receive in any order