Information Technology Reference
In-Depth Information
32 bytes Source and destination IPv6 addresses
8 bytes Version field, traffic class field, flow label field, payload length field, next
header field, and hop limit field
You don't have to waste your time with a checksum validation anymore, and you don't have
to include the length of the IP header (it's fixed in IPv6; the IP header is variable length in
IPv4, so the length must be included as a field).
IPv6 Mobility IPv6 is only a replacement of the OSI layer 3 component, so you'll continue
to use the TCP (and UDP) components as they currently exist. IPv6 addresses a TCP issue,
though. Specifically, TCP is connection oriented, meaning that you establish an end-to-end
communication path with sequencing and acknowledgments before you ever send any data,
and then you have to acknowledge all of the pieces of data sent. You do this through a
combination of an IP address, port number, and port type (socket).
If the source IP address changes, the TCP connection may be disrupted. But then how
often does this happen? Well, it happens more and more often because more people are
walking around with a wireless laptop or a wireless Voice over IP (VoIP) telephone. IPv6
mobility establishes a TCP connection with a home address and, when changing networks,
it continues to communicate with the original endpoint from a care-of address as it changes
LANs, which sends all traffic back through the home address. The handing off of network
addresses does not disrupt the TCP connection state (the original TCP port number and
address remain intact).
Improved Security Unlike IPv4, IPv6 has security built in. Internet Protocol Security (IPsec)
is a component used today to authenticate and encrypt secure tunnels from a source to a
destination. This can be from the client to the server or between gateways. IPv4 lets you
do this by enhancing IP header functionality (basically adding a second IP header while
encrypting everything behind it). In IPv6, you add this as standard functionality by using
extension headers. Extension headers are inserted into the packet only if they are needed.
Each header has a “next header” field, which identifies the next piece of information. The
extension headers currently identified for IPv6 are Hop-By-Hop Options, Routing, Fragment,
Destination Options, Authentication, and Encapsulating Security Payload. The Authentication
header and the Encapsulating Security Payload header are the IPsec-specific control headers.
IPv4 to IPv6 Interoperability
Several mechanisms in IPv6 make the IPv4-to-IPv6
transition easy.
A simple dual-stack implementation where both IPv4 and IPv6 are installed and
used is certainly an option. In most situations (so far), this doesn't work so well
because most of us aren't connected to an IPv6 network and our Internet connec-
tion is not IPv6 even if we're using IPv6 internally. Therefore, Microsoft includes
other mechanisms that can be used in several different circumstances.
Intra-Site Automatic Tunnel Addressing Protocol (ISATAP) is an automatic tun-
neling mechanism used to connect an IPv6 network to an IPv4 address space (not
using NAT). ISATAP treats the IPv4 space as one big logical link connection space.
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