Learning About The Dual Stack And The Ip Management Enhancements - Microsoft Windows Vista Manual

To optimize throughput in high-loss environments, the Next Generation TCP/IP stack sup-
ports industry standard Requests For Comments (RFCs) 2582, 2883, 3517, and 4138. These
changes allow the Next Generation TCP/IP stack to:
Modify how the TCP fast recovery algorithm is used. The new algorithm provides faster
throughput by changing the way that a sender can increase its sending rate when multi-
ple segments in a window of data are lost and the sender receives an acknowledgement
stating that only part of the data has been successfully received. The old algorithm
worked well for single lost segments, but it did not perform well when multiple lost
segments were involved.
Extend the use of the Selective Acknowledgement (SACK) option for TCP. This option
now allows a receiver to indicate up to four noncontiguous blocks of received data
and to acknowledge duplicate packets. The sender can then determine when it has
retransmitted a segment unnecessarily and adjust its behavior to prevent future
retransmissions.
Introduce a conservative SACK-based loss recovery algorithm for TCP. This new algo-
rithm makes it possible to use SACK information to perform loss recovery when TCP
senders receive duplicate acknowledgements and to recover more effectively and
quickly when multiple segments are not received at the destination.
Detect spurious retransmission time-outs (RTOs) with TCP. This provides correction for
sudden, temporary increases in RTOs and prevents unnecessary retransmission of
segments.

Learning About the Dual Stack and the IP Management Enhancements

As mentioned earlier, computers running Windows Vista have both IPv4 and IPv6 configured
by default. This is a major change from earlier versions of Microsoft Windows, in which only
IPv4 is used by default.
Windows Vista supports IPv4 and IPv6 by using the dual-layer Next Generation TCP/IP stack.
This stack features an implementation of IP in which IPv4 and IPv6 share common transport
and framing layers. Because Windows Vista enables IPv4 and IPv6 by default, there is no need
to install a separate component to obtain IPv6 support.
To make IPv6 more dynamic, Windows Vista includes a number of enhancements. These
enhancements include support for:
Symmetric network address translators (NATs)
(private) address and port number to different external (public) addresses and ports,
depending on the external destination address. This new behavior allows an IPv6 fea-
ture called Teredo to act as the go-between for a larger set of Internet-connected host
computers.
Chapter 12: Networking Your Computer
A symmetric NAT maps the internal
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