Windows NT and UDP checksums

I kept this in my mailbox for adding to the DNS-WG minutes whenever
they came out.  Since it appears they will not, I'll just send it to
the list...


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Date:     Sun, 28 Apr 96 15:35:17 MET DST
From:     Peter Lothberg <roll at Stupi.SE>
To:       staff at ripe.net
Subject:  Windows NT and UDP checksums


It was discussed at the ripe meeting, if NT could support UDP checksums or not,
it turns out that it can...

- --Peter

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REG: TCP/IP Transport Entries, PART 1
Article ID: Q102973
Revision Date: 05-APR-1996

The information in this article applies to:

 - Windows NT operating system version 3.1
 - Windows NT Advanced Server version 3.1


The article contains REGISTRY entries for the TCP/IP Transport Entries, Part 
1. These subgroups are included:

 - TCP/IP Parameters Subkey Entries
 - Adapter Card Parameters for TCP/IP


This is the first of two articles on these entries; for the other entries, 
see "TCP/IP Transport Entries, Part 2."

TCP/IP TRANSPORT ENTRIES

The various TCP/IP keys do not appear in the Registry unless TCP/IP is 
installed using the Network icon in Control Panel.

With Registry Editor, you can modify the following parameters for the TCP/IP 
transport. This section does not include all the TCP/IP
parameters that can be set using the Networks application in Control Panel.

The startup parameters defined in this section are found in these subkeys of
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services:

   TCPIP\Parameters
   adapter_name#\Parameters\TCPIP, (where adapter_name# indicates a
                      Services subkey for a network adapter
                      card)
   Ftpsvc\Parameters
   NBT\Parameters
   Streams\Parameters


Parameters for network bindings for this service are described in the 
article "NetRules Subkey Entries." See also
IsDomainMasterBrowser in the article "Browser Service Entries."

TCP/IP PARAMETERS SUBKEY ENTRIES

The entries for TCP/IP parameters appear under the following Registry path:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters


ArpCacheLife REG_DWORD Number of Seconds

Default: 600  (10 minutes)


Determines the default lifetime for entries in the ARP cache table. Once an 
entry is placed in the ARP cache, it is allowed to remain
there until its lifetime expires or until its table entry is reused because 
it is the oldest entry.

ArpCacheSize REG_DWORD Number Default: 62

Determines the maximum number of entries that the ARP cache table can hold. 
The ARP cache is allowed to grow dynamically until
this size is reached. After the table reaches this size, new entries can 
only be added by replacing the oldest entries that exist.

DatabasePath REG_EXPAND_SZ Pathname Default: 
%SystemRoot%\system32\drivers\etc

Determines where TCP/IP and NBT look for the hosts, services, networks, 
protocols, NETRC, and LMHOSTS files.

IpEnableRouter REG_DWORD 0 or 1 Default: 0 (false)

Determines whether IP routing is enabled between local interfaces. IP 
routing is always enabled for packets generated by the local
host. This parameter determines whether, for packets received on an 
interface and not destined for this host, IP will attempt to actively
forward the packets to hosts that can be reached via its other interfaces.

IpReassemblyTimeout REG_DWORD Number of seconds Default: 60 seconds

Determines how long IP accepts fragments when attempting to reassemble a 
previously fragmented packet. That is, if a packet is
fragmented, all of the fragments must make it to the destination within this 
time limit; otherwise, the fragments will be discarded and
the packet will be lost.

TcpDisableReceiveChecksum REG_DWORD 0 or 1 Default: 0 (false, that is, 
checksums will be checked on receives)

Specifies whether Checksums is disabled on receive.


TcpDisableSendChecksum REG_DWORD 0 or 1

Default: 0 (false, that is, checksums will be generated on sends)

Specifies whether Checksums is disabled on send.


TcpKeepCnt REG_DWORD Number in Minutes

Default: 120


Specifies how often TCP/IP will generate keep-alive traffic. When TCP/IP 
determines that no activity has occurred on the connection
within the specified time, it generates keep-alive traffic to probe the 
connection. After trying TcpKeepTries number of times to deliver
the keep-alive traffic without success, it marks the connection as down.

TcpKeepTries REG_DWORD Number Default: 20

Specifies the maximum number of times that TCP/IP will attempt to deliver 
keep-alive traffic before marking a connection as down.

TcpLogLevel REG_DWORD Number Default: 16 (log everything)

Specifies how verbose TCP/IP should be about logging events in the event 
log. The highest level of verbosity is 16, and 1 is the
lowest level. The following shows general information about these levels.

   Level   Events to be included
   ---------------------------------------------
   1     Only the most critical errors
   4     Serious protocol violations
   8     Nonserious protocol violations
   12    Information about unusual events
   16    Information about unusual events that
       some networks normally allow


TcpMaxConnectAttempts REG_DWORD Number

Default: 3


Specifies the maximum number of times TCP/IP attempts to establish a 
connection before reporting failure. The initial delay between
connection attempts is 3 seconds. This delay is doubled after each attempt.

TcpMaxRetransmissionAttempts REG_DWORD Number Default: 7

Specifies the maximum number of times that TCP/IP attempts to retransmit a 
piece of data on an established connection before ending
the connection. The initial delay before retransmitting is based on the 
current estimate TCP/IP makes of the round-trip time on the
connection. This delay is doubled after each retransmission. Acknowledgment 
of the data results in a recalculation of the estimate for
the round-trip time.

TcpNumConnections REG_DWORD Number Default: 64

Specifies the maximum number of TCP endpoints.


TcpRecvSegmentSize REG_DWORD Bytes

Default: 1460


Specifies the maximum receive segment size.


TcpSendDownMax REG_DWORD Number

Default: 16384


Specifies the maximum number of bytes queued by TCP/IP.


TcpSendSegmentSize REG_DWORD Bytes

Default: 1460


Specifies the maximum send segment size.


TcpWindowSize REG_DWORD Number

Default: 8192


Sets the size of the TCP send and receive windows, which is the amount of 
data that can be accepted in a single transaction. This
parameter is important in transferring files between a client and a server 
and is critical for performance for one-way traffic, such as for
FTP.

UdpDisableReceiveChecksum REG_DWORD 0 or 1 Default: 0 (false--that is, 
checksums will be checked on receives)

Specifies whether Checksums is disabled on receive.


UdpDisableSendChecksum REG_DWORD 0 or 1

Default: 0 (false--that is, checksums will be generated on sends)

Specifies whether Checksums is disabled on send.


UdpNumConnections REG_DWORD Number

Default: 64


Specifies the maximum number of UDP endpoints.


ADAPTER CARD PARAMETERS FOR TCP/IP

These parameters for TCP/IP are specific to individual network adapter 
cards. These appear under the following Registry path, where
adapter name# refers to the Services subkey for the specific adapter card:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
      \adapter name#\Parameters\Tcpip


BroadcastType REG_DWORD 0 or 1

Default: 1 (all 1 s)


Determines whether broadcast packets contain all 0 s or all 1 s as the 
broadcast address. The most common broadcast type is all 1 s.
The all-0 s setting is provided for compatibility with BSD 4.2 systems.

ForwardBroadcasts REG_DWORD 0 or 1 Default: 0 (false)

Specifies whether broadcasts should be forwarded between adapters. If 
enabled, broadcasts seen by this interface are forwarded to
other IP interfaces.

KeepAlive REG_DWORD 0 or 1 Default: 1 (true)

Determines whether TCP connections that request keep-alive packets result in 
keep-alive packets being sent. This feature is used to
determine when inactive connections can be disconnected. When a connection 
becomes inactive, keep-alive packets are periodically
exchanged. When 20 (the default value for TCPKeepTries) consecutive 
keep-alive packets go unanswered, the connection is broken.
This disconnect is initiated by the endpoint that is sending keep-alive 
packets.

MTU REG_DWORD Number in octets Default: 0 (That is, use the value supplied 
by the adapter.)

Specifies the maximum transmission unit size of an interface. Each interface 
used by TCP/IP may have a different MTU value specified.
The MTU is usually determined through negotiation with the lower driver, 
using that lower driver s value. However, that value may be
overridden.

Ideally, the MTU should be large enough to hold any datagram in one frame. 
The limiting factor is usually the technology making the
transfer. Some technologies limit the maximum size to as little as 128; 
Ethernet limits transfers to 1500; and proNet-10 allows as many as
2044 octets per frame.

Datagrams larger than the MTU value are automatically divided into smaller 
pieces called fragments; size is a multiple of eight octets.
Fragmentation usually occurs somewhere through which the traffic must pass 
whose MTU is smaller than the encapsulated datagram.
If fragmentation occurs, the fragments travel separately to the destination 
computer, where they are automatically reassembled before
the datagram is processed.

RouterMTU REG_DWORD Number in octets Default: 0 (That is, use the value 
supplied by the lower interface.)

Specifies the maximum transmission unit size that should be used when the 
destination IP address is on a different subnet. Each
interface used by TCP/IP may have a different RouterMTU value specified. In 
many implementations, the value of RouterMTU is set
to 576 octets. This is the minimum size that must be supported by any IP 
node. Because modern routers can usually handle MTUs
larger than 576 octets, the default value for this parameter is the same 
value as that used by MTU.

Trailers REG_DWORD 0 or 1 Default: 0 (false)

Specifies whether the trailer format is used. This feature provides 
compatibility with BSD 4.2 systems. When this feature is enabled,
TCP/IP header information follows the data area of IP packets.

Reference: "The Windows NT Resource Kit for Operating System Version 3.1"

Additional reference words: prodnt 3.10



KBCategory: kbother
KBSubcategory: ntregistry

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