Optional configurations for TCP/IP

[nullCRC]

Normally NOT found in the registry, but you can add them. Remember to back up your registry. I am not liable for anything done with this information.

1. KEY_LOCAL_MACHINE\\SYSTEM\CurrentControlSet\Servic es
2. Add a value to the key as described in the appropriate entry below by clicking Add Value on the Edit menu, and then setting the value type under Data Type.
3. Reboot

Parameters are located under one of two subkeys of
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es
Tcpip\Parameters
Tcpip\Parameters\Interfaces\ ID for Adapter

Where ID for Adapter represents the network adapter that TCP/IP is bound to. The relationship between an Adapter ID and Network Connection can be determined by examining HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\Network\{4D36E972-E325-11CE-BFC1-08002BE10318}\ ID for Adapter \Connection. The Name value provides the friendly name for a network connection used in Network Connections folder. Values under the latter keys are specific to each adapter.

ArpAlwaysSourceRoute
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False or True)
Default: 0 (False)
Description: Setting this parameter to 1 forces TCP/IP to transmit ARP queries with source routing enabled on Token Ring networks. The stack transmits ARP queries w/o source routing first and retries with source routing enabled if no reply was received.

ArpUseEtherSNAP
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False or True)
Default: 0 (False)
Description: Setting to 1 forces TCP/IP to transmit Ethernet packets using 802.3 SNAP encoding. By default, the stack transmits packets in DIX Ethernet format. Always receives both formats.

DefaultTTL
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number of
seconds/hops
Valid Range: 1-255
Default: 128 for Windows XP
Description: Sets default TTL value set in the header of outgoing IP packets. TTL determines the max. amount of time an IP packet can live in the network without reaching its destination. Limits on the number of routers an IP packet can pass through before being discarded.

EnableDeadGWDetect
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False, True)
Default: 1 (True)
Description: Setting to 1 causes TCP to perform Dead Gateway Detection. Enabled, TCP asks IP to change to a backup gateway if it retransmits a segment several times without receiving a response. Backup gateways may be defined Advanced section of TCP/IP configuration in Network Control Panel.

EnablePMTUBHDetect
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False, True)
Default: 0 (False)
Description: Set to 1 (True) causes TCP to try to detect Black Hole routers while doing Path MTU Discovery. Black hole routers do not return ICMP Destination Unreachable messages when it needs to fragment an IP datagram with the Don't Fragment bit set. TCP depends on receiving these messages to perform Path MTU Discovery. Enabled, TCP will try to send segments without the Don't Fragment bit set if several retransmissions of a segment go unacknowledged. If the segment is acknowledgedt, the MSS will be decreased and the Don't Fragment bit will be set in future packets on the connection. Enabling increases max. number of retransmissions for a segment.

EnablePMTUDiscovery
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False, True)
Default: 1 (True)
Description: Setting this to 1 (True) causes TCP to attempt to discover the MTU or largest packet size over the path to a remote host. By discovering the Path MTU and limiting TCP segments to this size, TCP can eliminate fragmentation along the path that connect networks with different MTUs. Fragmentation adversely affects TCP throughput and network congestion. Setting this parameter to 0 causes an MTU of 576 bytes to be used for all connections that are not to computers on the local subnet.

ForwardBufferMemory
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number of bytes
Valid Range: network MTU - some reasonable
value smaller than 0xFFFFFFFF
Default: 74240 (enough for fifty 1480-byte
packets, rounded to a multiple of 256)
Description: This parameter determines how much memory IP allocates to store packet data in the router packet queue. When this buffer space is filled, the router begins discarding packets at random from its queue. Packet queue data buffers are 256 bytes, so value should be multiple of 256. Multiple buffers are chained together for larger packets. IP header is stored separately. This is ignored and no buffers are allocated if the IP router is not enabled.

IGMPLevel
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number
Valid Range: 0,1,2
Default: 2
Description: Determines to what extent the system supports IP multicasting and participates in the Internet Group Management Protocol. At level 0, the system provides no multicast support. At level 1, the system can only send IP multicast packets. At level 2, the system can send IP multicast packets and participate in IGMP to receive multicast packets.

KeepAliveInterval
Key: Tcpip\Parameters
Value Type: REG_DWORD - Time in milliseconds
Valid Range: 1 - 0xFFFFFFFF
Default: 1000 (one second)
Description: Determines the interval separating keepalive retransmissions until a response is received. Once received, the delay until the next keepalive transmission is again controlled by the value of KeepAliveTime. Connection will be aborted after the number of retransmissions specified by TcpMaxDataRetransmissions have gone unanswered.

KeepAliveTime
Key: Tcpip\Parameters
Value Type: REG_DWORD - Time in milliseconds
Valid Range: 1 - 0xFFFFFFFF
Default: 7,200,000 (two hours)
Description: Controls how often TCP attempts to verify an idle connection is still intact. Not sent by default.

MTU
Key: Tcpip\Parameters\Interfaces\ ID for Adapter
Value Type: REG_DWORD Number
Valid Range: 68 - the MTU of the underlying network
Default: 0xFFFFFFFF
Description: Overrides default MTU for a nic. MTU is the max. packet size in bytes that will transmit over the network. This includes the transport header (IP datagrams can span multiple packets). Values larger than the default for the underlying network will result in using the network default MTU. Values smaller than 68 will result in the tranport's using an MTU of 68.

NumForwardPackets
Key: Tcpip\Parameters
Value Type: REG_DWORD Number
Valid Range: 1 - some reasonable value
smaller than 0xFFFFFFFF Default: 50
Description: Determines the number of IP packet headers allocated for the router packet queue. If all headers are in use, the router discards packets at random from the queue. Min. value should be as large as the ForwardBufferMemory value divided by the maximum IP data size of the networks connected to the router. Should be no larger than ForwardBufferMemory value divided by 256, since 256 bytes of forward buffer memory are used for each packet. The optimal number of forward packets for a given ForwardBufferMemory size depends on the type of traffic carried on the network and will be between these two values. Ignored and no headers are allocated if the router is not enabled.

TcpMaxConnectRetransmissions
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number
Valid Range: 0 - 0xFFFFFFFF
Default: 3
Description: This parameter determines the number of times that TCP retransmits a SYN before aborting. Retransmission timeout is doubled with each successive retransmission in a given attempt.

TcpMaxDataRetransmissions
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number
Valid Range: 0 - 0xFFFFFFFF
Default: 5
Description: Controls the number of times that TCP retransmits an individual data segment (non connect segment) before aborting. The retransmission timeout is doubled with each successive retransmission on a connection. Reset when responses resume. The base timeout value is dynamically determined by the measured round-trip time on the connection.

TcpNumConnections
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number
Valid Range: 0 - 0xfffffe
Default: 0xfffffe
Description: This parameter limits the maximum number of connections that TCP can have open simultaneously.

TcpTimedWaitDelay
Key: Tcpip\Parameters
Value Type: REG_DWORD - Time in seconds
Valid Range: 30-300 (decimal)
Default: 0xF0 (240 decimal)
Description: Determines time a connection stays in the TIME_WAIT state when being closed. During TIME_WAIT state, socket pair cannot be re- used. Known as the "2MSL" state, as by RFC the value should be twice the max. segment lifetime on the network.

TcpUseRFC1122UrgentPointer
Key: Tcpip\Parameters
Value Type: REG_DWORD - Boolean
Valid Range: 0,1 (False, True)
Default: 0 (False)
Description: Determines whether TCP uses the RFC 1122 specification for urgent data or the mode used by BSD- derived systems. The two mechanisms interpret the urgent pointer in the TCP header and the length of the urgent data differently. Not interoperable. Windows XP defaults to BSD mode.

TcpWindowSize
Key: Tcpip\Parameters
Value Type: REG_DWORD - Number of bytes
Valid Range: 0 - 0xFFFF
Default: The smaller of 0xFFFF OR (The larger of four times the max. TCP data size OR 8192 rounded up to an even multiple of the network TCP size.) The default is 8760 for Ethernet.
Description: Determines max. TCP receive window size offered. Receive window specifies # of bytes sender can transmit without receiving acknowledgment. Larger receive windows improve performance over high (delay * bandwidth) networks. For highest efficiency, the receive window should be an even multiple of the TCP MSS.

[Áedán]

Most of these settings aren't worth even bothering to think about playing with, unless you have a specific need, or you know a great deal about the way TCP/IP works.

Just thought I'd add a few words as to what the settings are useless for...There's only a handful of settings that are even worth looking at, much less tweeking.

ArpAlwaysSourceRoute
Unless you're on TokenRing, this does nothing at all. As I doubt anyone here uses TokenRing, it's not meaningful to people!

ArpUseEtherSNAP
Unless you've got some really wierd (old) TCP/IP hosts on your network, you won't need to tell Windows to use SNAP framing as opposed to Ethernet_II framing.

DefaultTTL
Win 95,98 and ME have a lower TTL than 2000. The TTL is basically how many routers your packet is allowed to pass through before being returned as unsendable. If you're going over 30 hops, consider that you might have routing problems somewhere!

EnableDeadGWDetect
This is only useful if you have multiple gateways that don't support HSRP or VRRP. I've never come across anyone who's needed this setting. For people on ISP connections, you'll only get one default gateway (and it might well be VRRP anyway.)

EnablePMTUBHDetect
Marginal at best. Basically tries to deal with routers that don't bother informing that there's a problem.

EnablePMTUDiscovery
Disabling this disables a critical part of TCP/IP - Path discovery. Basically disabling it, forces your MTU to 576 bytes, as all routers should be able to deal with 576 byte packets.

ForwardBufferMemory and NumForwardPackets
Sets the size of the buffer of memory used for routing packets when congestion occurs on a network interface. If you're not routing, this will take away memory from other processes. Most people won't be using 2000/XP for routing, instead using a router...


IGMPLevel
Allows you to turn off multicasting. Some streaming applications use multicasting. The benefit to turning it off? None basically.

KeepAliveInterval and KeepAliveTime
Used to keep an interactive session alive. Simply sends null packets to the far end to ensure the connection is kept up. This will only happen if the application specifies that the connection should be keepalive. Will consume bandwidth keeping the connection up.

MTU
Maximum transmission unit. Sets the largest packet size that can be TRANSMITTED. If you've got ethernet, setting this over 1432 makes no difference. If you suffer lost/corrupt packets, setting this smaller helps speed things up. If the path between you and the remote system only supports smaller MTUs, then the path discovery will ensure that your system only transmits packets as large as the weakest link can handle.

TcpMaxConnectRetransmissions
Sets how many times TCP will attempt to establish a connection before assuming the remote host isn't available. Setting this higher means that you can run over less reliable links, but timing out will take much longer. Increasing this by one doubles the timeout value. Increasing this by two doubles the doubled timeout. If you're on a reliable link this isn't of much benefit

TcpMaxDataRetransmissions
Sets how many times TCP will attempt to resend data on a connection before assuming the remote host isn't available. Like the above settings, increasing it by one doubles the timeout. Again, not much benefit on a reliable link.

TcpNumConnections
Sets how many open sockets TCP will support. Don't play unless you want to REDUCE the number of connections your machine can support.

TcpTimedWaitDelay
Changing this setting won't change your performance. It basically controls how long it takes for a socket to be closed. Tune it up if you find you are using more than 16,000 sockets every minute. Otherwise, leave well alone.

TcpUseRFC1122UrgentPointer
The Urgent pointer is a mechanism for sending an important packet out of sequence with the rest of the data. If you don't understand what Urgent packets are, and why there are two mutually excusive settings then don't play. Unlikely to make any difference unless you're using an application that requires Urgent packets.

TcpWindowSize
Sets how much data can be recieved before an ack is sent back to the sending machine. Setting it higher increases performance over links with latency, but increases the performance penalty should a packet go missing. Reducing it increases the speed at which the connection recovers if packets go missing, adversely affects performance. If you've got a high speed connection with little latency this will make less difference. If you've got a satellite connection, tune this upwards to help with the latency.



Phew! Hope that helps people understand why most of these settings aren't useful!
AidanII

[nullCRC]

I did'nt say they WERE worth bothering with, I just said they were normally not found in the registry but could be added.

Even if the resulting configuration resulted in a minor, minor increase, I would be happy knowing that I tweaked it (is tweek a eropean term? ).

[Áedán]

Yes, Europeans understand what "tweek" means - well at least the english speaking ones do.

Thing to remember is that TCP/IP was designed to be self tweeking for each connection, so there isn't a vast scope for improving it. There is plenty of scope for making things worse though!

The MSS (TcpWindowSize) is probably the only option worth looking at, and how you set that depends on the delay (latency) and bandwidth of your connection. Generally the MSS needs to be bigger if your (Delay * Bandwidth) is larger. That's why satellite connections often do well with a large MSS, as their delay is often over 200ms, but their bandwidth can be over 20Mbit/sec.

AidanII

[Pinky]

Adian, you continue to amaze me

concerning that last setting discussed, if my cable modem connection, because of poor routing and local node congestion, is almost twice as slow as it should be (in response times and not bandwidth), would increasing the TcpWindowSize aid in the sending of data when gaming or uploading (meaning, sending more at a time less of the time help?) ??

[Áedán]

Unfortunately, bringing the TCPWindowSize (MSS) up won't affect latency. It also won't affect uploading, as it's a receive window, rather than a transmit window. These things are negotiated, so it also depends on the machine at the other end of the link.

If you're seeing problems with lag with multiplayer games, which you already know are down to poor routing, then there's not a lot you can do, short of changing ISPs.

Sorry!

AidanII

[Pinky]

Originally posted by AidanII
Unfortunately, bringing the TCPWindowSize (MSS) up won't affect latency. It also won't affect uploading, as it's a receive window, rather than a transmit window. These things are negotiated, so it also depends on the machine at the other end of the link.

If you're seeing problems with lag with multiplayer games, which you already know are down to poor routing, then there's not a lot you can do, short of changing ISPs.

Sorry!

AidanII

Understood, thought I'd ask (nothing to lose really ). I like the download speeds and convenience just enough to stay with Roadrunner for now.

[Áedán]

Originally posted by Pinky
Adian, you continue to amaze me

What, that I'm a fount of useless knowledge?

AidanII

[mrpcman]

Originally posted by AidanII


What, that I'm a fount of useless knowledge?

AidanII

hey, well it's that useless knowledge that heps you understand everything else better.

[Dr_Romulus]

Originally posted by AidanII


What, that I'm a fount of useless knowledge?

AidanII

Thats a lot better than just being useless, isn't it??? :-D :-D