Net Boost 2004

- Eric J. Klein (Windows 98, Microsoft Internet Explorer 5.0 User, USA)

- Caroline E. Petitjean (Windows 98, Microsoft Internet Explorer 5.0 User, Netherlands)

- Aaron M. Sloman (Windows 98, AOL User, USA)

Download NetBoost 2005

MaxMTU
MTU is the Maximum Transmission Unit that IP is allowed to use for a particular interface. In general, the bigger the packet, the more data is transferred in the same number of packets, so the routers work better and you experience higher throughput. If your MTU is set too big however, your packets must be fragmented, or broken up, by a router along the path to the server. This results in a drastic decrease in throughput because the destination has to reassemble the packets that the routers took the trouble to fragment along the way and this thread of the code in both server and router is usually sub-optimal. Therefore, you want to set the MTU for each individual interface as big as possible but not so big as to cause fragmentation along your most common paths. In practice, this is not as difficult as it sounds. While it is true that MTU can vary along every path your data follows to its various destinations, in practice the Internet has only two or three MTU settings and the proper MTU setting for your network adapters is easily determined with some simple tests. Most of the Internet is built on Ethernet and serial lines. Ethernet has a maximum frame payload of 1500 bytes, so the biggest MTU that you can possibly use on an Ethernet is 1500 bytes, no matter what the MTU size is anywhere else on the Internet. Win9x uses a default value of 1500 for Ethernet adapters. The high-speed serial lines that make up the backbone of the Internet have MTUs that match or exceed the MTU of Ethernet. High-speed local-access circuits like cable modems, DSL, frame relay, T-1, and T-3 circuits have MTUs that match or surpass the Ethernet MTU. In these situations the Microsoft default value of MTU=1500 bytes works best. Unfortunately, the low speed serial lines that connect dial-up telephone lines and ISDN to the Internet do not always use the Ethernet MTU size. Those access servers that don't support Ethernet frame sizes use the minimum allowable MTU setting of 576 bytes or an intermediate frame size of about 1000 bytes. If your network gateway dial-up adapter is used to connect to the Internet via dial-up analog modem or ISDN, you should test the MTU to see whether you can use the 1500 byte default, the intermediate setting of 1000 bytes, or the minimum 576 byte setting. Microsoft defaults to a MTU (MaxMTU) of 1500 on all interfaces for Win95 DUN 1.2 and earlier. DUN 1.3 and Win98 add a configuration parameter for MTU (IPMTU) to the Dial-Up Adapter with a default of "AUTO" which sets MTU=576 for speeds of 128 kbps or less and MTU=1500 for higher speeds. In addition to the AUTO setting, you may select "Small" for MTU=576, "Medium" for MTU=1000, and "Large" for MTU=1500 and override the AUTO setting. 

RWIN (TCP Recieve Window)
The TCP Receive Window size is the amount of receive data (in bytes) that can be buffered at one time on a connection. The sending host can send only that amount of data before waiting for an acknowledgment and window update from the receiving host. Matching the receive window to even increments of the MSS increases the percentage of full-sized TCP segments utilized during bulk data transmission. MSS is the MaxMTU - 40 bytes for TCP and IP headers. The RWIN default is 8192 bytes rounded up to the nearest MSS increment for the connection. If that isn't at least 4 times the MSS, then it's adjusted to 4 * MSS, with a maximum size of 64K. With the Windows 95 default MaxMTU of 1500, the default RWIN is rounded up to 8760 (1460 * 6). You can greatly improve performance by setting this to a lower value such as 4 times your MSS (MTU-40). The idea is to bring it to a value below 8192. Many people have better success with 6, 8 or even 10* MSS. In some cases, however, manually setting RWIN may decrease performance because it takes the control away from windows, and if the MTU is negotiated to a different value, then the size of the RWIN is no longer an whole integer multiple. For this to be effective you must make sure your MTU is set where it will not be negotiated to a lower value

TTL (Time To Live)
TTL is a field in the IP header which indicates how long a packet should be allowed to survive before it is discarded. TTL essentially determines the maximum number of hops permitted. Windows 95 default is 32, but with the Internet growing larger all the time, it is worth changing it to the larger setting of 64. 

Auto Discovery
Auto Detection is Enabled by Default. This option enables the system to automatically determine the Maximum Transmission Unit (MTU) value and detect routers which do not return appropriate ICMP messages under some conditions. Enabling this setting causes TCP to attempt to discover the Maximum Transmission Unit (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 is supposed to be able to eliminate fragmentation at routers along the path that connect networks with different MTUs. This requires implementation of the corresponding server side algorithm, however, and presupposes all of the servers on the entire Internet only running MSFT server software with server-side optimization features accessible from MSFT web-browser client software. However, it is not recommended to disable this setting as it would then cause an MTU of 576 bytes to be used for all connections that are not to machines on the local subnet. Disabling this setting can cause severe performance degradation because fragmentation may not be compensated for. 

Black Hole Detection
Black Hole Detection is Disabled by default. Enabling this option forces the system to try to detect black hole routers. Black hole routers are routers that do not send back ICMP (Internet Control Message Protocol) fragmentation-needed messages while automatically determining the optimal MTU value. This increases the maximum number of retransmissions performed for a given segment. Setting this parameter when it is not needed can cause performance degradation. So it is not recommended that you enable this option unless you understand the implications of doing so.