Frequently asked questions - Version 2.0


MTU (Maximum Transmission Unit)

An MTU (maximum transmission unit) is the largest size packet or frame that can be sent over a packet- or frame-based network (such as a network using TCP/IP). The MTU is expressed as an octet, a unit of eight-bit bytes. The MTU is used by the TCP (Transmission Control Protocol) to determine the size of each packet in a given transmission. If the MTU size is too great, re-transmissions may be required when a packet is processed by a router that can't handle such large packets. When the MTU is too small, relatively more header overhead and more acknowledgements must be sent and handled.

Receive Window

Specifies the default Receive Window size published by TCP. The TCP Receive Window size refers to the amount of Receive Data (in bytes) that can be buffered at one time on a connection. The host transmitting can send only that amount of data before it requires an acknowledgment and window update from the receiving host. In general, larger receive windows that can accommodate Receive Data will show better performance over high (delay * bandwidth ) networks. A Receive Window value that is an even multiple of the TCP Maximum Segment Size (MSS) will be most efficient The MSS value equals the MTU value minus 40.

Time To Live

This sets the default TTL or Time-to-Live value in the header of outgoing IP packets. The TTL specifies the period of time an IP packet that has not been delivered to its destination can remain on the network before being deleted.

Session Keep Alive

This value tells the system how often to send session keep alive packets on active sessions. This will keep connections that have stalled during a particular download session from timing out.

Note: This value should not be changed under Windows 95 or Windows 98.

MTU Auto Discovery

Determines whether TCP/IP will use a specified default Maximum Transmission Unit or automatically attempt to carry out MTU discovery over a path to a remote host.

MTU Black Hole Detect

Determines whether the stack will try to find Maximum Transmission Unit (MTU) routers that do not send back required ICMP fragmentation messages. (If this parameter is selected unnecessarily it can cause reduce system performance.)

Optimize Internet Explorer

Speeds up loading of web pages by increasing the number of simultaneous connections used by the Internet Explorer.

Extra Optimizations

Selective Acknowledgements:
SACK acknowledges receipt of individual data packets in a continuous sequence, as opposed to noting only the last sequence number. The sender can be notified by the recipient that one or more data blocks are missing from the middle of a sequence, and then only the missing data can be re-transmitted by the sender.

When TCP connections experience IP packet loss over the network, this allows Fast Retransmission and Fast Recovery. A TCP sender may quickly identify a single packet loss by reception of duplicate acknowledgements for a transmitted TCP/IP packet that was already acknowledged. This feature is effective in mitigating periodic congestion problems over a network. When 3 successive duplicate acknowledgements have been received the TCP sender determines that it can re-transmit the last unacknowledged TCP/IP packet (Fast Re-transmit) instead of beginning a TCP slow start due the loss of a single packet (Fast Recovery).

DNS Cache

What is DNS?

Domain Name System. The classification system by which domain names are identified, located and ultimately translated into website or web page addresses meeting Internet protocol standards allowing information to be sent between computers over the Internet. A domain name is usually an easily remembered or meaningful “nickname” for a combination of network addresses that uniquely identifies a given website.

How does DNS Cache work?

The DNS Cache functions as an archive of the translations of local domain names into IP addresses. The IP address is a usually a 32-bit number that identifies each sender or receiver of information that is sent in packets across the Internet. All requests for DNS translations go through the DNS Cache in order to reduce browsing overheads.

Available Options:

Enable DNS Cache
Enable or disable the DNS Cache. When the DNS Cache is disabled, all DNS requests are forwarded to the external server.
When disabling the DNS Cache, the user has an option to uninstall the DNS Cache.

Automatically add new domains
When this option is selected, new domain requests are automatically added to the DNS Cache along with their IP addresses.

When this option is selected, the specified time determines how often a new domain added to the DNS Cache should be refreshed. Refreshing a domain means sending the DNS request to the external server.

Available Actions:

Import Favorites
Reads all records from the Favorites address list, retrieves their IP addresses and adds them to the DNS Cache database.

Manual Add
Add a new record to the DNS Cache by manually typing in the URL name and the IP (or IPs) associated with it. In addition to entering IP addresses, the user can supply an alias name for the specified URL, which will then be translated into the same IP addresses as the real domain name.

Exclude List
This list contains URL addresses (or wildcards) that are not to be searched for in the DNS Cache. You can view the list, add or delete items, or restore the original list.

View Servers
View the list of DNS servers that are used by the DNS Cache to translate URLs into IP addresses. You can add new servers, remove unwanted servers, or change the order in which the servers are listed. Note: This option is recommended for experienced users only.

Clear Database
Removes all domains from the DNS Cache.


Cache Hits
The percentage of DNS requests that was resolved using the local cache and not forwarded to the external server.

Domains Count
Shows the number of URLs currently saved in the DNS Cache.

Access Count
The number of DNS requests that were locally resolved through the cache, without sending the request outside.

Forward Count
The number of DNS requests that were forwarded to the external DNS server.
A request is forwarded if it is not in the DNS Cache, or when its expiration date is reached and it needs to be refreshed by being sent to the external server.