D-Link DFL-260E User Manual page 516

13.2. TCP Level Settings
Chapter 13. Advanced Settings
TCP Auto Clamping
Automatically clamp TCP MSS according to MTU of involved interfaces, in addition to
TCPMSSMax.
Default: Enabled
TCP Zero Unused ACK
Determines whether NetDefendOS should set the ACK sequence number field in TCP packets to
zero if it is not used. Some operating systems reveal sequence number information this way, which
can make it easier for intruders wanting to hijack established connections.
Default: Enabled
TCP Zero Unused URG
Strips the URG pointers from all packets.
Default: Enabled
TCP Option WSOPT
Determines how NetDefendOS will handle window-scaling options. These are used to increase the
size of the window used by TCP; that is to say, the amount of information that can be sent before the
sender expects ACK. They are also used by OS Fingerprinting. WSOPT is a common occurrence in
modern networks.
Default: ValidateLogBad
TCP Option SACK
Determines how NetDefendOS will handle selective acknowledgement options. These options are
used to ACK individual packets instead of entire series, which can increase the performance of
connections experiencing extensive packet loss. They are also used by OS Fingerprinting. SACK is
a common occurrence in modern networks.
Default: ValidateLogBad
TCP Option TSOPT
Determines how NetDefendOS will handle time stamp options. As stipulated by the PAWS (Protect
Against Wrapped Sequence numbers) method, TSOPT is used to prevent the sequence numbers (a
32-bit figure) from "exceeding" their upper limit without the recipient being aware of it.
This is not normally a problem. Using TSOPT, some TCP stacks optimize their connection by
measuring the time it takes for a packet to travel to and from its destination. This information can
then be used to generate resends faster than is usually the case. It is also used by OS Fingerprinting.
TSOPT is a common occurrence in modern networks.
Default: ValidateLogBad
TCP Option ALTCHKREQ
Determines how NetDefendOS will handle alternate checksum request options. These options were
516