3Com CoreBuilder 3500, Implementation Manual, Page: 494 / 592

494 C
HAPTER
17: Q
O
S
AND
RSVP
Specifying TCP Drop
Control
The TCP drop control option lets you create a control for packets used to
establish TCP connections. This control affects QoS Flow Classifiers that
have TCP traffic going from “source” IP addresses to “destination” IP
addresses.
TCP drop control does not function with nonflow classifiers or UDP. It is
only available for flow classifiers that include TCP.
Figure 83 illustrates how TCP handshaking works between the source
and destination to establish a connection. By dropping only the
initial TCP
packet used to establish TCP connections (those packets containing a
signature of SYN=1, ACK=0), you can establish one-way TCP flow
filtering.
Figure 83 3-way TCP Handshake
Figure 84 shows an example with TCP drop control disabled.
Figure 84
QoS Control Action (Drop Control Disabled)
With the QoS Classifier and QoS Control definition shown in Figure 84
(TCP control is not enabled), any attempt by a client on the End-user
network to establish a TCP connection to a server on the Admin network
fails.
SYN=1, ACK=0
SYN=1, ACK=1
SYN=0, ACK=1
Destination
Source
QoS Classifier:
Source IP:
0.0.0.0
Destination IP:
10.1.1.0
QoS Control Action:
Drop all
10.1.1.254 10.1.2.254
Admin
End-user
network