Nortel Networks WEB OS 212777 - Manual (Page 197)

Web OS 10.0 Application Guide
Chapter 7: Filtering n 197
212777-A, February 2002
Matching TCP Flags
Web OS supports packet filtering based on any of the following TCP flags.
Any filter may be set to match against more than one TCP flag at the same time. If there is
more than one flag enabled, the flags are applied with a logical AND operator. For example, by
setting the switch to filter
SYN and ACK , the switch filters all SYN-ACK frames.
N OTE – TCP flag filters must be cache-disabled. Exercise caution when applying cache-
enabled and cache-disabled filters to the same switch port. For more information, see “Cache-
Enabled versus Cache-Disabled Filters” on page 178 .
Configuring the TCP Flag Filter
N OTE – By default, all TCP filter options are disabled. TCP flags will not be inspected unless
one or more TCP options are enabled.
Consider the following network:
Figure 7-11 TCP ACK Matching Network
Table 7-5 TCP Flags
Flag Description
URG Urgent
ACK Acknowledgement
PSH Push
RST Reset
SYN Synchronize
FIN Finish
SMTP
Mail Server
Router
Web Switch
Web Servers:
203.122.186.*
Internet
Inside/
Trusted LAN
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