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10-69

IPv4 Access Control Lists (ACLs)

Configuring Extended ACLs

[established] — This option applies only where TCP is the

configured protocol type. It blocks the synchronizing packet

associated with establishing a TCP connection in one direction

on a VLAN while allowing all other IPv4 traffic for the same

type of connection in the opposite direction. For example, a

Telnet connect requires TCP traffic to move both ways between

a host and the target device. Simply applying a deny to inbound

Telnet traffic on a VLAN would prevent Telnet sessions in either

direction because responses to outbound requests would be

blocked. However, by using the established option, inbound

Telnet traffic arriving in response to outbound Telnet requests

would be permitted, but inbound Telnet traffic trying to estab-

lish a connection would be denied.

TCP Control Bits. In a given ACE for filtering TCP traffic

you can configure one or more of these options:

[ ack ] — Acknowledgement.

[ fin ] — Sender finished.

[ rst ] — Connection reset.

[ syn ] — TCP control bit: sequence number synchronize.

For more on using TCP control bits, refer to RFC 793.

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HP E3800 Series Specifications

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