HP 6400cl, Management Manual, Page: 360 / 664

Access Control Lists (ACLs) for the Series 5300xl Switches
ACL Operation
N o t e o n I m p l i c i t
For ACLs configured to filter inbound packets on a VLAN, remember that
D e n y
Implicit Deny filters routed packets and any bridged packets with a DA
specifying the switch itself . This operation helps to prevent management
access from unauthorized IP sources.
Is there a
match?
Perform action
(permit or deny).
No
Test a packet against
criteria in first ACE.
Yes
No
Yes
Deny the packet
(invoke implicit
deny any ).
End
Perform action
(permit or deny).
End
End
Test the packet against
criteria in second ACE.
Is there a
match?
Test packet against
criteria in
N
th ACE.
Is there a
match?
No
Yes
End
Perform action
(permit or deny).
1. If a match is not found with
the first ACE in an ACL, the
switch proceeds to the next
ACE and so on.
2. If a match with an explicit
ACE is subsequently found,
the packet is either permit­
ted (forwarded) or denied
(dropped), depending on
the action specified in the
matching ACE. In this case
the switch ignores all sub-
sequent ACEs in the ACL.
3. If a match is not found with
any explicit ACE in the ACL,
the switch invokes the
implicit
deny IP any at the
end of every ACL, and
drops the packet.
Note: If the list includes a
permit IP any entry, no
packets can reach the
implicit
deny IP any at the
end of the list. Also, a
permit IP any ACE at any
point in an ACL defeats the
purpose of any subsequent
ACEs in the list.
Figure 9-3. The Packet-Filtering Process in an ACL with
N
Entries (ACEs)
9-14