52
Enhancements
Release M.10.02 Enhancements
Figure 4. The Packet-Filtering Process in an ACL with
N
Entries (ACEs)
N o t e
The order in which an ACE occurs in an ACL is significant. For example, if an ACL contains six ACEs,
but the first ACE is a “permit IP any”, then the ACL permits all IP traffic from the authenticated client,
and the remaining ACEs in the list do not apply, even if they specify criteria that would make a match
with any of the traffic permitted by the first ACE.
Is there a
match?
Perform action
(permit or deny).
No
Test 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.
