LevelOne GTL-2691 - Manual (Page 351)

C HAPTER 13 | Security Measures
Access Control Lists
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A CCESS C ONTROL L ISTS
Access Control Lists (ACL) provide packet filtering for IPv4 frames (based
on address, protocol, Layer 4 protocol port number or TCP control code),
IPv6 frames (based on address, next header type, or flow label), or any
frames (based on MAC address or Ethernet type). To filter incoming
packets, first create an access list, add the required rules, and then bind
the list to a specific port.
Configuring Access Control Lists –
An ACL is a sequential list of permit or deny conditions that apply to IP
addresses, MAC addresses, or other more specific criteria. This switch tests
ingress packets against the conditions in an ACL one by one. A packet will
be accepted as soon as it matches a permit rule, or dropped as soon as it
matches a deny rule. If no rules match, the packet is accepted.
C OMMAND U SAGE
The following restrictions apply to ACLs:
◆ The maximum number of ACLs is 32.
◆ The maximum number of rules per ACL is 96.
◆ The maximum number of rules that can be bound to the ports is 96 for
each of the following list types: MAC ACLs, IP ACLs (including Standard
and Extended ACLs), IPv6 Standard ACLs, and IPv6 Extended ACLs.
The maximum number of rules (Access Control Entries, or ACEs) stated
above is the worst case scenario. In practice, the switch compresses
the ACEs in TCAM (a hardware table used to store ACEs), but the actual
maximum number of ACEs possible depends on too many factors to be
precisely determined. It depends on the amount of hardware resources
reserved at runtime for this purpose.
Auto ACE Compression is a software feature used to compress all the
ACEs of an ACL to utilize hardware resources more efficiency. Without
compression, one ACE would occupy a fixed number of entries in TCAM.
So if one ACL includes 25 ACEs, the ACL would need (25 * n) entries in
TCAM, where “n” is the fixed number of TCAM entries needed for one
ACE. When compression is employed, before writing the ACE into
TCAM, the software compresses the ACEs to reduce the number of
required TCAM entries. For example, one ACL may include 128 ACEs
which classify a continuous IP address range like 192.168.1.0~255. If
compression is disabled, the ACL would occupy (128*n) entries of
TCAM, using up nearly all of the hardware resources. When using
compression, the 128 ACEs are compressed into one ACE classifying
the IP address as 192.168.1.0/24, which requires only “n” entries in
TCAM. The above example is an ideal case for compression. The worst
case would be if no any ACE can be compressed, in which case the used
number of TCAM entries would be the same as without compression. It
would also require more time to process the ACEs.