Page 9 | AlliedWare™ OS How To Note: Hardware Filters
How many filters can you create?
The following figure shows the copies of these rules.
When a QoS policy has been applied to ports 4 and 5, all the hardware filter rules have to be
replicated further down in the rule table, and the QoS-specific rules added to the table below
this copy of the hardware filter rules. For ports 4 and 5, the rule comparison process starts
at entry 9 in the rule table, not at entry
1
.
The entries 5-8 in the table have been left blank because separate sets of rules in the rule
table must begin at an 8-entry boundary.
So, if there are several QoS policies configured on the switch, then there will be several
copies of the hardware filter rules within the rule table. This, of course, can significantly
reduce the maximum number of hardware filters that can be created.
Also, the protocols that use filters (see
page 11
) create at least one entry each.
2. The profile (mask)
The other item that affects the number of filters you can create is called the profile.
Conceptually, this is a
1
6-byte mask that decides which set of bytes should be extracted from
a packet as it enters the filtering process, to be compared against all the hardware filter and
QoS classifiers. Hardware filters and QoS share a single mask.
In effect, the mask is the sum of all the individual bytes required for each individual classifier
parameter. The number of bytes required by each classifier parameter depends on what fields
it maps on. For example:
source MAC address—6 bytes
destination MAC address—6 bytes
Port
Start
1
Rule
1
1
1
2
Rule 2
2
1
3
Rule 3
3
1
4
Rule 4
4
9
5
5
9
6
6
1
7
...
...
8
...
...
9
Copy of rule
1
1
0
Copy of rule 2
11
Copy of rule 3
1
2
Copy of rule 4
1
3
QoS rule #
1
52
1
1
4
QoS rule #2
Table that maps ingress port
to the starting point of the
rule comparison process
Rule table
