How many filters can you create?

The total number of filters that can be created is not an exact number, but depends on which fields the various filters are matching on. So, to understand how to work out whether the set of filters you are creating might run out of space, it is necessary to understand the way in which the filters operate in the switch hardware.

There are two items within the switch hardware which set limits on the number of filters that can be created: the filter rules table and the profile (mask).

Filters share the same filter rules table and mask whether they are made by applying ACLs directly to ports or are made through QoS class-maps.

1. The filter rules table

One item that sets a limit on the number of filters is the table that contains the list of filter rules. This has a strict limit of 1024 entries. An entry gets made when:

zYou apply an ACL to a port (with the ip access-groupor mac access-groupcommand)

zYou apply a QoS class-map to a port by applying its policy-map to a port (with the service- policy input command). For each class-map, its ACL and any match commands are ANDed together to make a single filter entry.

Therefore, every ACL or class-map uses up one table entry for every port that it is applied to. Interface ACL rules come before QoS class-map rules. Conceptually, the table looks like:

port1.0.1	Interface ACL rule
	Interface ACL rule
	...
	QoS class-map rule
	QoS class-map rule
	...

port1.0.2	Interface ACL rule
	Interface ACL rule
	...
	QoS class-map rule
	QoS class-map rule
	...

...	...

If you specify a TCP or UDP port range, this may use multiple filter entries. The switch converts the range to a series of single TCP/UDP port numbers plus masks. It uses as few entries as possible to cover the range.

Also, the protocols that use filters (CPU protection and EPSR—see page 21) create one entry per port.

Page 18 AlliedWare Plus™ OS How To Note

X900-12XT/S, x908 specifications

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Allied Telesis x908, X900-12XT/S manual How many filters can you create?, Filter rules table

Models: X900-12XT/S x908

1. The filter rules table

X900-12XT/S, x908 specifications