Rules engine for access control lists in network units

1. A rules engine for the examination of selected fields in an addressed data packet, comprising:

an access control list table containing entries each defining an access control list rule, a respective first action and a chain identifier; and

an extension rule table for entries each defining an extension rule, a respective second action and a respective rule identifier

wherein the rules engine is operative:

(a) to search said access control list table to ascertain a match between an access control list rule and said addressed data packet;

(b) to search said extension rule table to ascertain a match between an extension rule and said addressed data packet;

in the event of a matched access control list rule matched to said addressed data packet, to prescribe one of:

(ci) the respective second action associated with a matched extension rule in the event of correspondence between a chain identifier associated with the matched extension rule and a rule identifier identifying a match between that matched extension rule and said addressed data packet; or

(cii) in the absence of said correspondence, the respective first action associated with said matched access control list rule.

2. A rules engine as in claim 1 wherein said access control list rules relate to fields in TCP (Transmission Control Protocol) segments and network address fields.

3. A rules engine as in claim 1 wherein said extension rules relate to TCP flags.

4. A rules engine as in claim 1 wherein said extension rule table is constituted by memory within an application specific integrated circuit and said access control list table is constituted by memory external to said application specific integrated circuit.

5. A rules engine as in claim 1 wherein a chain identifier matches a plurality of rule identifiers.

6. A network unit comprising:

(1) a multiplicity of ports for receiving and forwarding addressed data packets;

(2) a lookup engine for producing forwarding data in response to address data in an addressed data packet;

(3) a post-processing engine for executing a forwarding action based on said forwarding data;

(4) a rules engine comprising:

(a) an access control list table containing entries each defining an access control list rule, a respective first action and a chain identifier; and

(b) an extension rule table for entries each defining an extension rule, a respective second action and a respective rule identifier

wherein the rules engine is operative:

(i) to search said access control list table to ascertain a match between an access control list rule and said addressed data packet;

(ii) to search said extension rule table to ascertain a match between an extension rule and said addressed data packet; and

in the event of a matched access control list rule matched to said addressed data packet, to prescribe one of:

(iiia) the respective second action associated with a matched extension rule in the event of correspondence between a chain identifier associated with the matched extension rule and a rule identifier identifying a match between that matched extension rule and said addressed data packet; or

(iiib) in the absence of said correspondence, the respective first action associated with said matched access control list rule; and

wherein said post-processing engine is operative to execute said respective first or second action as prescribed by said rules engine.

7. A network unit as in claim 6 wherein said post-processing engine executes said forwarding action in the absence of any action prescribed by said rules engine.

8. A network unit as in claim 6 wherein said access control list rules relate to fields in TCP segments and network address fields.

9. A network unit as in claim 6 wherein said extension rules relate to TCP flags.

10. A network unit as in claim 6 wherein a chain identifier matches a plurality of rule identifiers.

11. A network unit as in claim 6 wherein said extension rule table is constituted by memory within an application specific integrated circuit which includes said lookup engine and said post-processing engine and said access control list table is constituted by memory external to said application specific integrated circuit.

12. A method of operating a rules engine for the examination of selected fields in an addressed data packet, comprising:

(a) establishing an access control list table containing entries each defining an access control list rule, a respective first action and a chain identifier;

(b) establishing an extension rule table for entries each defining an extension rule, a respective second action and a respective rule identifier

(c) searching said access control list table to ascertain a match between an access control list rule and said addressed data packet;

(d) searching said extension rule table to ascertain a match between an extension rule and said addressed data packet; and

(e) in the event of a matched access control list rule matched to said addressed data packet prescribing one of:

(e1) the respective second action associated with a matched extension rule in the event of correspondence between a chain identifier associated with the matched extension rule and a rule identifier identifying a match between that matched extension rule and said addressed data packet; or

(e2) in the absence of said correspondence, the respective first action associated with said matched access control list rule.

13. A method as in claim 12 and relating said access control list rules relate to fields in TCP (Transmission Control Protocol) segments and network address fields.

14. A method as in claim 12 and relating said extension rules to TCP flags.

15. A method as in claim 12 and matching a chain identifier to a plurality of rule identifiers.