Content addressable memory organized to share entries between different entities such as ports of a network unit
Assignee3Com Corporation
InventorsDaniel Martin O'Keeffe, Eugene O'Neill, Edele O'Malley, Eoin O'Brien
Life of this patent
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Abstract
A content addressable memory stores entries each comprising a rule and as part of the entry a mask identifying all the entities to which the rule is applicable. A search pattern of data and a bit mask identifying the actual entity (or entities) associated with the data is applied as a search word along with a comparison mask that excludes all the other entities from the comparison of the search word with the entry. The CAM can thereby store efficiently in a single entry a rule that may be applicable to some but not all of a multiplicity of entities such as possible ingress ports of a network unit.
Claims10
A method of operating a content addressable memory in the examination of a selected portion of a packet for conformity with at least one rule, comprising:
- (a) storing the rule in a first segment of a data line of the content addressable memory;
- (b) storing in a second segment of said data line a port bit mask identifying to which network unit ports said one rule is applicable;
- (c) identifying at least one particular port;
- and
- (d1) applying to the content addressable memory a word which comprises said selected portion in respect of said first segment;
- and in respect of said second segment a search bit pattern that selects said at least one port and masks other ports;
- and
- (d2) applying to said content addressable memory a comparison mask which excludes all said other ports from a comparison of the word with the contents of the content addressable memory.
A rules engine for the examination of a selected portion of a packet for conformity with at least one rule, the rules engine comprising:
- (a) a content addressable memory organized for storing the rule in a first segment of a data line of the content addressable memory and for storing a bit pattern in a second segment of said data line, said bit pattern specifying all network unit ports to which said rule is applicable;
- and
- logic organized:
- (i) to identify at least one particular entity port;
- (ii) to apply to the content addressable memory a word which comprises said selected portion in respect of said first segment;
- and in respect of said second segment a search bit pattern that selects said at least one port and masks other ports;
- and
- (iii) to apply to said content addressable memory a comparison mask which excludes all said other ports from a comparison of the word with the contents of the content addressable memory.
A network unit comprising:
- a multiplicity of ports for receiving and forwarding data packets;
- and
- a rules engine for the examination of a selected portion of a data packet in said network unit for conformity with at least one rule, the rules engine comprising:
- a) a content addressable memory organized for storing the rule in a first segment of a data line of the content addressable memory and for storing a port bit mask in a second segment of said data line, said port bit mask specifying all the ports to which said rule is applicable;
- and
- logic responsive to said data packet and organized:
- (i) to identify at least one particular port for the packet;
- (ii) to apply to the content addressable memory a word which comprises said selected portion in respect of said first segment;
- and in respect of said second segment a search bit pattern that selects at least one port and masks other ports;
- and
- (iii) to apply to said content addressable memory a comparison mask which excludes all said other ports from a comparison of the word with the contents of the content addressable memory.
A rules engine for the examination of a selected portion of a data packet received by a network unit, which has a multiplicity of ports, for conformity with at least one rule, the rules engine comprising:
- (a) a content addressable memory organized for storing the rule in a first segment of a data line of the content addressable memory and for storing a port bit pattern in a second segment of said data line, said port bit pattern specifying all the ports to which said rule is applicable;
- and
- logic responsive to a packet and organized:
- (i) to identify at least one particular port for the packet;
- (ii) to apply to the content addressable memory a word which comprises said selected portion in respect of said first segment;
- and in respect of said second segment a search bit pattern that selects at least one port and masks other ports;
- and
- (iii) to apply to said content addressable memory a comparison mask which excludes all said other ports from a comparison of the word with the contents of the content addressable memory.
A network unit comprising:
- a multiplicity of ports for receiving and forwarding data packets;
- and
- a rules engine for the examination of a selected portion of a data packet received by a said network unit for conformity with at least one rule, the rules engine comprising:
- (a) a content addressable memory organized for storing the rule in a first segment of a data line of the content addressable memory and for storing a port bit mask in a second segment of said data line, said port bit mask specifying all the ports to which said rule is applicable;
- and
- logic responsive to a packet and organized:
- (i) to identify at least one particular port for the packet;
- (ii) to apply to the content addressable memory a word which comprises said selected portion in respect of said first segment;
- and in respect of said second segment a search bit pattern that selects at least one port and masks other ports;
- and
- (iii) to apply to said content addressable memory a comparison mask which excludes all said other ports from a comparison of the word with the contents of the content addressable memory.
Dependencies are inferred from the claim text.