Disposition filtering of messages using a single address and protocol table bridge

• US 5,515,513 A
• Filed: 03/23/1995
• Issued: 05/07/1996
• Est. Priority Date: 04/08/1991
• Status: Expired due to Term

• Current Assignee: Enterasys Networks Incorporated (Extreme Networks, Inc.)
• Original Assignee: Digital Equipment Corporation (HP Inc.)
• Inventors: Vacon, Gary, Metzger, Stephen D., Lomicka, Jeffrey A., Gili, Pat
• Primary Examiner(s): Lee, Thomas C.
• Assistant Examiner(s): DINH, DUNG C
• Application Number:
  US08/410,546
• Time in Patent Office: 411 Days
• Field of Search: 395/200.16, 395/200.15, 370/85.13
• US Class Current: 709/249
• CPC Class Codes: H04L 12/4625 Single bridge functionality, e.g. connection of two networks over a single bridge
• CPC Class Codes: H04L 45/742 Route cache; Operation thereof
• CPC Class Codes: H04L 45/745 Address table lookup; Address filtering

Abstract

An arrangement for selective filtering, e.g. one-way filtering, of messages received by a 2-port bridge from stations connected to two LANs of an extended LAN is provided. The bridge includes a message filtering database containing the addresses of all stations connected to one of the LANs. The database also contains a list of higher-level protocols employed by the stations. Associated with each protocol-type is information used by the bridge to dispose of the message. The message filtering database comprises a single table memory capable of supporting both ports of the bridge. The selective filtering process involves a two-step analysis by the bridge to determine whether to discard the message or forward it to another port. The analysis is based on a destination address and a protocol-type of the received message.

Claims

1. Bridging apparatus having two ports for coupling to a first medium and a second medium, said apparatus providing selective filtering of messages transmitted between stations on said media, each of said messages including a destination address and a protocol-type code, said apparatus comprising:

means for receiving a message from said first medium;

a single content addressable memory (CAM) table for storing a message filtering database, said single CAM table having a plurality of database entries capable of supporting each of the two ports of said apparatus, said database entries including;

a first portion of entries containing addresses of the stations connected to only one of said first and second media; and

a second portion of entries containing protocol-types within the stations connected to said first and second media, said second portion of entries having asserted first and second flags to distinguish said protocol-types from said addresses;

storage means for storing disposition information associated with each of said protocol-types stored in said database entries;

means for comparing said received message with said addresses and protocol-types stored in said database entries; and

means responsive to said comparison means for selectively disposing of each received message in accordance with said disposition information, said selectively disposing means forwarding said message to said second medium when one of;

said protocol-type of said message does not match one of said protocol-types of said database entries; and

said protocol-type of said message matches one of said protocol-types of said database entries and said disposition information associated with said protocol-type specifies forwarding said message to said second medium.

2. A bridge for coupling a first network to a second network, said bridge comprising:

a bus;

a message filtering database coupled to said bus, said message filtering database having a plurality of database entries including;

address entries containing addresses of the stations connected to one of said networks; and

protocol-type entries containing protocol-types within the stations connected to said one network;

a memory, coupled to said bus, for storing disposition information associated with each of protocol-type entry;

a plurality of port controllers, coupled to said bus, for receiving and transmitting a message between said networks, said port controllers configured to perform direct memory access (DMA) requests in said memory; and

a multi-stage control unit, coupled to said bus, for executing message filtering operations of said bridge in response to said DMA requests.

3. The bridge of claim 2 wherein said multi-stage control unit comprises a memory allocation stage for responding to DMA requests from said port controllers in response to reception of said message, said memory allocation stage initiating time-multiplexed transfer of said message over said bus to said memory.

4. The bridge of claim 3 wherein said multi-stage control unit further comprises an address filtering stage, coupled to said memory allocation stage, for executing time-multiplexed comparison operations between a destination address of said message and said address entries of said database over said bus.

5. The bridge of claim 4 wherein said multi-stage control unit further comprises a protocol-type filtering stage, coupled to said address filtering stage, for executing time-multiplexed comparison operations between a protocol-type of said message and said protocol-type entries of said database over said bus in response to a match between said destination address and one of said address entries.

6. The bridge of claim 5 wherein said multi-stage control unit further comprises a message disposition stage for disposing,of said message in accordance with results of said address filtering and protocol-type filtering stages.

7. A bridge for coupling a first network to a second network, said bridge comprising:

a bus;

a message filtering database coupled to said bus, said message filtering database having a plurality of database entries including;

address entries containing addresses of the stations connected to one of said networks; and

protocol-type entries containing protocol-types within the stations connected to said one network;

a memory, coupled to said bus, for storing disposition information associated with each of protocol-type entry;

a plurality of port controllers, coupled to said bus, for receiving and transmitting a message between said networks, said port controllers configured to perform direct memory access (DMA) requests in said memory; and

a multi-stage control unit, coupled to said bus, for executing message filtering operations of said bridge, said control unit including;

a memory allocation stage for responding to DMA requests from said port controllers in response to reception of said message, said memory allocation stage initiating time-multiplexed transfer of said message over said bus to said memory;

an address filtering stage, coupled to said memory allocation stage, for executing time-multiplexed comparison operations between a destination address of said message and said address entries of said database over said bus;

a protocol-type filtering stage, coupled to said address filtering stage, for executing time-multiplexed comparison operations between a protocol-type of said message and said protocol-type entries of said database over said bus in response to a match between said destination address and one of said address entries; and

a message disposition stage for disposing of said message in accordance with results of said address filtering and protocol-type filtering stages.

8. A method for filtering a message received at a bridge from a source station coupled to a first network and destined for a destination station coupled to a second network, said bridge connecting the first network to the second network, said method comprising the steps of:

(A) comparing a destination address of the received message with address entries contained in a message filtering database, said message filtering database containing only addresses of stations connected to the first network;

discarding the received message if said destination address of the received message matches any of said address entries contained in said message filtering database;

(B) comparing a protocol-type of the received message with protocol-type entries contained in said message filtering database if said destination address of the received message does not match any of said addresses contained in said message filtering database;

forwarding the received message to the second network if said protocol-type of the received message does not match any of said protocol-type entries contained in said message filtering database; and

disposing of the received message in accordance with disposition information, associated with each of said protocol-type entries, stored in said bridge if said protocol-type of the received message matches any of said protocol-type entries contained in said message filtering database.

9. The method of claim 8 wherein said step of disposing of the received message in accordance with said disposition information comprises the step of discarding the received message.

10. The method of claim 8 wherein said step of disposing of the received message in accordance with said disposition information comprises the step of discarding the received message only if the message is a multicast message.

11. Bridging apparatus having two ports for coupling to a first medium and a second medium, said apparatus providing selective filtering of messages transmitted between stations on said media, each of said messages including a destination address and a protocol-type code, said apparatus comprising:

A. means for receiving a message from said first medium;

B. a single table for storing a message filtering database, said single table having a plurality of database entries capable of supporting each of the two ports of said apparatus, said database entries comprising

B1. a first portion of entries containing addresses of the stations connected to only one of said first and second media; and

B2. a second portion of entries containing protocol-types within the stations connected to said first and second media,

C. storage means for storing disposition information associated with each of said protocol-types stored in said database entries;

D. means for comparing said received message with said addresses and protocol-types stored in said database entries;

E. means responsive to said comparison means for selectively disposing of each received message in accordance with said disposition information by forwarding said message to said second medium when one of

said protocol-type of said message does not match one of said protocol-types of said database entries; and

said protocol-type of said message matches one of said protocol-types of said database entries and said disposition information associated with said protocol-type specifies forwarding said message to said second medium.