WO2004047384A1

WO2004047384A1 - Processing data packets within a data switch

Info

Publication number: WO2004047384A1
Application number: PCT/SG2002/000269
Authority: WO
Inventors: Yean Kee Yong; Alvin Lim Swee Hock
Original assignee: Infineon Technologies Ag
Priority date: 2002-11-15
Filing date: 2002-11-15
Publication date: 2004-06-03
Also published as: DE10297815T5; TWI241806B; DE10297815B4; AU2002368361A1; TW200423636A

Abstract

A data switch such as an Ethernet switch compares the address contained in a received packet with addresses in MAC address table, to identify whether the table associates a port with the address. If such a match is found, the switch transmits the data packet through the port specified by the MAC address table. If not, the Ethernet switch processes the data packet according to whether the address is in a list of reserved addresses stored inside the switch.

Description

Processing data packets within a data switch

Field of the invention

The present invention relates to a data switch such as an ethernet switch which switches data packets containing an address.

Background of Invention

It is well known to provide a data switch having a plurality of ports for receiving and transmitting data packets. Two or more ports of the switch are connected to respective devices (possibly via intermediate devices and/or networks), and these devices each have an address known as a MAC address. Each of the data packets includes the MAC address of the device it is intended to go to, and it is the job of the switch to ensure that the packet is transmitted through the port leading to the corresponding device.

Conventionally, the switch is designed to generate automatically an address table associating MAC addresses with its various ports, so that, when a data packet is received, the data switch can extract the address, and use it and the address table to identify the associated port. The data packet is then transmitted through that port. The address table is stored in read/write memory, so that it can be modified as required.

This is not the only function of the addresses, however. IEEE standard 802.1 defines certain "reserved" addresses which are not to be used as the MAC addresses of any devices. A packet with one of these addresses is not supposed to be transmitted by the switch. Instead, the address determines a function which the switch should perform on the data packet. For example, it may be a data packet containing control signals for modifying the operating parameters of the switch. In another example, the address tells the switch to transmit the packet through a predefined port (i.e. irrespective of the data stored in the MAC address table for that port). When the switch receives a data packet it firstly checks whether the address is one of these predefined addresses. If it is, then it is unnecessary to compare the address to the address table. That is, instead of comparing the address in the data packet to the address table, the switch performs the function defined by the address, e.g. to extract any relevant information in the data packet (e.g. the control signals mentioned above) and then discard the data packet.

Summary of the Invention

The present invention is based on the inventors' realisation that, as the standards governing data switches change over time, the reserved addresses allocation space may also change. For this reason, certain addresses in the reserved list may be used by certain vendors for specific functions. However, if the reserved address list has been hard coded into the switch with a action which is different from the new function of the address, the switch would not be able to transmit such data packets correctly.

Accordingly, the present invention proposes in general terms that, even for data packets including a destination address which is in the reserved table, the destination address is compared with a read/write table which defines actions associated with addresses. If such a match is found, the switch implements the actions specified by the read/write table, even if the address is in a reserved address list stored inside the switch.

Thus the invention makes it possible for a data switch to correctly transmit data packets even if they contain addresses which were on the reserved list at the time that the data switch was constructed. Note that this capability is achieved at a cost: unlike the prior art switch described, the data switch of the invention typically has to perform a comparison of the addresses in all received packets with a read/write table. In the case that the list of revised addresses is never changed, then many of these comparisons will be pointless: no match will ever be found between the address table and a address on the reserved list.

The present invention makes it possible to have two methods for handling packets including the reserved addresses: as a default mode, e.g. to drop the packet, or according to data stored in the address table.

In the case that the standard is modified to remove addresses from the reserved list, or to modify their function, this modification in the function of the switch can be performed by a modification of the read/write table, e.g. performed by applying external control signals to the switch. Note, however, that the user does not have to take any action in the case that the user decides not to process addresses on the reserved list. If packets do not have an address which appears in the read/write table, they will automatically be dropped.

The invention makes it possible to change the processing associated with addresses on the reserved list. For example, it is possible to modify the read/write table to specify that a predetermined port is associated with one of the addresses on the reserved list. In this case, instead of discarding a packet having this reserved address (the default mode), the switch will always forward it to the predefined port.

More generally, for additional flexibility, the read/write table can be programmed with these reserved addresses, and with a set of actions associated with each entry. The actions defined in the read/write table supersede the actions defined in the default mode. Preferably, the read/write table is the address table used by the switch to control the switching fabric of the device.

In this case, preferably upon receiving a data packet, the switch performs a lookup in the address table, as well as a comparison of the address with the list of reserved addresses. In the case that a match is found in the address table, then the packet is forwarded based on the actions defined in the address table, irrespective of whether the address is part of the reserved address list.

Another possibility, however, is for the read/write table to be a second table, separate from the address table used by the control unit of the switching fabric. In this case, when a data packet is received its destination address may first be compared with the list of reserved addresses. If there is no match, the packet is processed in the usual way based on the address table in the switch. If there is a match, however, the destination address is compared to the second table. If there is a match, the packet is dealt with as defined by the second table. If there is no match, the packet is dealt with according to the reserved address list.

The second table may, for example, be associated with a monitoring port of the switch. In the case that a match is found between the destination address of a received packet and the reserved address list, the data packet may be transmitted to the monitoring port. In the case that a match is found between the destination address of the received packet and the second table, the data packet is dealt with as specified by the second table. For example, it may be forwarded to a port of the switch defined by the second table. Otherwise, the data packet may be discarded. Brief Description of The Figures

Preferred features of the invention will now be described, for the sake of illustration only, with reference to the following figure in which:

Fig. 1 is a flow diagram of a first method according to the present invention; and

Fig. 2 is a flow diagram of a second method according to the invention.

Detailed Description of the embodiments

As shown in Fig. 1 , a method which is an embodiment of the invention includes a step 1 of receiving a data packet. The address in the data packet is extracted in step 2. In step 3, the address is compared with an address table stored in read/write memory, and the address is compared with a reserved list stored in write-only memory. These two actions are preferably performed in parallel.

In step 4, it is determined whether step 3 identified a match between the address and the address table. In this case the function defined by the address table is performed (step 5).

Otherwise, the method proceeds to step 6, in which it is determined whether step 3 identified a match between the address and the reserved list. In this case the function defined by the reserved list is performed (step 7).

Otherwise, the method proceeds to step 8 in which the address is treated as not recognised. In this case, the packet is treated as in the prior art systems when a packet with an unrecognised address was received. For example the packet may be broadcast through all ports (or all ports apart from the one through which it was received). The method steps of an alternative, and presently less preferred, method according to the invention are shown in Fig. 2.

The method of Fig. 2 includes a step 11 of receiving a data packet. The address in the data packet is extracted in step 12. In step 13, the address is compared with a reserved list stored in write-only memory.

In step 13, no match between the address and the reserved list, the address is compared to an address table (as in prior art methods), and the data packet is transmitted to one of the ports according to data extracted from the address table using the address.

However, if in step 13 a match is found between the address and the reserved list, the data packet is sent to a predefined "monitoring port" of the switch. There the address is compared with a second read/write table in step 14.

If is determined in step 14 that there is a match between the address and the second table, a function is performed which is defined by the second read/write table and associated with that address (step 15). For example, the second read/write table may specify that data packets carrying that address are forwarded to a respective other one of the ports.

Otherwise, the function defined by the reserved list is performed (step 16).

Note that the first of the two embodiments is preferred since it means that a second read/write memory is not required. Furthermore, the time taken by data packets to pass through the switch is typically lower for the first embodiment than the second. Although only two embodiments of the invention has been described, the invention is not limited in this respect and many variations are possible within the scope of the invention as will be clear to a skilled reader.

Claims

1. A data switch for receiving and transmitting data packets, the data switch comprising:

a plurality of ports for receiving/transmitting data packets which each include an address;

table means for storing modifiable associations between addresses and corresponding ports;

reserved address identification means for determining if addresses included in received packets are one of a set of predetermined addresses; and

table match identification means for determining if addresses included in received packets are one of the addresses associated by the table with corresponding ports;

wherein the data switch is arranged, in the case that the table match identification means identifies a match for a given packet to process that data packet according to data associated with the address in the table, and otherwise in the case that the reserved address identification means determines that the address is one the predetermined addresses to process the packet in accordance with data associated with that predetermined address.

2. A method for processing data packets in a data switch, the method comprising:

(a) receiving a data packet including an address, and extracting the address; (b) determining if the address is one of a number of addresses associated by a table with corresponding ports;

(c) in the case that the determination in step (b) is positive to process that data packet according to the association given by the table,

(d) in the case that the determination in step (b) is negative to process the data packets according to whether the address is one of a set of predetermined reserved addresses.

3. A method according to claim 2 including a step, performed with step (b), of determining if the address is one of the set of predetermined reserved addresses.

4. A data switch for receiving and transmitting data packets, the data switch comprising:

reserved address identification means for determining if addresses included in received packets are one of a set of predetermined addresses;

table means for storing modifiable associations between addresses and corresponding ports; and

wherein the data switch is arranged, in the case that the reserved address identification means determines that the address is one the predetermined addresses, to transmit the table to the table match identification means, and in the case that the table match identification means identifies a match for a given packet to process that data packet according to data associated with the address in the table, and otherwise in the case that the reserved address identification means determines that the address is one the predetermined addresses to process the packet in accordance with data associated with that predetermined address.

5. A data switch according to claim 4 in which the table match identification means is associated with one of the ports.

6. A method for processing data packets in a data switch, the method comprising:

(a) receiving a data packet including an address, and extracting the address;

(b) determining if the address is one of a set of predetermined reserved addresses;

(c) in the case that the determination in step (b) is positive to process the data packets according to whether the address is one of a number of addresses included in a read/write table.

7. A method according to claim 2, claim 3 or claim 6 including a step preceding step (a) of modifying the table in respect of certain addresses to obtain a function to be performed if the data packet includes one of the certain addresses.