WO2009156777A1

WO2009156777A1 - Media access control (mac) address collision avoidance in ethernet switched networks

Info

Publication number: WO2009156777A1
Application number: PCT/IB2008/001641
Authority: WO
Inventors: Lars Marklund; Michael Persson; Ulf Ekstedt; Erik Walles
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2008-06-23
Filing date: 2008-06-23
Publication date: 2009-12-30

Abstract

Systems and methods according to these exemplary embodiments provide for methods and systems for reducing Medium Access Control (MAC) address collisions in Ethernet switched networks through the use of multiple MAC address.

Description

Media Access Control (MAC) Address Collision Avoidance in Ethernet Switched

Networks

TECHNICAL FIELD

[0001] The present invention relates generally to communications systems and in particular to methods and systems for reducing Medium Access Control (MAC) address collisions in Ethernet switched networks.

BACKGROUND

[0002] Communications technologies and uses have greatly changed over the last few decades. In the fairly recent past, copper wire technologies were the primary mechanism used for transmitting voice communications over long distances. As computers were introduced the desire to exchange data between remote sites grew for many purposes, such as those of businesses, individual users and educational institutions. The introduction of cable television provided additional options for increasing communications and data delivery from businesses to the public. As technology continued to move forward, digital subscriber line (DSL) transmission equipment was introduced which allowed for faster data transmissions over the existing copper phone wire infrastructure. Additionally, two way exchanges of information over the cable infrastructure became available to businesses and the public. These advances have promoted growth in service options available for use, which in turn increases the need to continue to improve the available bandwidth for delivering these services, particularly as the quality of video and overall amount of content available for delivery increases.

[0003] As the consumer electronics industry continues to mature, and the capabilities of processors increase, more devices have become available for public use that allow for the transfer of data between devices and more applications have become available that operate based on this transferred data. Of particular note are the Internet and local area networks (LANs). These two innovations allow multiple users and multiple devices to communicate and exchange data between different devices and device types. With the advent of these devices and capabilities, users increasingly desire to receive a variety of services over these networks. Some common examples of these services (or applications) are video on demand (VoD), Internet Protocol television (IPTV) and audio files. Additionally, many of these services can be received in different formats, relating to different service quality levels, based upon a variety of parameters.

[0004] Taking advantage of the ongoing improvements to communications, a

LAN may be connected to another LAN through the use of switches, e.g., Ethernet switches. A LAN enables a plurality of end user devices to communicate with each other, as well as servers external to the LAN. Typically there will be a device which acts as the controller of the LAN, such as a hub a switch or a router, for routing incoming and outgoing communication. The total number of devices that can potentially communicate with each other can be quite large by connecting a plurality of LANs together through switches, with each LAN having multiple devices associated therewith. [0005] For a communication or data packet from one end user device to reach another end user device, the address of the end user device needs to be known. One method for addressing devices is through the use of Medium Access Control (MAC) addresses. Each device has a 48 bit MAC address associated with it, e.g., the device's network interface card (NIC) can have a serial number on it which is associated with the device that the NIC is attached to, which can make the device's address almost unique. In a LAN, the controller of the LAN, e.g., a router, a hub or a switch, will typically store the MAC addresses, or a hashed value of the MAC address, of each device in its associated LAN. In this manner, when traffic is received, the hub for a LAN knows from the MAC address associated with the received traffic, whether the traffic is to be forwarded to a device in the LAN or sent to another node in the Ethernet switched network. In practice, there can be problems with this addressing solution because the 48 bit MAC address is often compressed, for example, to 12 bits, through a hashing mechanism by the Ethernet switches used to connect LANs. This compressing of the MAC address, in combination with the large number of devices which may be communicating with one another leads to a problem whereby two MAC addresses can be associated with the same compressed hash index. If a device mistakenly receives a data packet intended for another device due to the potential overlap between hashed MAC addresses (or a hub misroutes a packet for the same reason), this occurrence is referred to as a "MAC address collision". Figure 1 is a graph showing MAC address collision probabilities, where it can be seen that as the number of devices (objects) increases, the chance of collision also increases. These MAC address collisions are a concern because if a MAC address collision which cannot be resolved occurs, this can result in continuous flooding of traffic which will increase the load in the network.

[0006] Accordingly the exemplary embodiments described herein provide systems and methods for reducing MAC address collisions in networks.

SUMMARY

[0007] Systems and methods according to the present invention address this need and others by providing systems and methods for reducing MAC address collisions in networks.

[0008] According to one exemplary embodiment a device includes: a memory for storing a plurality of different Medium Access Control (MAC) addresses associated with the device; a first MAC address, selected from the plurality of MAC addresses, which is currently being used as an identifier for the device; and a processor for selectively changing from the first MAC address to a second MAC address from the plurality of the MAC addresses, wherein the second MAC address will subsequently be used as the identifier for the device.

[0009] According to another exemplary embodiment a method for changing a

MAC address within a device includes: receiving a first message which includes an instruction to change the MAC address; changing from a first MAC address taken from a plurality of different MAC addresses associated with the device to a second MAC address taken from the plurality of different MAC addresses associated with the device; and transmitting a second message including the second MAC address. [0010] According to another exemplary embodiment a method for reducing the impact of MAC address collisions in a network includes: receiving a first message which includes a first destination MAC address; determining from the first message that the first message has arrived at an incorrect destination; and transmitting, after receiving a plurality of messages from the incorrect destination over a first period of time, one of: (a) a plurality of change order messages to the first destination MAC address which include an instruction to change the first destination MAC address to a second destination MAC address and (b) a first alarm message. [0011] According to another exemplary embodiment a device includes: a communications interface for receiving a first message which includes a first destination MAC address; a processor for determining from the first message that the first message has arrived at an incorrect destination; and the communications interface transmitting, after receiving a plurality of messages from the incorrect destination over a first period of time, one of: (a) a plurality of change order messages to the first destination MAC address which include an instruction to change the first destination MAC address to a second destination MAC address and (b) a first alarm message.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings illustrate exemplary embodiments, wherein:

[0013] Figure 1 illustrates probabilities of Medium Access Control (MAC) address hash collisions according to exemplary embodiments;

[0014] Figure 2 shows an Ethernet switched network;

[0015] Figure 3 illustrates an Ethernet frame;

[0016] Figure 4 shows an Ethernet switched network including a base station according to exemplary embodiments;

[0017] Figure 5 illustrates an alternative Ethernet switched network which ca use MAC address collision systems and methods according to exemplary embodiments;

[0018] Figure 6 illustrates a communications node according to exemplary embodiments;

[0019] Figure 7 shows a method flow chart according to exemplary embodiments; and

[0020] Figure 8 shows another method flow chart according to exemplary embodiments. DETAILED DESCRIPTION

[0021] The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

[0022] As mentioned above, it is desirable to provide mechanisms and methods that reduce Medium Access Control (MAC) address collisions in networks, e.g., Ethernet switched networks. Current day Ethernet networks use twisted pair wiring or fiber optics to connect stations typically in a radial pattern. Instead of using a shared medium for multiple stations, today the shared medium is often replaced by switched Ethernet with a dedicated segment for each station. The dedicated segments connect to a switch, which may also be connected to other switches. An example of a switched Ethernet network 200 is illustrated in Figure 2, wherein a number of stations 202 are connected by means of dedicated segments 204 to Ethernet switches 206. The Ethernet switches are arranged to pick up Ethernet frames from stations or other switches and, based on information in the frame, to forward each frame over an appropriate segment.

[0023] In Ethernet networks the MAC sublayer is responsible for encapsulating data to be transmitted in frames that are assembled according to a specified Ethernet packet format. Figure 3 illustrates the format of a typical Ethernet frame 300 which includes the following fields: preamble 302 which is an alternating pattern of ones and zeros that tells the receiving stations that a frame is coming; start- of-frame delimiter 304 which has the sequence 10101011 and indicates the start of a frame; destination MAC address 306 which identifies the station(s) which should receive the frame; source MAC address 308 which identifies the sending station; an optional field VLAN 310 which is used when creating virtual LANs which use Ethernet; type 312 which indicates the type of frame being sent from an number of optional frame types; data 314 which contains the information data bits to be transmitted or received; and frame check sequence 316 which is a sequence of bits which is used to check for damaged frames.

[0024] An Ethernet switch includes a switching table that indicates on which of the switch's output ports a frame is to be output depending on the information in one or several of the frame's address fields. Usually frames are switched based on the contents of the destination MAC address fields, but many Ethernet switches also support switching based on the contents of other fields or combinations of fields, such as the source MAC address field or the VLAN tag. Of particular interest for exemplary embodiments of the present invention, a hashed MAC address relating to a specific device associated with a switch's output port can be stored in the switching (or lookup) table for use in determining when the switch should direct incoming packets toward that specific device.

[0025] In order to provide some context for this discussion, an exemplary grouping of devices of interest which can be used in an Ethernet switched network will now be described with respect to Figure 4. According to exemplary embodiments as shown in Figure 4, an Ethernet switched network 400 can include a number of devices. A base station 402 can include or be coupled to an Ethernet switch Sl 404 which includes four communications ports Pl, P2, P3 and P4 as well as communications interface 414. Those skilled in the art will appreciate that typically such a switch 404 will include more than four ports, however this reduced number is used here to simplify the discussion. Communications interface 414 (or interfaces) is shown as a generic communications interface capable of receiving a plurality of traffic types such as, for example, Ethernet frames or messages that use a MAC address as the destination address. Each of the ports Pl through P4 are in direct communications using an Ethernet cable or the like to a single device. More specifically, Pl communicates with end user device Dl 406 which is equipped with a MAC collision detection device, P2 communicates with end user device D2 408, P3 communicates with end user device D3 410 and P4 communicates with switch S2 412. Switch S2 412 also includes four ports of its own P5, P6, P7 and P8 each of which is in communications with a separate single device or virtual LAN (not shown). Using the exemplary Ethernet switched network shown in Figure 4, an example of a MAC address collision will now be described.

[0026] A MAC address collision occurs when two different MAC addresses reduce to the same hash index when a switch (or other device) hashes the 48 bit MAC address into a compressed MAC address of, e.g., 12 bits. This collision occurs, because a single hash index can thus represent two (or more) unique devices which may cause a switch to forward a message to an incorrect device. For example, suppose that a message, e.g., an Ethernet frame or packet, is received by switch Sl 404. Sl 404 hashes down the 48 bit MAC address into a 12 bit hash index which, for purely illustrative purposes, shall be referred to herein as index "ABBA". This 12 bit index is then compared to stored values in a switching table that match index values to specific ports, which in turn communicate with specific devices. In this example, index ABBA correlates with port Pl, and so the received Ethernet frame is forwarded by Sl 404 through port Pl to end user device Dl 406 which is equipped with a MAC collision detection device or unit. The end user device Dl 406 reads the destination MAC address in the received Ethernet frame and realizes that its MAC address is not the same as the destination MAC address in the received Ethernet frame. In this way, after a number of iterations have occurred which result in a number of flooding packets being received in a short time period, a MAC address collision is detected. This is an undesirable condition because it can lead to network flooding which is detrimental to a network, e.g., resource intensive. That is, in response to detection of a MAC address collision, the switch Sl 404 may "flood" the network with the received packet by sending it out over all of its ports in an attempt to identify the correct recipient of the message.

[0027] According to exemplary embodiments, an end user device Dl 406 with detection functionality is attached to an Ethernet switched network 400. Dl 406 typically operates in promiscuous mode which allows it to receive traffic from all VLANs in the network (as well as other devices in the network). Whenever unicast traffic (which is not a MAC address change order) is received by Dl 406 with a destination MAC address different from its own, the destination MAC address is stored in a collision cache (not shown) of end user device Dl 406. The collision cache can be a data structure where the entry key is the destination MAC addresses of offending nodes. The entries in the collision cache can be filtered based upon the number of received packets per time unit. For example, if no packets are received for a certain time interval tl which have the same MAC address as an earlier received packet, e.g., 1 minute, that MAC address entry is removed from the collision cache. This can occur when the MAC address has been learned by the switch S 1 404 and flooding associated with that particular MAC address has ceased. [0028] If after time interval t2, e.g., 10 minutes, the same MAC address entry still exists in the collision cache, i.e., indicative of an unhandled collision rather than an as yet, unlearned MAC address. Exemplary embodiments provide for the system to take corrective action. This corrective action may be taken by end user device Dl 406 and can include for example initiating a notification for an automatic change of MAC address in the relevant equipment, e.g., the other device which has a MAC address which has the same hash index as that associated with Dl 406. Alternative correction action could include the issuing of an alarm al to the network operator. Alarm al can include an alarm name "MAC collision detected" as well as the MAC address of the node which needs to change its MAC address.

[0029] According to exemplary embodiments, the MAC address of the relevant equipment can either be changed manually or automatically. For a manual MAC address change, after receiving the alarm al, the network operator issues a command to the relevant end user equipment which changes the current MAC address to, e.g., the next one in a stored list of MAC addresses. In the case of the automatic MAC address change, the detecting end user equipment Dl 406 (or alternatively the operator after receiving alarm al) can automatically send a burst of change order messages to the relevant end user equipment. The end user equipment will change its MAC address to the next MAC address in its stored list. Only the first received change order received from Dl 406 will be acted upon by the end user equipment, since the subsequently received change orders will be destined to the old MAC address and will be discarded. While this burst of change order messages can cause some flooding in the network, this flooding will not trigger an alarm in the network at least because the flooding time period is less than time period tl . When an automatic MAC address change is initiated, by either the operator or the end user device Dl 406, and the flooding persists after time t3, an alarm a2 is issued from Dl 406 to the network operator. Time t3 can be described, for example, as shown below in equation

(1): t3 = n * t2 (1) where n is the number of MAC addresses per end system. For the case when the relevant, i.e., offending end user device, does not have the ability to change its MAC address in accordance with received instructions, different solutions can be used. For example, when the operator sees that the relevant device does not have the ability to change its MAC address another port on the equipment could be used, the network interface board could be changed, or possibly the entire relevant device could be replaced.

[0030] According to exemplary embodiments, each node in a network with a

MAC address can have a list of a plurality of different MAC addresses, for example, seven MAC addresses. These MAC addresses can be changed according to the exemplary embodiments described above. Upon changing a MAC address, a node or end user equipment can, for example, issue a gratuitous Address Resolution Protocol (ARP) message to notify other nodes in the network of its MAC address change. Any lost packets can typically be handled by higher order protocols used by the network, e.g., Transport Control Protocol (TCP).

[0031] While the above described exemplary embodiments have been described with respect to the network shown in Figure 4, as will be appreciated by one of skill in the art, the present invention may be used in other networks where MAC address collisions could occur. For example, as described in U.S. Patent Number 7,228,072 B2, there is a system and method for integrating a fiber optic fixed access network and a fiber optic radio access network as shown in Figure 5. Communication system 500 can include a first multiplexing unit 510 which is in communications with a number of radio units (RUs) 514 which are further in communication with mobile systems 516. Additionally, first multiplexing unit 510 is in communication with multiple fixed access subscribers 512 over a fiber optic connection. To facilitate communications with both the RUs 514 and the fixed access subscribers 512, the first multiplexing unit 510 includes both a radio course wave division multiplexing (CWDM) module and an Ethernet switch respectively. First multiplexing unit 510 also has an optical CWDN input/output (I/O) module which is used to communicate over, typically, a fiber optic fixed access network 508 to a second multiplexing unit 506. Both multiplexing units 510 and 506 are capable of demultiplexing as well, which leads to the second multiplexing unit 506 to have similar components and functionality as the first multiplexing unit 510. Additionally, the second multiplexing unit 506 is in communications with both a main unit 504, which includes the digital baseband components of a base station, and a router 502 for further transporting and receiving Ethernet frames within the network.

[0032] As can be seen in Figure 5, through the use of switches, routers and the devices which are used at the fixed access subscriber locations, a large number of end user devices with different MAC addresses can exist. Therefore, the exemplary embodiments described above with respect to solving the problem of MAC address collisions within an Ethernet switched network could also be applied to the communication system 500 that is illustrated in Figure 5.

[0033] The exemplary embodiments described above illustrate methods and systems for reducing MAC address collisions in Ethernet switched networks. An exemplary communications node 600, e.g., end user device Dl 406 which is equipped with a MAC collision detection device, will now be described with respect to Figure 6. Communications node 600 can contain a processor 602 (or multiple processor cores), memory 604, one or more secondary storage devices 606, a software application (or multiple applications) 608 and an interface unit 610 to facilitate communications between communications node 600 and the rest of the network. The interface unit 610 can, for example, support an Ethernet connection and the memory 604 or secondary storage devices 606 can be used to store collision information or the device's list of a plurality of different MAC addresses. The software application 608 in conjunction with the processor 602 and memory 604 can execute instructions and perform functions used to trigger alarm messages and/or transmit instructions to a device for changing its MAC address, which have been described above. [0034] Utilizing the above-described exemplary systems according to exemplary embodiments, a method for reducing MAC address collisions is shown in the flowchart of Figure 7. Initially a method for changing a MAC address within a device includes: receiving a first message which includes an instruction to change the MAC address in step 702; changing from a first MAC address taken from a plurality of different MAC addresses associated with the device to a second MAC address taken from the plurality of different MAC addresses associated with the device in step 704; and transmitting a second message including the second MAC address in step 706.

[0035] Utilizing the above-described exemplary systems according to exemplary embodiments, a method for reducing a MAC address collision is shown in the flowchart of Figure 8. Initially a method for reducing the impact of a MAC address collision in a network includes: receiving a first message which includes a first destination MAC address in step 802; determining from the first message that the first message has arrived at an incorrect destination in step 804; and transmitting, after receiving a plurality of messages from the incorrect destination over a first period of time, one of: (a) a plurality of change order messages to the first destination MAC address which include an instruction to change the first destination MAC address to a second destination MAC address and (b) a first alarm message in step 806. [0036] The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. These variations are intended to illustrate that the functions of power scaling, adjustment factor computation and correction factor computation can reside within the same piece of hardware, different pieces of hardware, be performed by software or any combination thereof as desired. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article "a" is intended to include one or more items.

Claims

WHAT IS CLAIMED IS;

1. A device (600) comprising: a memory (604) for storing a plurality of different Medium Access Control (MAC) addresses associated with said device (600); a first MAC address, selected from said plurality of MAC addresses, which is currently being used as an identifier for said device; and a processor (602) for selectively changing from said first MAC address to a second MAC address from said plurality of said MAC addresses, wherein said second MAC address will subsequently be used as said identifier for said device.

2. The device of claim 1, further comprising: a communications interface for transmitting and receiving data.

3. The device of claim 2, wherein said processor, upon receipt of an instruction to said first MAC address, selectively changes from said first MAC address to said second MAC address within said plurality of said MAC addresses.

4. The device of claim 1, wherein said device is equipped with a MAC collision detection unit.

5. A method for changing a MAC address within a device (600) comprising: receiving a first message which includes an instruction to change said MAC address; changing from a first MAC address taken from a plurality of different MAC addresses associated with said device (600) to a second MAC address taken from said plurality of different MAC addresses associated with said device; and transmitting a second message including said second MAC address.

6. The method of claim 5, wherein said second message is a gratuitous address resolution protocol (ARP) message.

7. The method of claim 5, further comprising: storing said plurality of MAC addresses within said device.

8. The method of claim 5, wherein further messages transmitted after said second message include said second MAC address.

9. A method for reducing the impact of MAC address collisions in a network comprising: receiving a first message which includes a first destination MAC address; determining from said first message that said first message has arrived at an incorrect destination; and transmitting, after receiving a plurality of messages from said incorrect destination over a first period of time, one of: (a) a plurality of change order messages to said first destination MAC address which include an instruction to change said first destination MAC address to a second destination MAC address and (b) a first alarm message.

10. The method of claim 9, further comprising: transmitting a second alarm message if more messages are received for said first destination MAC address after a second predetermined period of time.

11. The method of claim 9, wherein said first alarm message includes information about said incorrect destination and is transmitted to a network operator.

12. The method of claim 9, wherein said first message is at least one of a frame or a packet.

13. A device (600) comprising: a communications interface (610) for receiving a first message which includes a first destination MAC address; a processor (602) for determining from said first message that said first message has arrived at an incorrect destination; and said communications interface (610) transmitting, after receiving a plurality of messages from said incorrect destination over a first period of time, one of: (a) a plurality of change order messages to said first destination MAC address which include an instruction to change said first destination MAC address to a second destination MAC address and (b) a first alarm message.

14. The device of claim 13, wherein said communications interface further transmits a second alarm message if more messages received for said first destination MAC address after a second predetermined period of time.

15. The device of claim 13, wherein said first alarm message includes information about said incorrect destination and is transmitted to a network operator.

16. The device of claim 13, wherein said first message is at least one of a frame or a packet.