Abstract:
Reservation, request, allocation, assignment and application protocols for conserving addresses requiring unique allocation from a finite address domain. In accordance with the protocols, a set of addresses within the domain are reserved for “intra-switch only” applications so as to be to allocable to a plurality of organizations for assignment and application in a plurality of switches without introducing addressing ambiguities into networks. Other addresses within the domain not having the “intra-switch only” restriction are reserved for a single organization so as to be assigned and applied in a single device to avoid introducing addressing ambiguities into networks. The addresses may be MAC addresses.

Description:
BACKGROUND OF THE INVENTION 
   Network equipment manufacturers assign 48-bit identifiers called media access control (MAC) addresses to network devices they make. MAC addresses are allocated to manufacturers in blocks by the Institute of Electrical and Electronics Engineers, Inc. (IEEE) Registration Authority. All MAC addresses in an allocated block include the same three-byte “organizationally unique identifier” (OUI) reserved for the manufacturer. 
   The allocation of MAC addresses with OUIs is intended to encourage interoperability of network devices. If network devices made by different manufacturers applied in the same network are to communicate unambiguously through exchange of MAC-addressed frames, each network device must be assigned a MAC address that is unique. And since it is not known a priori in which network a device will be applied, each manufacturer must assign to a network device a MAC address which is unique among not only its own manufactured devices, but unique among network devices made by other manufacturers as well. Such global uniqueness is guaranteed by allocating MAC addresses having OUIs. 
   Although most MAC addresses are used for communication between network devices, as outlined above, use of MAC addresses exclusively within a single network device is becoming more common. One such “internal only” use of MAC addresses arises in the context of exceptional frame forwarding within a LAN switch. Generally speaking, a LAN switch is a multi-port LAN device which interconnects LAN end-stations residing in different LAN broadcast domains, or LAN segments, through different ports on the switch. Such a switch typically forwards conventional frames received from a source end-station over a first port to a destination end-station over a second port based on MAC addressing information encoded in the frame and the switch&#39;s knowledge of the port through which the destination end-station can be reached. Such a switch may, however, depart from convention when forwarding certain exceptional frames. To perfect exceptional frame forwarding, MAC addresses may be temporarily assigned to interfaces or ports of the switch and encoded in exceptional frames upon internal transmission to cause such frames to be captured by such interfaces or ports. Such temporarily assigned and encoded MAC addresses are never “seen” on an external LAN transmission medium; they are only “seen” internally. 
   Because MAC addresses applied in “internal only” uses are never “seen” outside the network device to which they are assigned, maintaining their global uniqueness among network equipment manufacturers to avoid addressing ambiguities is not necessary. Manufacturers nonetheless often assign globally unique MAC addresses (i.e. allocated by the IEEE Registration Authority and having the manufacturer&#39;s globally unique OUI) for “internal use only” applications in network devices, reducing the number of globally unique MAC addresses remaining in the available MAC address pool unnecessarily. 
   As described in Internet Engineering Task Force Requests for Comment (IETF RFCs) 1062, 1122 and 1700, it is known in the context of Internet Protocol (IP) addressing to reserve the network number “127” for a host “loopback” function for use on any IP host such that any IP datagram having a network “127” address loops-back inside the host and never appears on any IP network. However, IP host loopback addressing is directed to a Layer  3  (i.e. routing) protocol. Moreover, there is no suggestion to assign loopback addresses to switching devices or applying such addresses in special processing of inbound datagrams. 
   As described in RFC 2464, it is also known to locally administer MAC addresses by setting a “U/L” bit at a particular bit position in the 48-bit address. However, locally administered MAC addresses are not reserved for “internal only” uses and may be encoded in frames transmitted on external LAN media. 
   Accordingly, it would be desirable to implement a reservation, allocation, assignment and application protocol for networking addresses, such as MAC addresses, which takes advantage of the fact that addresses used exclusively in internal applications would not cause addressing ambiguities even if assigned to a plurality of devices in the same network. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention provides reservation, request, allocation, assignment and application protocols for conserving networking addresses in a finite address domain wherein a portion of the addresses must be uniquely allocated. In accordance with the protocols, a first set of addresses within the domain are reserved for “internal use only” and are allocable to a plurality of organizations for assignment and application in a plurality of devices without risking the introduction of addressing ambiguities into communication networks. A second set of addresses within the domain and not having the “internal use only” restriction are reserved for a single organization and are assigned and applied in a single network device to avoid risking the introduction of addressing ambiguities into networks. The “internal use only” addresses are preferably “intra-switch only” addresses and are allocable to a plurality of organizations for assignment and application in a plurality of switches. The addresses are preferably MAC addresses. 
   These and other aspects of the present invention may be better understood by reference to the following detailed description taken in conjunction with the drawings briefly described below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a conceptual level diagram illustrating request, allocation assignment and application protocols for MAC addresses in accordance with a preferred embodiment of the invention; 
       FIG. 2  is a block diagram of a LAN switch in which MAC addresses allocated in accordance with a preferred embodiment of the invention may be assigned and applied; 
       FIG. 3  is a diagram of a conventional frame upon receipt by the LAN switch according to  FIG. 2  from a LAN in an exemplary application protocol; 
       FIG. 4  is a diagram of a conventional frame upon transmission on the backplane of the LAN switch according to  FIG. 2  in an exemplary application protocol; 
       FIG. 5  is a diagram of a conventional frame upon transmission by the LAN switch according to  FIG. 2  to a LAN in an exemplary application protocol; 
       FIG. 6  is a diagram of an exceptional frame upon receipt by the LAN switch according to  FIG. 2  from a LAN in an exemplary application protocol; 
       FIG. 7  is a diagram of an exceptional frame upon transmission on the backplane of the LAN switch according to  FIG. 2  by a network interface in an exemplary application protocol; 
       FIG. 8  is a diagram of an exceptional frame upon retransmission on the backplane of the LAN switch according to  FIG. 2  by the management interface; 
       FIG. 9  is a diagram of an exceptional frame upon transmission by the LAN switch according to  FIG. 2  to a LAN in an exemplary application protocol; 
       FIG. 10  is a flow diagram of reservation, request and allocation protocols for MAC addresses in accordance with a preferred embodiment of the invention; and 
       FIG. 11  is a flow diagram of assignment and application protocols for MAC addresses in accordance with a preferred embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , preferred reservation, request, allocation and application protocols for MAC addresses are shown at a conceptual level. MAC address domain  100  includes address ranges reserved for LAN equipment manufacturer LEM 1   110  (LEM 1 R addresses), for LAN equipment manufacturer LEM 2   120  (LEM 2 R addresses) and for “intra-switch only” applications (ISR addresses). LEM 1 R and LEMR 2  address ranges are reserved by assigning LEM 1   110  and LEM 2   120  a three-byte identifier (OUI) and following a convention that all addresses having an OUI as the first three bytes are reserved for the LAN equipment manufacturer to which the OUI has been assigned. Thus, for example, all MAC addresses in the range “00-20-DA-xx-xx-xx” may be reserved for Alcatel Internetworking, Inc., the assignee hereof, by assigning Alcatel Internetworking, Inc. the OUI “00-20-DA”. ISR addresses may be used by any LAN equipment manufacturer but are reserved for “internal use only” within LAN switches. ISR addresses may be reserved by assigning an N-byte identifier outside the range of any OUI assigned to a LAN equipment manufacturer and following a convention that all addresses having the N-byte identifier are reserved for “internal use only”. 
   In a preferred request-and-allocation protocol, LAN equipment manufacturers request MAC address allocation and are, generally speaking, allocated blocks of MAC addresses within the range of their assigned OUIs. Thus, as shown, LEM 1   110  requests allocation of MAC addresses and in response is allocated a block of addresses within the LEM 1 R address range. LEM 2   120  requests allocation of MAC addresses and in response is allocated a block of addresses within the LEM 2 R address range. However, it is an important feature of the invention to depart from this basic request-and-allocation protocol with respect to MAC addresses for application exclusively within a LAN switch. For such applications, rather than allocating blocks of addresses within a LAN equipment manufacturer&#39;s dedicated address range, addresses from the shared ISR address range are used. 
   In a preferred assignment protocol, LAN equipment manufacturers assign MAC addresses to LAN switches. Thus, as shown, LEM 1   110  assigns LEM 1 R addresses to LEM 1  switch  115  which may be applied internally and externally. Similarly, LEM 2   120  assigns LEM 2 R addresses to LEM 2  switch  125  which may be applied internally and externally. However, in an important feature of the invention, LEM 1   110  and LEM 2   125  also assign ISR addresses to their respective switches  115  and  125  solely for internal application. The ISR addresses assigned by LEM 1   110  and LEM 2   120  to their respective switches  115  and  125  are from the shared ISR address range within MAC address domain  100  and, therefore, may (but do not necessarily) include one or more identical addresses. 
   In a preferred assignment protocol, LAN equipment manufacturers assign MAC addresses to LAN switches. Thus, as shown, LEM 1   110  assigns LEM 1 R addresses to LEM  1  switch  1115  which may be applied internally and externally. Similarly, LEM 2   120  assigns LEM 2 R addresses to LEM 2  switch  125  which may  5  be applied internally and externally. However, in an important feature of the invention, LEM  1   110  and LEM 2   120  also assign ISR addresses to their respective switches  115  and  125  solely for internal application. The ISR addresses assigned by LEM 1   110  and LEM 2  120 to their respective switches  115  and  125  are from the shared ISR address range within MAC address domain  10   100  and, therefore, may (but do not necessarily) include one or more identical addresses. 
   Various elaborations of the reservation, request, allocation, assignment and application protocols heretofore described are possible, as described hereinafter. Nevertheless, at a fundamental level, these basic protocols, despite their apparent simplicity, are believed to confer significant advances over the prior art. 
   Referring now to  FIG. 2 , a LAN switch in which MAC addresses allocated in accordance with a preferred embodiment of the invention may be assigned and applied is shown. Switch  200  includes a matrix of frame buses  211 - 219  driven by interfaces  201 - 209 , respectively. Interfaces  201 - 209  include network interfaces  201 - 208  connected to respective LANs  221 - 228  via respective transmission media  231 - 238 , and management interface  209 . Each bus has a root interfacing with the one of interfaces  201 - 209  having the exclusive right to transmit frame data on the bus (i.e. the root interface) and leaves interfacing with the plurality of interfaces  201 - 209  receiving frame data off the bus (i.e. the leaf interfaces). Preferably, each interface is the root interface on one of buses  211 - 219  and is a leaf interface on all buses  211 - 219 , including the bus for which it is the root interface. Buses  211 - 219  are broadcast-oriented such that all data bursts propagated on a bus reach all interfaces  201 - 209 . In addition to transmitting and receiving frame data, management interface  209  serves as the “nerve center” of switch  200  which assists network interfaces  201 - 208  in special frame processing, including processing of Spanning Tree frames as hereinafter described. Of course, the root-to-leaf architecture described above is one of many possible architectures for a switch operative in accordance with the present invention. 
   Other architectures may have a single common bus between interfaces or “full mesh” matrix providing point-to-point connections between all combinations of interfaces. 
   Interfaces  201 - 209  perform filtering checks on frames received of buses  211 - 219  by looking at MAC addresses in a local header appended to frames. Frames not having as a MAC address an address known by interfaces  201 - 209  are dropped, or “filtered”, subject to certain exceptions. One exception applies when none of interfaces  201 - 209  recognizes the MAC address. Interfaces  201 - 209  share the results of filtering checks to avoid filtering frames whose MAC address has not been learned by any interface. Such “unknown destination” frames are captured by all interfaces. More particularly, in an exemplary filtering check, an interface applies the following filtering rules:
         Rule 1: If the frame has a MAC address known on the interface, the filtering check is passed. The frame is captured.   Rule 2: If the frame has a MAC address not known on the interface, and the MAC address is known on another interface, the filtering check is failed. The frame is filtered.   Rule 3: If the frame has a MAC address not known on the interface, and the MAC address not known on another interface, the filtering check is passed. The frame is captured.
 
A frame in this context may be any protocol data unit having a MAC header with a destination MAC address therein. A frame may in certain circumstances encapsulate an entire Network layer protocol data unit (e.g. an entire IP packet). By way of example, frames may be Ethernet protocol data units and Spanning Tree protocol data units.
       

   An exemplary application of conventional and exceptional frame forwarding will now be described by reference to frames traversing switch  200 . In  FIGS. 3 through 5 , an exemplary application of conventional frame forwarding, which does not apply an ISR address, is illustrated. Frame  300 , originated by an end-station on a LAN associated with one of network interfaces  201 - 208  and destined for an end-station on a LAN associated with a different one of network interfaces  201 - 208  arrives at switch  200 . Frame  300  includes a MAC header, an 802.1Q tag, an IP header and additional information not relevant to the present example. The MAC header includes, among other information not shown, a destination MAC address of the destination end-station; in this case a globally unique address allocated to LAN equipment manufacturer X (LEMXR 1 ). The network interface receiving frame  300  from the LAN appends a local header to frame  300  which includes the MAC address LEMXR 1  retrieved from the MAC header, resulting in frame  400 . Frame  400  is propagated on the one of buses  211 - 218  for which the receiving network interface is the root interface. Frame  400  is received from the one of buses  211 - 218  by all interfaces  201 - 209 , which perform filtering checks individually by looking at the MAC address in the local header. The MAC address LEMXR 1  is known on the network interface through which the destination end-station is connected to switch  200  (generally as a result of a “source learning’ operation performed on a previous frame transmitted by the destination end-station), therefore filtering Rule 1 (above) applies and the frame is captured by such interface. The MAC address LEMXR 1  is not known on the other network interfaces or management interface  209 , therefore filtering Rule 2 (above) applies and the frame is filtered by such interfaces. The capturing network interface strips the local header from the frame, resulting in frame  500 , which is forwarded out the capturing network interface to the destination end-station. 
   In  FIGS. 6 through 9 , an exemplary application of exceptional frame forwarding, which applies an ISR address ISR 1 , is illustrated. In the exemplary application, the exceptional forwarding enables dynamic path selection. Frame  600  includes a MAC header and additional information not relevant to the present example. The MAC header includes, among other information, a destination MAC address; in this case a dynamic path selection address (DPS 1 ). The network interface receiving frame  600  applies a local header to frame  600  which includes the MAC address DPS 1  retrieved from the MAC header resulting in frame  700 . Frame  700  is propagated on the one of buses  211 - 218  for which the receiving network interface is the root interface. Frame  700  is received from the one of buses  211 - 218  by all interfaces  201 - 209 , which perform individual filtering checks by looking at the MAC address in the local header. The MAC address DPS 1  is known on management interface  209 , which has been configured to recognize the address. Therefore filtering Rule 1 applies and frame  700  is captured by management interface  209 . The MAC address DPS 1  is not known on network interfaces  201 - 208 , however. Therefore filtering Rule 2 applies and frame  700  is filtered by network interfaces  201 - 208 . Management interface  209  resolves, based on the current state of a dynamic path selection algorithm, on which one of network interfaces  201 - 208  the frame must be forwarded by switch  200  and generates a frame  800  having a local header including “intra-switch only” MAC address ISR 1 , which the resolved forwarding network interface has been preconfigured to recognize. The destination MAC address in the MAC header remains DPS 1 . Frame  800  is propagated, on the backplane, this time on bus  219  for which management interface  209  is the root interface. Frame  800  is received by all interfaces  201 - 209 , which perform individual filtering checks by looking at the MAC address in the local header. The MAC address ISR, is known on the resolved forwarding network interface; therefore, filtering Rule 1 applies and the frame is captured by such interface. The MAC address ISR 1  is not known on the other network interfaces or management interface  209 ; therefore filtering Rule 2 applies and the frame is filtered by such interfaces. The resolved network interface strips the local header from frame  800  resulting in frame  900 , which is forwarded out the resolved network interface. In the foregoing manner, an “intra-switch only” MAC address is advantageously applied to effectuate dynamic path selection, resulting in conservation of a globally unique MAC address which would otherwise be used. It will be appreciated that each network interface may be configured to recognize a different “intra-switch only” MAC address such that multiple globally unique MAC addresses are conserved. 
   Turning now to  FIG. 10 , a flow diagram illustrating preferred reservation, request and allocation protocols for MAC addresses is presented. Separate and distinct MAC address ranges are reserved for LAN equipment manufacturer X (LEMXR) and for “intra-switch only” applications (ISR) ( 1010 ). A request for allocation of MAC addresses from a LAN equipment manufacturer X is received ( 1020 ), in response to which the LAN equipment manufacturer is allocated a block of addresses from its reserved address range (LEMXR addresses) ( 1030 ). 
   Turning finally to  FIG. 11 , a flow diagram illustrating preferred of assignment and application protocols for MAC addresses is presented. LAN equipment manufacturer X assigns MAC addresses to a LAN switch, including (i) for internal and external application, allocated MAC addresses reserved for LAN equipment manufacturer X (LEMXR addresses), and (ii) for “internal use only”, MAC addresses reserved for “intra-switch only” applications (ISR addresses) ( 1110 ). The switch is interconnected in a network ( 1120 ) and booted-up ( 1130 ). In network operation, LEMXR addresses are applied internally and externally, whereas ISR addresses are applied exclusively within the switch ( 1140 ). 
   It will be appreciated by those of ordinary skill in the art that the invention can be embodied in other specific forms without departing from the spirit or essential character hereof. The present description is therefore considered in all respects illustrative and not restrictive. The scope of the invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.