Abstract:
A bridge (EthOAM device) and method are described herein where the bridge implements the method and reduces a number of static entries (pre-defined multicast MAC addresses) which need to be configured within a database (e.g., forwarding database (FDB)) to support the flow of Ethernet OAM multicast frames such as, for example, Connectivity Check (CC) frames and Link Trace (LT) frames which are used in accordance with the IEEE 802.1ag standard.

Description:
CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/870,869 filed on Dec. 20, 2006 and entitled “Optimization of Memory for EthOAM Multicast Entries”. The contents of this document are hereby incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is related to a bridge and method for reducing a number of static entries which need to be configured within a database to support the flow of Ethernet OAM multicast frames such as, for example, Connectivity Check (CC) frames and Link Trace (LT) frames which are used in accordance with the IEEE 802.1ag standard. 
       BACKGROUND 
       [0003]    The following abbreviations are herewith defined, at least some of which are referred to in the ensuing description of the prior art and the present invention. 
       CC Continuity Check 
     CFM Connectivity Fault Management 
     DSAP Domain Service Access Point 
     FDB Forwarding Database 
     IEEE Institute of Electrical and Electronics Engineers 
     MA Maintenance Association 
     MAC Media Access Control 
     MD Maintenance Domain 
     MEP Maintenance End Point 
     MHF MIP Half Function 
     MIB Management Information Base 
     MIP Maintenance Intermediate Point 
     MP Maintenance Point 
     LT Link Trace 
     LTR Link Trace Reply 
     OAM Operation, Administration and Maintenance 
     PDB Permanent Database 
     PDU Protocol Data Unit 
     RAM Random Access Memory 
     SNMP Small Network Management Protocol 
     VLAN Virtual Local Area Network 
       [0004]    Referring to  FIG. 1  (PRIOR ART), there is a block diagram of a traditional bridge  100  which implements an IEEE 802.1ag standard that is used to help explain a problem with needing to configure a large number of static entries within a permanent database for pre-defined multicast MAC addresses associated with CC multicast frames and LT multicast frames. The traditional bridge  100  by implementing the IEEE 802.1ag standard is able to provide a connectivity fault management which is useful for detecting, isolating and reporting connectivity faults within Ethernet networks. The IEEE 802.1ag standard is well known to those skilled in the art but to aid in the understanding of the present discussion several of the key terms which are used herein and their definitions are provided below: 
         [0005]    CC message: A multicast CFM PDU transmitted periodically by a MEP to assure the continuity over the MA to which the transmitting MEP belongs. No reply is sent by any MP in response to receiving a CCM. 
         [0006]    Customer: A consumer of an Ethernet Service. The customer might lease a point to point or multipoint connection to a network provider. The customer is the final user of the Ethernet service. 
         [0007]    LT message: A CFM PDU initiated by a MEP to trace a path to a target MAC address, forwarded from MIP to MIP, up to the point at which the LTM reaches its target, a MEP, or can no longer be forwarded. Each MP along the path to the target generates an LTR. 
         [0008]    MA: A set of MEPs, each configured with the same MAID and MD Level, established to verify the integrity of a single service instance. An MA can also be thought of as a full mesh of Maintenance Entities among a set of MEPs so configured. 
         [0009]    MEP: An actively managed CFM entity, associated with a specific DSAP of a service instance, which can generate and receive CFM PDUs and track any responses. It is an end point of a single MA, and is an endpoint of a separate Maintenance Entity for each of the other MEPs in the same MA. 
         [0010]    MIP: A CFM entity consisting of two MHFs. MIPs are not actively monitored and are configured at intermediate points in the Ethernet service instance. 
         [0011]    Operator: An operator owns equipment used to create L2 or L3 networks. The operator can lease a subset of its network to providers. The operator (network operator) can, in fact, be identical to, or a part of the same organization as, the service provider, but for purposes of this discussion, the operator and service provider are presumed to be separate organizations. 
         [0012]    Provider: A provider does not actually own all its equipment but can manage limited functionalities of its Ethernet services leased to an operator. The provider can also act as a provider if it owns and is willing to lease Ethernet services. 
         [0013]    Owner: An owner of a system (and in particular, a Bridge) is a user who has full access to the System Group of the SNMPv2-MIB. 
         [0014]    For a more detailed discussion about the IEEE 802.1ag standard, reference is made to the current IEEE 802.1ag/D8 standard entitled “Local and Metropolitan Area Networks-Virtual Bridged Local Area Networks-Amendment 5: Connectivity Fault Management” dated Feb. 8, 2007. The contents of this document are hereby incorporated by reference herein. 
         [0015]    The traditional bridge  100  has a processor  102  that supports the flow of multicast frames such as CC and LT multicast frames and terminate the CC and LT multicast frames because it has previously configured pre-defined multicast MAC addresses which correspond to the CC and LT multicast frames at the appropriate level as permanent static entries within a filtering database  104  (FDB  104 ). The region within the FDB  104  that is occupied by the static entries is called the permanent database  106  (PDB  106 ). The traditional bridge  100  pursuant to the IEEE 802.1ag standard can support upto 4094 VLANs and eight levels where the eight levels are organized as follows: (1) customers can be assigned levels 7 or 6; (2) providers can be assigned levels 5, 4 and 3; and (3) operators can be assigned levels 2, 1 and 0 (see the aforementioned definitions of the customers, providers and operators). 
         [0016]    Plus, the traditional bridge  100  pursuant to the IEEE 802.1ag standard reserves upto eight multicast MAC addresses for CC multicast frames (one for each level) and upto eight multicast MAC addresses for LT multicast frames (one for each level). The eight multicast MAC addresses for the CC multicast frames and the eight multicast MAC addresses for the LT multicast frames are all pre-defined/reserved in the current IEEE 802.1ag standard as follows: 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 01-80-C2-xx-xx-xy 
               
             
          
           
               
                   
                 MD Level of CC message 
                 Four address bits “y” 
               
               
                   
                   
               
               
                   
                 7 
                 7 
               
               
                   
                 6 
                 6 
               
               
                   
                 5 
                 5 
               
               
                   
                 4 
                 4 
               
               
                   
                 3 
                 3 
               
               
                   
                 2 
                 2 
               
               
                   
                 1 
                 1 
               
               
                   
                 0 
                 0 
               
               
                   
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 01-80-C2-xx-xx-xy 
               
             
          
           
               
                   
                 MD Level of LT message 
                 Four address bits “y” 
               
               
                   
                   
               
               
                   
                 7 
                 F 
               
               
                   
                 6 
                 E 
               
               
                   
                 5 
                 D 
               
               
                   
                 4 
                 C 
               
               
                   
                 3 
                 B 
               
               
                   
                 2 
                 A 
               
               
                   
                 1 
                 9 
               
               
                   
                 0 
                 8 
               
               
                   
                   
               
             
          
         
       
     
         [0017]    In operation, the traditional bridge  100  upon receiving a CC multicast frame or LT multicast frame takes their destination multicast MAC address and performs a table look-up operation in the PDB  106  and if there is a previously stored static entry with the same multicast MAC address then the received CC multicast frame or LT multicast frame is terminated and further processed within the bridge&#39;s software (note: the level of the received CC multicast frame or the LT multicast frame is encoded in the last four bits of the multicast MAC address). 
         [0018]    However, the traditional bridge  100  by needing to support upto 4094 VLANs and upto eight levels for both CC and LT multicast frames means that the number of static entries that may need to be configured in the PDB  106  so as to store the CC and LT reserved multicast MAC addresses can be as high as (4094×8)×2=655504. Unfortunately, most traditional bridges  100  do not have enough space to support and store such a large number of static entries within their PDB  106 . An example is provided next to help illustrate how the traditional bridge  100  needs to configure the static entries within the PDB  106  for both the CC and LT reserved multicast MAC addresses for each supported VLAN. In this example, assume the traditional bridge  100  supports five maintenance associations (MAs) as follows: 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
             
             
               
                 MA1 
                 VLAN 100 
                 Level 5 
               
               
                 MA2 
                 VLAN 50 
                 Level 5 
               
               
                 MA3 
                 VLAN 40 
                 Level 4 
               
               
                 MA4 
                 VLAN 30 
                 Level 3 
               
               
                   
               
             
          
         
       
     
         [0019]    To configure MA1 which is associated with VLAN 100 at level 5, the traditional bridge  100  (e.g., traditional MEP  100 ) would create six static entries within the PDB  106  for the reserved CC multicast MAC addresses associated with levels 5 through 0 and also create six static entries within the PDB  106  for the reserved LT multicast MAC addresses associated with levels 5 through 0. These twelve static entries are illustrated as elements 1-12 within TABLE 3. 
         [0020]    To configure MA2 which is associated with VLAN 50 at level 5, the traditional bridge  100  (e.g., traditional MEP  100 ) would create six static entries within the PDB  106  for the reserved CC multicast MAC addresses associated with levels 5 through 0 and also create six static entries within the PDB  106  for the reserved LT multicast MAC addresses associated with levels 5 through 0. These twelve static entries are illustrated as elements 13-24 within TABLE 3. 
         [0021]    To configure MA3 which is associated with VLAN 40 at level 4, the traditional bridge  100  (e.g., traditional MEP  100 ) would create five static entries within the PDB  106  for the reserved CC multicast MAC addresses associated with levels 4 through 0 and also create five static entries within the PDB  106  for the reserved LT multicast MAC addresses associated with levels 4 through 0. These ten static entries are illustrated as elements 25-34 within TABLE 3. 
         [0022]    To configure MA4 which is associated with VLAN 30 at level 3, the traditional bridge  100  (e.g., traditional MEP  100 ) would create four static entries within the PDB  106  for the reserved CC multicast MAC addresses associated with levels 3 through 0 and also create four static entries within the PDB  106  for the reserved LT multicast MAC addresses associated with levels 3 through 0. These eight static entries are illustrated as elements 35-52 within TABLE 3. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Static 
                   
                   
               
               
                 Entry 
                 Vlan ID 
                 Multicast MAC Address 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 100 
                 CC 5 
               
               
                 2 
                 100 
                 CC 4 
               
               
                 3 
                 100 
                 CC 3 
               
               
                 4 
                 100 
                 CC 2 
               
               
                 5 
                 100 
                 CC 1 
               
               
                 6 
                 100 
                 CC 0 
               
               
                 7 
                 100 
                 LT 5 
               
               
                 8 
                 100 
                 LT 4 
               
               
                 9 
                 100 
                 LT 3 
               
               
                 10 
                 100 
                 LT 2 
               
               
                 11 
                 100 
                 LT 1 
               
               
                 12 
                 100 
                 LT 0 
               
               
                 13 
                 50 
                 CC 5 
               
               
                 14 
                 50 
                 CC 4 
               
               
                 15 
                 50 
                 CC 3 
               
               
                 16 
                 50 
                 CC 2 
               
               
                 17 
                 50 
                 CC 1 
               
               
                 18 
                 50 
                 CC 0 
               
               
                 19 
                 50 
                 LT 5 
               
               
                 20 
                 50 
                 LT 4 
               
               
                 21 
                 50 
                 LT 3 
               
               
                 22 
                 50 
                 LT 2 
               
               
                 23 
                 50 
                 LT 1 
               
               
                 24 
                 50 
                 LT 0 
               
               
                 25 
                 40 
                 CC 4 
               
               
                 26 
                 40 
                 CC 3 
               
               
                 27 
                 40 
                 CC 2 
               
               
                 28 
                 40 
                 CC 1 
               
               
                 29 
                 40 
                 CC 0 
               
               
                 30 
                 40 
                 LT 4 
               
               
                 31 
                 40 
                 LT 3 
               
               
                 32 
                 40 
                 LT 2 
               
               
                 33 
                 40 
                 LT 1 
               
               
                 34 
                 40 
                 LT 0 
               
               
                 35 
                 30 
                 CC 3 
               
               
                 36 
                 30 
                 CC 2 
               
               
                 37 
                 30 
                 CC 1 
               
               
                 38 
                 30 
                 CC 0 
               
               
                 39 
                 30 
                 LT 3 
               
               
                 40 
                 30 
                 LT 2 
               
               
                 41 
                 30 
                 LT 1 
               
               
                 42 
                 30 
                 LT 0 
               
               
                   
               
               
                 Note: 
               
               
                 CCx: Reserved multicast MAC address for CC for level x. 
               
               
                 LTx: Reserved multicast MAC address for LT for level x. 
               
             
          
         
       
     
         [0023]    Accordingly, there has been and is a need to provide a solution which can be implemented by a bridge to reduce the number of static entries that need to be configured in the PDB  106  while still being able to support 4094 VLANs and 8 Levels. This need and other needs are satisfied by the present invention. 
       SUMMARY 
       [0024]    In one aspect, the present invention provides a method for reducing a number of static entries which need to be configured within a database of a bridge. The method includes the steps of: (1) forming one or more VLAN sets where each VLAN set contains one or more VLAN(s) that are configured at a same level; (2) creating a list of supported levels; (3) configuring a static entry within the database for each reserved multicast address for a lowest supported level and all lesser levels through zero which correspond with the VLAN(s) in the VLAN set at the lowest supported level; (4) removing a current lowest supported level from the list of supported levels; (5) configuring a static entry within the database for each reserved multicast address for the current lowest supported level through a highest level so far configured plus one which correspond with the VLAN(s) in the VLAN set at the current lowest supported level; and (6) repeating the removing step (4) and the second configuring step (5) until the list of supported levels is empty. 
         [0025]    In yet another aspect, the present invention provides a bridge (e.g., EthOAM entity) with a processor and memory with instructions stored therein which are processable by the processor to reduce a number of static entries that need to be stored within a database by: (1) forming one or more VLAN sets where each VLAN set contains one or more VLAN(s) that are configured at a same level; (2) creating a list of supported levels; (3) configuring a static entry within the database for each reserved multicast address for a lowest supported level and all lesser levels through zero which correspond with the VLAN(s) in the VLAN set at the lowest supported level; (4) removing a current lowest supported level from the list of supported levels; (5) configuring a static entry within the database for each reserved multicast address for the current lowest supported level through a highest level so far configured plus one which correspond with the VLAN(s) in the VLAN set at the current lowest supported level; and (6) repeating the removing step ( 4 ) and the second configuring step ( 5 ) until the list of supported levels is empty. 
         [0026]    Additional aspects of the invention will be set forth, in part, in the detailed description, figures and any claims which follow, and in part will be derived from the detailed description, or can be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    A more complete understanding of the present invention may be obtained by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein: 
           [0028]      FIG. 1  (PRIOR ART) is a block diagram illustrating the basic components of a traditional bridge which is used to help explain a problem with needing to configure a large number of static entries within a database that is addressed by the present invention; 
           [0029]      FIG. 2  is a block diagram illustrating the basic components of a bridge which has been configured to reduce the number of static entries that need to be configured within a database in accordance with the present invention; and 
           [0030]      FIG. 3  is a flowchart illustrating the basic steps of a method for reducing the number of static entries that need to be configured within the database of a bridge in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    Referring to  FIGS. 2 and 3 , there are respectively shown a block diagram of a bridge  200  and a flowchart of a method  300  that is implemented by the bridge  200  to reduce the number of static entries which need to be configured in a FDB  202  (in particular a PDB  204 ) in accordance with the present invention. In particular, the bridge  200  has a memory  206  (e.g., RAM memory  206 ) which stores instructions that are processable by a processor  208  to facilitate the various steps of the memory optimization method  300  as follows: 
         [0000]    Step 1: Form one or more VLAN sets (e.g., Vx, Vy, Vz) where each VLAN set contains one or more VLAN(s) that are configured at a same level (see step  302  in  FIG. 3 ). In particular, the VLANs that are at the same level can be grouped into a VLAN set as follows: 
       Vx={Vx1, Vx2, . . . , Vxn} where Vx=VLANs configured for level x 
     Vy={Vy1, Vy2, . . . , Vyn} where Vy=VLANs configured for level y 
     Vz={Vz1, Vz2, . . . , Vzn} where Vz=VLANs configured for level z where x&gt;y&gt;z. 
     Step 2: Create a list of the levels supported by the bridge  200  and find the smallest level in this list (z) (see step  304  in FIG. 3). 
       [0032]    Step 3: Configure a static entry within the PDB  204  for each pre-defined/reserved CC and LT multicast MAC address for the lowest supported level (z) and all lesser levels through zero which correspond with the VLAN(s) in the VLAN set at the lowest level (z) (see step  306  in  FIG. 3 ). 
       Step 4: Remove the current lowest level from the list of supported levels (see step  308  in FIG. 3). 
       [0033]    Step 5: Configure a static entry within the PDB  204  for each pre-defined/reserved CC and LT multicast MAC address at the current lowest supported level through a highest level so far configured plus one which correspond with the VLAN(s) in the VLAN set at the current lowest supported level (see step  310  in  FIG. 3 ). 
       Step 6. Repeat Steps 4 and 5 until the list of supported levels is empty (see steps  312  and  314  in FIG. 3). 
       [0034]    A graphical result of this optimization is shown below in TABLE 4. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                   
                 MAC Addresses to be 
                 Number of Multicast 
               
               
                 VLAN set 
                 Configured 
                 Entries 
               
               
                   
               
             
             
               
                 {Vx, VY, Vz} 
                 CCz, CCz-1, . . . , CC0 
                 2 (z + 1) 
               
               
                   
                 LTz, LTz-1, . . . , LT0 
               
               
                 {Vx, Vy} 
                 CCy, CCy-1 . . . CCy-(y-z-1) 
                 2 (y − z) 
               
               
                   
                 LTy, LTy-1 . . . LTy-(y-z-1) 
               
               
                 {Vx} 
                 CCx, CCx-1, . . . , CCx- 
                 2 (x − y) 
               
               
                   
                 (x-y-1) 
               
               
                   
                 LTx, LTx-1, . . . , LTx- 
               
               
                   
                 (x-y-1) 
               
               
                   
               
             
          
         
       
     
         [0035]    This table should be read as follows: For the first row, these MAC addresses (CCz, CCz−1, . . . , CC0 and LTz, LTz−1, . . . , LT0) need to be configured in PDB  204  for VLAN set {Vx, Vy, Vz}. In the second row, these MAC addresses (CCy, CCy−1, . . . , CCy−(y−Z−1) and LTy, LTy−1, . . . , LTy−(y−Z−1)) need to be configured in PDB  204  for VLAN set {Vx, Vy}. In the third row, these MAC addresses (CCx, CCx−1, . . . , CCx−(x−y−1) and LTx, LTx−1, . . . , LTx−(x−y−1)) need to be configured in PDB  204  for VLAN set {Vx}. 
         [0036]    As can be seen, the present invention is a marked improvement over the prior art since the total number of static entries that need to be configured in memory with optimization=2 (z+1+y−z+x−y)=2x+2. While, the total number of static entries that need to be configured in memory without optimization=[(2*#of VLANs at level z*(z+1))+(2*#of VLANs at level y*(y+1))+(2*#of VLANs at level z*(x+1))]. This savings is illustrated below by using the same example that was discussed above with respect to the prior art but now the memory optimization method  300  of the present invention is used to configure the static entries in the PDB  204  of the bridge  200 . 
         [0037]    In this example, assume the bridge  200  supports five maintenance associations (MAs) as follows: 
         [0000]                                        MA1   VLAN 100   Level 5       MA2   VLAN 50   Level 5       MA3   VLAN 40   Level 4       MA4   VLAN 30   Level 3                    
Step 1: Group the VLANs that are at the same level as follows:
 
         [0038]    V5={VLAN100, VLAN50} 
         [0039]    V4={VLAN40} 
         [0040]    V3={VLAN30} 
         [0041]    where Vx: is the Vlan at level x (see step  302  in  FIG. 3 ). 
       Step 2: Create a list of the supported levels {5,4,3} and find the smallest level {3} in this list (see step  304  in FIG. 3). 
       [0042]    Step 3: Configure a static entry within the PDB  204  for each pre-defined/reserved CC and LT multicast MAC address for the lowest supported level {3} and all lesser levels through zero which correspond with the VLAN(s) in the VLAN set V3 (note: the eight configured static entries are illustrated as elements 1-8 in TABLE 4) (see step  306  in  FIG. 3 ).
 
Step 4: Remove the current lowest level {3} from the list of supported levels. Thus, the smallest level now in the list is level {4} (see step  308  in  FIG. 3 ).
 
Step 5: Configure a static entry within the PDB  204  for each pre-defined/reserved CC and LT multicast MAC address at the current lowest supported level {4} through a highest level so far configured plus one {3+1} which correspond with the VLAN(s) in the VLAN set V4 (note: the two configured static entries are illustrated as elements 9-10 in TABLE 4) (see step  310  in  FIG. 3 ).
 
Step 6A (repeat step 4): Remove the current lowest level {4} from the list of supported levels. Thus, the smallest level now in the list is level {5} (see step  312  and step  308  (second time) in  FIG. 3 ).
 
Step 6B (repeat step 5): Configure a static entry within the PDB  204  for each pre-defined/reserved CC and LT multicast MAC address at the current lowest supported level {5} through a highest level so far configured plus one {4+1} which correspond with the VLAN(s) in the VLAN set V5 (note: the two configured static entries are illustrated as elements 11-12 in TABLE 4) (see step  310  (second time) in  FIG. 3 ).
 
       Step 7: The memory optimization method  300  is stopped since the list of levels is now empty (see step  314  in FIG. 3). 
       [0043]    The results of performing steps 1-7 for this particular example are illustrated in TABLES 5 and 6: 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Static 
                   
                   
               
               
                 Entry 
                 VLAN Set 
                 Multicast MAC Address 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 {100, 50, 40, 30} 
                 CC 3 
               
               
                 2 
                 {100, 50, 40, 30} 
                 CC 2 
               
               
                 3 
                 {100, 50, 40, 30} 
                 CC 1 
               
               
                 4 
                 {100, 50, 40, 30} 
                 CC 0 
               
               
                 5 
                 {100, 50, 40, 30} 
                 LT 3 
               
               
                 6 
                 {100, 50, 40, 30} 
                 LT 2 
               
               
                 7 
                 {100, 50, 40, 30} 
                 LT 1 
               
               
                 8 
                 {100, 50, 40, 30} 
                 LT 0 
               
               
                 9 
                 {100, 50, 40} 
                 CC 4 
               
               
                 10 
                 {100, 50, 40} 
                 LT 4 
               
               
                 11 
                 {100, 50} 
                 CC 5 
               
               
                 12 
                 {100, 50} 
                 LT 5 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                 MAC Addresses to 
                 Number of multicast 
               
               
                   
                 VLAN set 
                 be Configured 
                 entries 
               
               
                   
                   
               
             
             
               
                   
                 (V5, V4, V3) 
                 CC3, CC2, CC1, CC0 
                 8 
               
               
                   
                   
                 LT3, LT2, LT1, LT0 
               
               
                   
                 (V5, V4) 
                 CC4, LT4 
                 2 
               
               
                   
                 (V5) 
                 CC5, LT5 
                 2 
               
               
                   
                   
               
             
          
         
       
     
         [0044]    As can be seen in TABLES 5 and 6, the total number of static entries configured in the PDB  204  is 12 (elements 1-12). In contrast, in the prior art example 42 static entries had to be configured in the PDB  106  as shown in TABLE 3. Thus, the number of configured static entries has been reduced by 42−12=30. In this particular example, this results in memory savings of 75%. 
         [0045]    From the foregoing, it can be readily appreciated by those skilled in the art that the present invention provides a memory optimization method  300  that reduces the amount of memory needed to store the static entries that are associated with EthOAM by: (1) identifying groups of VLANs that are at the same level; and (2) storing them all in one entry as follows: &lt;VLAN x, VLAN y, VLAN p, reserved MAC address G&gt;. This is done for every group of VLAN, starting from the lowest level. In contrast, in the prior art a separate entry needed to be stored for each VLAN as follows: &lt;VLAN x, MAC G&gt;, &lt;VLAN y, MAC G&gt;, &lt;VLAN p, MAC G&gt;. The memory optimization method  300  can be implemented in any bridge  200  that has a microprocessor RAM which can store entries in the format &lt;VLANx, VLANy, VLANZ, MAC&gt;. Thus, the bridge  200  after configuring the static entries in the PDB  204  can receive an incoming frame and perform the following operations: (1) determine the VLAN (there is no need to know the level); (2) look-up the PDB  204  and check if the destination MAC address in the incoming frame matches any of the stored multicast MAC destination addresses; and (3) if there is a match then terminate the incoming frame. 
         [0046]    Although one embodiment of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.