Abstract:
A switch and a method are described herein that are capable of performing the following steps: (a) receiving the unicast packet which is a L3 routed packet at a port in a first Virtual Local Area Network (VLAN); (b) routing the received packet to a loopback port in a second VLAN; (c) receiving the routed packet which is now a L2 multicast packet from the loopback port in the second VLAN; and (d) bridging the routed packet to multiple ports in the second VLAN.

Description:
CLAIMING BENEFIT OF PRIOR FILED U.S. APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 60/869,164 filed on Dec. 8, 2006 and entitled “Multicasting Unicast Traffic/Multiple Classification of a Packet”. The contents of this document are hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a switch that receives a unicast packet (which has a routed Media Access Control (MAC) address) in a first Virtual Local Area Network (VLAN) and then multicasts/floods/bridges copies of the packet (after it has been modified to have a multicast MAC address) from a second VLAN. 
     BACKGROUND 
     The following abbreviations are herewith defined, at least some of which are referred to in the following description associated with the prior art and the present invention. 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 ARP 
                 Address Resolution Protocol 
               
               
                   
                 CLI 
                 Command Line Interface 
               
               
                   
                 CPU 
                 Central Processing Unit 
               
               
                   
                 ECMP 
                 Equal Cost Multi-Path 
               
               
                   
                 IP 
                 Internet Protocol 
               
               
                   
                 LPM 
                 Lowest Prefix Match 
               
               
                   
                 MAC 
                 Media Access Control 
               
               
                   
                 NI 
                 Network Interface Card 
               
               
                   
                 SA 
                 Source Address 
               
               
                   
                 TTL 
                 Time to Live 
               
               
                   
                 VLAN 
                 Virtual Local Area Network 
               
               
                   
                   
               
             
          
         
       
     
     It would be desirable to have a switch that can receive a unicast packet (which has a router MAC address) in a first VLAN and then multicast/flood copies of that packet from a second VLAN. The ability to multicast a unicast packet (e.g., traffic, data stream) in this manner would be desirable in a wide variety of applications including, for example, server farms and redundant firewalls. In the first case, it would be desirable if a user can have their switch multicast the received unicast packet to multiple servers because each of the servers need to receive a redundant backup of the unicast packet. In the second case, it would be desirable if a user can have their switch multicast the received unicast packet to redundant firewalls because each of the firewalls need to receive the same packets so that they can provide the necessary redundancy. 
     The traditional switches cannot receive unicast packets at one VLAN and then multicast the packets at a second VLAN because: (1) the packet is routed; (2) the packet does not have a broadcast MAC address as the destination MAC address; (3) the packet does not have a multicast MAC address as the destination MAC address; and (4) the packet does not have a multicast IP address as the destination IP address. Accordingly, there has been and is a need to address this particular shortcoming and other shortcomings which are associated with the traditional switches. This need and other needs are satisfied by the present invention. 
     SUMMARY 
     In one aspect, the present invention provides a switch and method for multicasting a unicast packet by: (a) receiving the unicast packet which is a L3 routed packet at a port in a first VLAN; (b) routing the received packet to a loopback port in a second VLAN; (c) receiving the routed packet which is now a L2 multicast packet from the loopback port in the second VLAN; and (d) bridging the routed packet to multiple ports in the second VLAN. 
     In another aspect, the present invention provides a switch and method for multicasting a unicast packet by receiving the unicast packet which is a L3 routed packet at a port in a first VLAN. Then, the switch and method route the received unicast packet to a loopback port in a second VLAN, where the routing operation further includes: (1) looking-up a destination MAC address of the received unicast packet within a L2 table and determining that the destination MAC address is a router MAC address; (2) looking-up a destination IP address of the received unicast packet within a L3 table and after a match is found modifying the received unicast packet as follows: (i) replacing the router MAC address with a multicast MAC address; (ii) modifying a VLAN tag from the first VLAN to the second VLAN; and (iii) decrementing a TTL value. Thereafter, the switch and method receive the routed packet which is now a L2 multicast packet from the loopback port in the second VLAN. Finally, the switch and method bridge the routed packet to multiple ports in the second VLAN, where the bridging operation further includes: (1) looking-up a destination MAC address of the received routed packet within the L2 table and determining that the destination MAC address is not present within the L2 table because the destination MAC address is a multicast MAC address; and (2) flooding copies of the routed packet to the multiple ports in the second VLAN. 
     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 
       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: 
         FIG. 1  is a block diagram illustrating the basic components of a switch that has been configured to multicast a received unicast packet in accordance with the present invention; 
         FIG. 2  is a flowchart illustrating the basic steps of a method for multicasting a unicast packet in accordance with the present invention; and 
         FIGS. 3A-3D  are diagrams which illustrate the different fields of a packet when it is received, routed and multicast by the switch in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , there are respectively shown a block diagram of a switch  100  and a flowchart of a method  200  that can be implemented by the switch  100  to multicast a unicast packet in accordance with the present invention (note: a packet is also considered to be traffic by those skilled in the art and as such the two terms may be used interchangeably herein). In operation, the switch  100  receives a unicast packet  102  (which has a router MAC address and is a L3 routed packet  102 ) at a front panel port  104  in a first VLAN A (see point  1  and step  202 ). The switch  100  has an ingress/forwarding logic unit  106  that routes the received packet  102 ′ (which has been modified to have a multicast MAC address) to a loopback port  108  (e.g., programmed to be in a PHY loopback mode) in a second VLAN D (see point  2  and step  204 ) (note: the loopback port  108  can occur in, for example, chip logic, PHY, MAC or even be externally cabled). Then, the switch  100  and in particular the ingress/forwarding logic unit  106  receives the routed packet  102 ′ (which is now a L2 multicast packet) from the loopback port  108  in the second VLAN D (see point  3  and step  206 ). Thereafter, the switch  100  and in particular the ingress/forwarding logic unit  106  multicasts/bridges/floods copies of the routed packet  102 ″ to multiple ports  110   a ,  110   b  . . .  110   n  in the second VLAN D (see point  4  and step  208 ). An exemplary scenario is described next to help further explain how the switch  100  by implementing method  200  can receive the unicast packet  102  (which has a router MAC address) in a first VLAN A and then multicast the received packet  102 ″ (after it has been routed and modified to have a multicast MAC address) from a second VLAN D in accordance with the present invention. 
     In the exemplary scenario, assume the switch  100  has a free port (e.g., port  108 ) which is then configured to be in a PHY loopback mode (via internal programming of software). In addition, the loopback port  108  is configured to be an 8021Q port and is tagged in all of the VLANs within the switch  100  (via internal programming of software) (note: an 8021Q port sends tagged packets which also indicate the originating VLAN A and the traversing VLAN D). Moreover, the switch  100  has a NI  112  which an operator can use a CLI to configure a L2 table  114  and a L3 table  116  located therein which makes it possible to implement the present invention (note: how these particular tables are used will be discussed in detail below). Assume the L2 table  114  (e.g., the L2_Entry_Table  114 ) is configured as follows: 
     
       
         
               
               
             
           
               
                   
                 L2 TABLE 
               
               
                   
                   
               
             
             
               
                   
                 L2 Entry 1   
               
               
                   
                 00:d0:95:81:bb:00 L3 = 1 
               
               
                   
                   
               
             
          
         
       
     
     And, assume the L3 table  116  (e.g., the L3_Entry_IPV4 Unicast_Table  116 , the L3 DEFIP_Table  116 , the EGR_L3_NEXT_HOP_Table  116 , the ING_L3_NEXT_HOP_Table  116  and the EGR_L3_INTF_Table  116 ) has entries which are configured as follows: 
     
       
         
               
             
           
               
                 L3 TABLE 2   
               
               
                   
               
             
             
               
                 L3_ENTRY_IPV4 UNICAST 
               
               
                 IP Addr. = IP D 128.251.40.22 
               
               
                 Next Hop Index = 1 
               
               
                 EGR_L3_NEXT_HOP 3   
               
               
                 MAC ADDRESS = 01:00:00:00:00:02 
               
               
                 INTF_NUM = 1 
               
               
                 ING_L3_NEXT_HOP 4   
               
               
                 MODULEID, PORT_TGID = Port L (26) 
               
               
                 EGR_L3_INTF 
               
               
                 MAC ADDRESS FOR SA replacement = Router MAC 
               
               
                 00:d0:95:81:bb:00 
               
               
                 VID = VLAN D 
               
               
                   
               
               
                 Note 1: 00:d0:95:81:bb:00 is the Destination MAC address (router MAC address) of incoming packet 102. 
               
               
                 Note 2: To populate the L3 table 116, the operator configures the ARP for IP address D using the CLI as follows: arp 128.251.40.22 01:00:00:00:00:02 (where IP D = 128.251.40.22 and multicast MAC = 01:00:00:00:00:02). 
               
               
                 Note 3: 01:00:00:00:00:02 is the multicast MAC address for the modified routed packet 102′. 
               
               
                 Note 4: The next hop port is identified as Port L (26) which is the loopback port 108. 
               
             
          
         
       
     
     At point  1 , the packet  102  (which is destined to IP address D) originally ingresses the switch  100  at port  104  in VLAN A (see  FIG. 1 ).  FIG. 3A  illustrates the relevant fields that are associated with an exemplary incoming packet  102  which include: (1) Destination MAC address (which is a Router MAC address); (2) SA MAC address; (3) VLAN tag (which is VLAN A); (4) IP Type; TTL (which is set at 64); (5) Src IP address (which is Src IP A); and (6) Dst IP address (which is Dst IP D). 
     At point  2 , the ingress/forwarding logic unit  106  takes the Destination MAC address (in this example 00:d0:95:81:bb:00) from packet  102  and looks-up the L2_Entry_Table  114 . The L2_Entry Table  114  has this Destination MAC address with the L3 bit set which indicates that this Destination MAC address is a router MAC address. As a result, the ingress/forwarding logic unit  106  forwards the packet  102  through the L3 Routing Process where the Dst IP address D (in this example 128.251.40.22) is looked-up in the L3_Entry_IPV4_Unicast_Table  116  or L3_DEFIP_Table  116 . A match is found for Dst IP address D in the L3 routing table, at which point, the ingress/forwarding logic unit  106  modifies the packet  102  and egresses the modified packet  102 ′ out the next hop port  108  (loopback port  108 ). The packet  102  is modified as follows: (1) replace the router MAC address (00:d0:95:81:bb:00) with a multicast MAC address (01:00:00:00:00:02) (see the EGR_L3_NEXT_HOP field in the L3 table  116 ); (2) change the VLAN tag from the VLAN A to VLAN D (see the EGR_L3_INTF field in the L3 table  116 ) (note: the router MAC address is needed in this field because whenever a packet is routed the source MAC address of the packet is changed to the MAC address of the current switch which routed the packet); and (3) decrement the TTL from 64 to 63.  FIG. 3B  illustrates the relevant fields that are associated with an exemplary modified incoming packet  102 ′ which include: (1) Destination MAC address (which is a multicast MAC address); (2) SA MAC address; (3) VLAN tag (which is VLAN D); (4) IP Type; TTL (which is set at 63); (5) Src IP address (which is Src IP A); and (6) Dst IP address (which is Dst IP D). 
     In point  2 , it should be appreciated that when a packet like incoming packet  102  is destined to the router MAC address, the packet  102  is determined to be routed. This implies that the destination of the packet  102  is not explicitly obtained from the packet  102  but from the routing L3 table  116  (e.g., L3_Entry_IPV4_Unicast_Table  116 , next hop table  116 , LPM table  116 ). The routing L3 table  116  is looked up by using the destination IP address within the packet  102 . If a match is found in the routing L3 table  116 , then the packet  102  is routed to the destination port  108  as indicated by the ING_L3_NEXT_HOP field in the L3 table  116 . When the packet  102  is routed, the packet  102  is modified so that its destination MAC address becomes the next hop MAC address (or the multicast MAC address). The VLAN tag of the packet  102  is also changed from the ingress VLAN A to the egress VLAN D. Plus, the TTL on the packet  102  is also decremented by one as required by ARP to prevent loops. The packet  102  is considered a L3 packet when it first ingresses the switch  100  and when it is routed it is still considered a L3 packet. 
     At point  3 , the routed packet  102 ′ has egressed out the loopback port  108  or if one looked at this from a different view point the routed packet  102 ′ has ingressed the switch  100  via the loopback port  108  (note: recall that loopback port  108  is also associated with VLAN D). The routed packet  102 ′ is now considered a L2 packet within the log of the switch  100 .  FIG. 3C  illustrates the relevant fields that are associated with an exemplary loopbacked packet  102 ′ which include: (1) Destination MAC address (which is a multicast MAC address); (2) SA MAC address (3) VLAN tag (which is VLAN D); (4) IP Type; TTL (which is set at 63); (5) Src IP address (which is Src IP A); and (6) Dst IP address (which is Dst IP D). As can be seen, the loopbacked packet  102 ′ is the same as the modified packet  102 ′ but the fact is that the packet  102 ′ has egressed the loopback port  108  at point  2  and again ingressed the loopback port  108  at point  3 . Thus, even though the contents of the modified packet  102 ′ and the loopbacked packet  102 ′ are the same, technically the loopbacked packet  102 ′ is a new packet and as such goes through the forwarding logic again as will be discussed in detail in the following paragraph. 
     At point  4 , the ingress/forwarding logic unit  106  takes the Destination MAC address (in this example 01:00:00:00:00:02) from the loopbacked packet  102 ′ and looks-up the L2_Entry_Table  114 . In this case, the Destination MAC address is a multicast MAC address which would not be present in the L2_Entry_Table  114 . As the destination MAC address is not present in the L2_Entry_Table  114  and the ingress/forwarding logic unit  106  is unable to determine the final destination, then the ingress/forwarding logic unit  106  floods copies of the loopbacked packet  102 ′ in Vlan D. Thus, ports  110   a ,  110   b  . . .  110   n  being members of VLAN D receive a copy of the loopbacked packet  102 ′ (which is now technically a bridged packet  102 ″).  FIG. 3D  illustrates the relevant fields that are associated with an exemplary bridged packet  102 ″ which include: (1) Destination MAC address (which is a multicast MAC address); (2) SA MAC address; (3) VLAN tag (which is VLAN D); (4) IP Type; TTL (which is set at 63); (5) Src IP address (which is Src IP A); and (6) Dst IP address (which is Dst IP D). At this point, the packet  102  has been routed once and bridged once within the switch  100  but the user perceives the packet  102  has having only been routed once by the switch  100 . 
     It should be appreciated that the destination MAC address does not need to be a multicast MAC address instead any MAC address which does not exist in the MAC table could be used. The multicast MAC address was used in this exemplary implementation so that the software can easily determine when to provide the desired multicasting behavior. Plus, if the MAC address is a L2 multicast MAC address then the L2 Multicast table  114  can be programmed to multicast the packet  102  out selective ports of the second VLAN D. In particular, if the MAC address is a L2 multicast MAC, then the L2MC_PTR can be programmed to point to an entry in the L2MC table. And, the PORT_BITMAP field in the L2MC table indicates the ports the packet is to be multicast out on and is referenced when the destination MAC is a MULTICAST MAC (note: flooding and multicasting are the same when the packet is sent to all of the ports in a VLAN but the term multicasting and not flooding is used to indicate the forwarding of the packet to selected ports in a VLAN). 
     The present invention has several different applications in which it could be used and two of those applications are as follows (for example). 
     1. Server Farms: Server farms can have multiple servers which require redundant backup of the data stream (packets). In this case, the servers could reside on separate ports (output ports of VLAN D) of the switch  100  but they each would receive the same data (packets) simultaneously, at wire rate, with very little configuration and very little resource overhead. 
     2. Redundant Firewalls: Redundant firewalls need to see the same traffic (packets), so that they can provide redundancy. With the present invention, the switch  100  can route the data (packets) out to both firewalls simultaneously with no CPU overhead, as the routing is done in hardware. 
     In addition, the present invention has several different alternatives where a switch can receive a unicast packet (which has a router MAC address) in a first VLAN and then multicast/flood copies of the packet (after it had been routed and modified to have a multicast MAC address) from a second VLAN. These alternative embodiments are as follows (for example): 
     1. The present invention could be expanded to cover multi-chip systems, where the switch  100  can use a loopback port that is located on another chip (note: the switch  100  described above was assumed to have one chip that was associated with the aforementioned VLANS, ports, loopback port, ingress/forwarding logic unit, and routing tables). In this alternative embodiment, the routing tables in one chip can be configured to route the packet to a loopback port on a remote chip, if the local chip does not have a free loopback port. The packet would traverse from the local chip to the remote chip, using the same mechanism it does for normal routing, viz. fabric/HiGig ports of the switch  100 . 
     2. The current implementation of the switch  100  uses a single loopback port  108  to route packets  102  that are received at all of the front panel ports  104  which are associated with VLAN A. This implementation where only one loopback port is used can reduce the bandwidth available to individual data streams (packets  102 ) because there are multiple front panel ports  104  associated with VLAN A which can receive the data streams. To increase the bandwidth, the switch  100  can have multiple loopback ports which are configured as a single linkagg. This results in the switch  100  essentially having a loobacked Linkagg. In this case, the routing tables would now be configured to route the traffic (packets) to the linkagg, as opposed to a single loopback port. In another alternative embodiment, the switch  100  could be configured to have multiple ports to be in a loopback mode, and configured to have the routing tables point to an ECMP table which would cause the packets  102  to use an ECMP route (based on a hashing scheme) where different loopback ports would be selected based on different hashings. 
     3. The present invention can also be extended since it is now possible for a FFP (Fast Filter Processor) to classify/process a packet twice because it ingresses the switch  100  two different times (see point  1  and  3 ). In particular, the FFP can now classify the packet twice and thus apply multiple rules to the same packet (pre-routing and post routing rules). For instance, the FFP/TCAM on Firebolt chips currently process packets on the ingress, pre-routing. In some cases it would also be desirable to process the packet after it is routed, after the packet has been modified by the routing process, so as to possibly identify traffic going to different next hops. The present invention enables an operator to use the FFP to process a packet a second time if desired after it has been routed. As a result, the operator could now apply policies which, for example, prioritize or rate-limit the traffic (packet) if it is destined to a certain next hop. Without the loopback method  200  of the present invention this is not possible to do today. 
     Although several embodiments of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it should be understood that the present invention is not limited to the disclosed embodiments, 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.