Patent Publication Number: US-6987735-B2

Title: System and method for enhancing the availability of routing systems through equal cost multipath

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to network processor-based devices, and more specifically to an improved equal cost multipath routing and recovery mechanism that enables the routing system to recover more quickly that the routing protocol. 
   2. Discussion of the Prior Art 
   In today&#39;s networked world, bandwidth is a critical resource. Increasing network traffic, driven by the Internet and other emerging applications, is straining the capacity of network infrastructures. To keep pace, organizations are looking for better technologies and methodologies to support and manage traffic growth and the convergence of voice with data. 
   The convergence of voice and data will play a large role in defining tomorrow&#39;s network environment. Because voice communications will naturally follow the path of lowest cost, voice will inevitably converge with data. Technologies such as Voice over IP (VoIP), Voice over ATM (VoATM), and Voice over Frame Relay (VoFR) are cost-effective alternatives in this changing market. However, to make migration to these technologies possible, the industry has to ensure quality of service (QoS) for voice and determine how to charge for voice transfer over data lines. 
   Integrating legacy systems is also a crucial concern for organizations as new products and capabilities become available. To preserve their investments in existing equipment and software, organizations demand solutions that allow them to migrate to new technologies without disrupting their current operations. 
   Eliminating network bottlenecks continues to be a top priority for service providers. Routers are often the source of these bottlenecks. However, network congestion in general is often mis-diagnosed as a bandwidth problem and is addressed by seeking higher-bandwidth solutions. Today, manufacturers are recognizing this difficulty. They are turning to network processor technologies to manage bandwidth resources more efficiently and to provide the advanced data services, at wire speed, that are commonly found in routers and network application servers. These services include load balancing, QoS, gateways, fire walls, security, and web caching. 
   For remote access applications, performance, bandwidth-on-demand, security, and authentication rank as top priorities. The demand for integration of QoS and CoS, integrated voice handling, and more sophisticated security solutions will also shape the designs of future remote access network switches. Further, remote access will have to accommodate an increasing number of physical mediums, such as ISDN, T1, E1, OC-3 through OC-48, cable, and xDSL modems. 
   A network processor (herein also mentioned as an “NP”) has been defined as a programmable communications integrated circuit capable of performing one or more of the following functions:
         Packet classification—identifying a packet based on known characteristics, such as address or protocol;   Packet modification—modifying the packet to comply with IP, ATM, or other protocols (for example, updating the time- to-live field in the header for IP);   Queue/policy management—reflects the design strategy for packet queuing, de-queuing, and scheduling of packets for specific applications; and,   Packet forwarding—transmission and receipt of data over the switch fabric and forwarding or routing the packet to the appropriate address.       

   For exemplary purposes, reference is made to  FIG. 1  which illustrates a logical model of a generic Network Processor system  10 . As shown in  FIG. 1 , multiple Network Processors (NP)  12  are shown connected using a switch fabric  15 , with each of the network processors supporting a large number of external LAN or WAN interface ports  20 . A separate General Purpose Processor (GPP) functions as a control point (CP)  25  for the system and has a physical or logical association with all of the Network Processors  12  in the system for enabling the customization and configuration of the Network Processor (NP) devices so that they may handle the forwarding of data packets and frames. It should be understood however, that the GPP may be embedded in a network processor device itself. The generic network processor system  10  comprises two major software components: 1) the control point code base running on the GPP, and, the programmable hardware-assist processors&#39; picocode in each of the network processors. These two software components are responsible for initializing the system, maintaining the forwarding paths, and managing the system. From a software view, the system is distributed. The GPP and each picoprocessor run in parallel, with the CP communicating with each picoprocessor using a predefined application program interface (API)  30  and control protocol. 
   The CP code base provides support for the Layer  2  and Layer  3  topology protocols and Layer  4  and Layer  5  network applications and systems management. Examples are protocol support for VLAN, IP, and Multiprotocol Label Switching standard (MPLS), and the supporting address- and route-learning algorithms to maintain topology information. 
   With particular reference to  FIG. 1 , and accompanying description found in commonly-owned, co-pending U.S. Pat. No. 6,769,033 entitled “NETWORK PROCESSOR PROCESSING COMPLEX AND METHODS”, the whole contents and disclosure of which is incorporated by reference as if fully set forth herein, the general flow of a packet or frame received at the NP device is as follows: frames received from an network connection, e.g., Ethernet MAC, are placed in internal data store buffers by an upside “enqueue” device (EDS-UP) where they are identified as either normal data frames or system control frames (Guided Frames). In the context of the invention, frames identified as normal data frames are enqueued to an Embedded Processor Complex (EPC) which comprises a plurality of picoprocessors, e.g., protocol processors. These picoprocessors execute logic (picocode) capable of looking at the received frame header and deciding what to do with the frame (forwardly, modify, filter, etc.). The EPC has access to several lookup tables, and classification hardware assists to allow the picoprocessors to keep up with the high-bandwidth requirements of the Network Processor. A classification hardware assist device in particular, is provided for classifying frames of well known frame formats. The Embedded Processing Complex (EPC) particularly provides and controls the programmability of the NP device and includes, among other components (such as memory, dispatcher, interlaces), N processing units, referred to as GxH, which concurrently execute picocode that is stored in a common instruction memory. It is understood, however, that the architecture and structure is completely scalable towards more GxHs with the only limitation being the amount of silicon area provided in the chip. In operation, classification results from the classification hardware assist device are passed to the GxH, during frame dispatch. Each GxH preferably includes a Processing Unit core (CLP) which comprises, e.g., a 3-stage pipeline, general purpose registers and an ALU. Several GxHs in particular, are defined as General Data Handlers (GDH) each of which comprise a full CLP with the five coprocessors and are primarily used for forwarding frames. One GxH coprocessor, m particular, a Tree Search Engine Coprocessor (TSE) functions to access all tables, counters, and other data in a control memory that are needed by the picocode in performing tree searches used in forwarding data packets, thus freeing a protocol processor to continue execution. The TSE is particularly implemented for storing and retrieving information in various processing contexts, e.g., determining frame routing rules, lookup of frame forwarding information and, in some cases, frame alteration information. 
   Traditional frame routing capability provided in network processor devices typically utilize a network routing table having entries which provide a single next hop for each table entry. Commonly-owned U.S. Pat. No. 6,721,800 entitled SYSTEM USING WEIGHTED NEXT HOP OPTION IN ROUTING TABLE TO INCLUDE PROBABILITY OF ROUTING A PACKET FOR PROVIDING EQUAL COST MULTIPATH FORWARDING PACKETS, the whole content and disclosure of which is set forth herein, describes a system and method for providing the ability for a network processor to select from multiple next hop options for a single forwarding entry. 
   FIG.  2 ( a ) depicts an example network processor frame routing scenario  40  and FIG.  2 ( b ) illustrates an example Equal Cost Multipath Forwarding (ECMP) table  50  that may be used to provide a lookup of a next hop address for forwarding packets as described in commonly-owned, co-pending U.S. patent application Ser. No. 09/546,702. Preferably, such a table is employed in a Network Processor (NP) device having packet routing functions such as described in commonly-owned, co- pending U.S. patent application Ser. No. 09/384,691. 
   Thus, the example ECMP forwarding table  50  illustrated in FIG.  2 ( b ), is particularly implemented in a frame forwarding context for network processor operations. In the example ECMP forwarding table  50 , there is provided subnet destination address fields  52 , with each forwarding entry including multiple next hop routing information comprising multiple next hop address fields, e.g., fields  60   a - 60   c . Additionally provided in the ECMP routing table is cumulative probability data for each corresponding next hop such as depicted in action data field  70 . Particularly, in the exemplary illustration of the ECMP packet forwarding table  50  of FIG.  2 ( b ), there is included three (3) next hop fields to addresses 9.1.1.1, 8.1.1.1, 6.1.1.1 associated with a destination subnet address 7.*.*.*. An action data field  70  includes threshold values used to weight the probability of each next hop and is used to determine which next hop will be chosen. In the action field  72 , shown in FIG.  2 ( b ), these values as being stored as cumulative percentages with the first cumulative percentage (30%) corresponding to next hop  0 , the second cumulative percentage value (80%) corresponding to next hop  1 , etc. This means that, the likelihood of routing a packet through next hop  0  is 30% (i.e., approximately 30% of traffic for the specified table entry should be routed to next hop  0 ), and, the likelihood of routing a packet through next hop  1  is 50% (i.e., approximately 50% of traffic for the specified table entry should be routed to next hop  1 ). This technique may be extended to offer as many next hops as desired or feasible. 
   Currently, in such network processing systems, if a destination NP device (hereinafter referred to as Targetblade or blade) or interface (such as a port or TargetPort) associated with the target blade and capable of handling the frame type fails, i.e., the packet or frame cannot be routed to the correct destination set forth in the ECMP forwarding table. However, it is often the case that the other Network Processors (NP&#39;s) in the system will continue to attempt to forward frames through the failed interface/blade until the routing protocol, e.g., the Open Shortest Path First (OSPF) protocol which enables routers to understand the internal network architecture, i.e., within an autonomous network, and calculate the shortest path from an IP Source Address (SA) to IP Destination Address (DA), detects the failed link and downloads a new forwarding entry that avoids the failed interface/blade. The time for this routing protocol to detect the failed link could be relatively long, and during this period all the data packets routed through the failed interface/blade may be lost. 
   Consequently, it would be highly desirable to provide a methodology that would enable a routing system to recover more quickly that the routing protocol so as to significantly reduce the occurrence of lost data packets to a failed target interface/blade with minimal performance penalty. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a network processor with a system that that would enable a routing system to recover more quickly that the routing protocol so as to significantly reduce the occurrence of lost data packets to a failed target interface/blade. 
   It is another object of the present invention to provide in a network processor system, a method of maintaining the operational status of all the network processors (blades) in the routing system so that packet forwarding issues resulting from a failed interface/blade may be quickly resolved without the loss of data packets routed in the system with minimal performance penalty. 
   In accordance with the preferred embodiment of the invention there is provided for a networking environment including one or more network processing (NP) devices and implementing a routing protocol for routing data packets from a source NP devices to destination NP devices via a switch fabric, with each network processing device supporting a number of interface ports, a system and method for enabling a routing system to recover more quickly that the routing protocol so as to significantly reduce the occurrence of lost data packets to a failed target interface/blade. The routing system is enabled to track the operational status of each network processor device and operational status of destination ports supported by each network processor device in the system, and maintains the operational status as a data structure at each network processing device. 
   Prior to routing packets, an expedient logical determination is made as to the operational status of a target network processing device and target interface port of a current packet to be routed as represented in the data structure maintained at the source NP device. In this manner, correct routing of packets is ensured with reduced occurrence of lost data packets due to failed target NP devices/ports. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features, aspects and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
       FIG. 1  illustrates a logical model of a generic Network Processor system  10 . 
     FIG.  2 ( a ) depicts an example network processing scenario  40  including network processors (routers) employing a packet routing table such as an ECMP forwarding table. 
     FIG.  2 ( b ) illustrates an example ECMP forwarding table for use in a network processor, router or packet switching device according to the example network processing scenario of FIG.  2 ( a ). 
       FIG. 3  illustrates the determination of a failed link to Target Blade associated with ECMP next hop destination NP 1  for the example network processing scenario of FIG.  2 ( a ), and the resulting decision to re-route the frame to an operation destination NP 2  according to the example ECMP table. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A first method of maintaining operational status at the blade/NP level involves implementation of a data structure (hereinafter referred to as opStatus) that is maintained by each NP device. This opStatus data structure includes information representing the operational status of all the network processors (blades/ports) in the routing system and, for example, may comprises a bit vector of sixty-four (64) bits long (in an example system employing 64 NP devices). If the ith bit is set, for instance, then the ith NP/blade is indicated as operational. 
   In operation, after choosing the next hop according to ECMP rules, the layer- 3  forwarding picocode will check the operational status of the NP/blade through which the chosen next hop is reachable. If that NP is not operational, then a different equal-cost next hop (the next hop with the smallest index) that is reachable through an operational NP/blade will be chosen.  FIG. 3  illustrates the determination of a failed link to Target Blade associated with ECMP next hop destination NP 1 , and the resulting decision to re-route the frame to an operation destination NP 2  according to the ECMP table. That is, in each NP, the operational status of the TB for each packet routed is checked. If the destination TB is down, then a different Next Hop is chosen as suggested by the ECMP table. It should be understood that the particular user application will detect failures and update the opStatus data structure accordingly. 
   This first solution essentially maintains the operational status at the TB (blade)/NP level. In order to extend this solution to an interface/port (TB/TP) level, there needs to be maintained a datastructure that is 64×16 bits long, assuming each blade in the example system maintains sixteen (16) ports, for instance. Since the opStatus datastructure is consulted in the main forwarding path, it must be stored in a fast, expensive memory. 
   Another solution relies on the assumption that the interface/blade failures are rare and it is unlikely that more than one blade will fail at the same time. The advantage of tracking a single failure is the reduction of the size of the opStatus data structure. The current solution only requires 48 bits in expensive high-speed memory where as the previous solution required 64×16 bits in such a memory. Thus, the following data structure may be maintained in each NP device in the routing system. 
   
     
       
         
             
           
             
                 
             
           
          
             
               { 
             
          
         
         
             
             
          
             
                 
               Uint 16 failedBlade; /* Use the value of 0xffff if all blades are 
             
          
         
         
             
             
          
             
                 
               operational */ 
             
          
         
         
             
             
          
             
                 
               Uint 16 failedPortMask; 
             
             
                 
               Uint 16 failedPortValue; 
             
          
         
         
             
          
             
               } 
             
             
                 
             
          
         
       
     
   
   According to this embodiment, the following algorithm is invoked to check whether a given TB, TP is operational: 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               Boolean is Operational (TB, TP) { 
             
             
                 
               If (failedBlade == 0xffff) 
             
          
         
         
             
             
          
             
                 
                 /* all blades are operational */ 
             
             
                 
                 return TRUE; 
             
          
         
         
             
             
          
             
                 
               If ((TB == failedBlade) &amp;&amp; (TP &amp; failedPortMask == 
             
             
                 
               failed PortValue)) 
             
          
         
         
             
             
          
             
                 
                 /* where &amp;&amp; is the logical AND operator */ 
             
             
                 
                 /* where &amp; is a bitwise AND operator*/ 
             
             
                 
                 Return FALSE; 
             
          
         
         
             
             
          
             
                 
               Else 
             
          
         
         
             
             
          
             
                 
                 Return TRUE; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   According to this algorithm, if all blades are operational, the routing of packets throughout the system will continue and no ECMP re-routing is necessary. However, only if both a Target Blade is a failed blade AND the result of the bitwise operation between the Target Port and failedPort Mask is equal to the failedPortValue, then a FALSE is returned and the ECMP table invoked for re-routing subsequent packets to another TB or TP. If a TRUE is returned, i.e., either the Target Blade is not a failed blade or the result of the bitwise operation between the Target Port and failedPort Mask is not equal to the failedPortValue, then the packet will still be routed to the destination TB/TP. 
   It should be understood that this solution may handle individual failures at port, data move unit (DMU) and blade levels. However, multiple blade failures cannot be handled by this solution. As an example, if all the interfaces in all the blades are operational then failedBlade will contain the value of 0xffff and the values of failedPortMask and failedPortValue will be ignored. If the blade number, e.g., bladeNum, is not operational (i.e., all the ports in that blade have failed) then failedBlade will include bladeNum and faildPortMask will contain the value of 0 and failedPortValue will contain the value of 0. If the port numbered portNum in the blade numbered bladeNum is not operational, then failedBlade will contain bladeNum and failedPortMask will contain the value of 0xffff and the failedPortValue will contain the value of portNum. Assuming a blade having four data move units (DMUs) of four ports each, the ports in DMU A have last (least significant) 2 bits set to 00, the ports in DMU B have last 2 bits set to 01, the ports in DMU C have last 2 bits set to 10, and the ports in DMU D have last 2 bits set to 11. If DMU C were to fail in blade numbered bladeNum, failedBlade will contain the value of bladeNum, and failedPortMask will contain the value of 0x0003 and failedPortValue will contain the value of 0x0002. 
   In the preferred embodiment, a range is used to represent the failed blades and a mask on the port number to represent the set of failed ports. This solution only requires 32 bits of high-speed memory. The following data structure will be maintained in all of the NPs in the preferred embodiment: 
   
     
       
         
             
           
             
                 
             
           
          
             
               { 
             
          
         
         
             
             
          
             
                 
               Uint 8 beginFailedBlade;/* unsigned integer representing begin 
             
          
         
         
             
             
          
             
                 
                 value range of failed blades */ 
             
          
         
         
             
             
          
             
                 
               Uint 8 endFailedBlade;/* end value of range of failed blades */ 
             
             
                 
               Uint 8 failedPortMask; 
             
             
                 
               Uint failedPortValue; 
             
          
         
         
             
          
             
               } 
             
             
                 
             
          
         
       
     
   
   According to this data structure, if failedPortMask and failedPortValue are both 0xff, then all blades will be considered operational. This convention is founded on the assumption that no port is numbered 0xff. 
   According to this embodiment, the following algorithm is invoked to check whether a given TB, TP is operational: 
   
     
       
         
             
             
           
             
                 
                 
             
           
          
             
                 
               Boolean isOperational (TB, TP) { 
             
          
         
         
             
             
          
             
                 
               If ((failedPortMask ==0xff) &amp;&amp; (failedPortValue == 0xff)) 
             
             
                 
               /* all blades are operational */ 
             
             
                 
               /* 1-cycle, 1 picocode instruction can perform this test */ 
             
          
         
         
             
             
          
             
                 
               returnTRUE; 
             
          
         
         
             
             
          
             
                 
               If (TB &lt; beginFailedBlade) return TRUE; 
             
             
                 
               If (TB &gt; endFailedBlade) return TRUE; 
             
             
                 
               If (TP &amp; failedPortMask != failedPortValue) return TRUE; 
             
             
                 
               Return FALSE; 
             
          
         
         
             
             
          
             
                 
               } 
             
             
                 
                 
             
          
         
       
     
   
   According to this algorithm, if all blades are operational, then both failedPortMask and failedPortValue are set to 0xff and the values of the other fields are ignored. This is a simple test that may be performed in one machine cycle. If the blade numbered bladeNum is not operational (i.e., all the ports in that blade have failed) then, according to this algorithm,
         beginFailedBlade and endFailedBlade are set as bladeNum,   failedPortMask is set as 0, and   failedPortValue is set as 0.       

   However, if the blades numbered, for example 8, 9, and 10 are not operational then set
         beginFailedBlade as 8   endFailedBlade as 10   failedPortMask as 0 and   failedPortValue as 0       

   If the port numbered portNum in the blade numbered bladeNum is not operational, then, according to this algorithm,
         beginFailedBlade is set as bladeNum   endFailedBlade is set as bladeNum   failedPortMask is set as 0xff   failedPortValue is set as portNum       

   The ports in DMU A have last (least significant) 2 bits set to 00. The ports in DMU B have last 2 bits set to 0 1. The ports in DMU C have last 2 bits set to 10 and the ports in DMU D have last 2 bits set to 11. In an example scenario when all the ports in DMU C fail in blade numbered bladeNum, then, according to this algorithm,
         beginFailedBlade is set as bladeNum   endFailedBlade is set as bladeNum   failedPortValue is set as 0b 0000 0010 and   failedPortMask is set as 0b 0000 0011       

   While the invention has been particularly shown and described with respect to illustrative and preformed embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention which should be limited only by the scope of the appended claims.