Abstract:
The present invention relates to a system for managing a plurality of multi-field classification rules. The system provides a first table that includes a plurality of entries corresponding to a plurality of rules relating to an ingress context and a second table that includes a plurality of entries corresponding to a plurality of rules relating to an egress context. The system also includes a network processor for classifying packets of information, wherein the network processor is programmed to utilize the first table and the second table to identify any rules relating to the ingress context and any one rules relating to the egress context that match a search key.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Under 35 USC §120, this application is a continuation application and claims the benefit of priority to U.S. patent application Ser. No. 10/832,958, filed Apr. 27, 2004, entitled “Method for Managing Multi-Field Classification Rules Relating to Ingress”, all of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to computer systems, and more particularly to a system for managing multi-field classification rules relating to ingress and egress contexts. 
       BACKGROUND OF THE INVENTION 
       [0003]      FIG. 1  depicts conventional networks  10  and  20  which may be connected to the Internet  30 . Each network  10  and  20  includes host  12 ,  14  and  16  and  22  and  24 , respectively. Each network  10  and  20  also includes a switch  18  and  26 , respectively, and may include one or more servers such as the servers  17 ,  19  and  28 , respectively. In addition, each network  10  and  20  may include one or more gateways  13  and  25 , respectively, to the Internet  30 . Not explicitly shown are routers and other portions of the networks  10  and  20  which may also control traffic through the networks  10  and  20  and which will be considered to be inherently depicted by the switches  18  and  26 , respectively, and the networks  10  and  20  in general. 
         [0004]      FIG. 2  depicts a portion of a typical switch  50 , which may be used for the switches  18  and  26  ( FIG. 1 ) and/or a router (not shown). The switch  50  includes a network processor  52  and storage  54 . The switch  50  typically also includes other components (not shown). The network processor  52  manages functions of the switch  50 , including the classification of packets using the rules described below. The storage  54  retains data relating to the rules. 
         [0005]    Referring to  FIGS. 1 and 2 , in order to manage communications in a network, such as the network  10  or  20 , filter rules are used. Filter rules are typically employed by switches, routers and other portions of the network to perform packet classification. Each filter rule is used to classify packets which are being transmitted via a network in order to determine how the packet should be treated and what services should be performed. For example, a filter rule may be used in testing packets entering the network from an outside source to ensure that attempts to break into the network can be thwarted. For example, traffic from the Internet  30  entering the network  10  may be tested in order to ensure that packets from unauthorized sources are denied entrance. 
         [0006]    Similarly, packets from one portion of a network may be prevented from accessing another portion of the network. For example, a packet from some of the hosts  12 ,  14  or  16  may be prevented access to either the server  17  or the server  19 . The fact that the host attempted to contact the server may also be recorded so that appropriate action can be taken by the owner of the network. 
         [0007]    Such filter rules may also be used to transmit traffic based on the priorities of packets. For example, packets from a particular host, such as the host  12 , may be transmitted because the packets have higher priority even when packets from the hosts  14  or  16  may be dropped. The filter rules may also be used to ensure that new sessions are not permitted to be started when congestion is high even though traffic from established sessions is transmitted. Other functions could be achieved based on the filter rule as is well known to those skilled in the art. 
         [0008]    In order to determine whether a particular rule will operate on a particular packet, a key is tested. The key typically includes selected fields, known collectively as the TCP/IP 5-tuple or just the 5-tuple, extracted from the Internet Protocol (IP) and TCP headers of the packet. The IP and TCP headers typically contain five fields of interest: the source address (SA), the destination address (DA), the source port (SP), the destination port (DP) and the protocol. These fields are typically thirty-two bits, thirty-two bits, sixteen bits, sixteen bits and eight bits, respectively. Rules typically operate on one or more of these fields. For example, based on the source and/or destination addresses, the rule may determine whether a packet from a particular host is allowed to reach a particular destination address. 
         [0009]    In addition to the fields of the TCP/IP 5-tuple, the key can also include additional fields that are related to service-level agreements, e.g., Quality of Service (QoS). In particular, the key can include fields for an ingress context and an egress context. A context may refer to a port number, a VLAN number, VPN number, ATM Virtual Circuit Number, or some combination of these and other possible session identification parameters. Thus, filter rules relating to an ingress or egress context also include additional bits (fields) corresponding to the ingress and egress contexts. 
         [0010]    In testing a key against a filter rule, it is determined whether the filter rule should be enforced against the packet associated with the key. The key is tested by comparing specified fields for the key of the packet with a range(s) of values defined by the filter rule. Each rule contains a range of values in one or more dimensions. Each dimension corresponds to a field of the key (typically the IP header). One type of filter rule has a range consisting of a single value or a spread of values. In such a case, a “Range-rule” search is performed to determine whether the key exactly matches the value for the rule. Other rules have ranges which can be expressed using a single prefix. The prefix is a binary number containing a number of ones and zeroes (1 or 0), followed by place holders, or wildcards (*). In this case, a “Wildcard-match” is performed to determine whether the rule applies to the packet. 
         [0011]    Testing the key against a filter rule can be a tedious and time consuming procedure, which is multiplied several times over when the number of filter rules increases. In order to expedite this process, a search facility known as a “Software-managed tree” (SMT) search engine is utilized. Generally, the SMT search engine analyzes a collection of filter rules, and based on the rules&#39; conditions, builds a plurality of binary tree structures. Each tree structure is a binary tree that includes a series of hierarchical single bit test nodes and leaf nodes. At each single bit test node, a specified bit of the key is tested, and depending on the value of the test bit, a path is followed, which terminates at a leaf. Each leaf includes a filter rule that includes the rule specification and defines an action to be taken with regard to a packet. The SMT search engine is described in more detail in U.S. Pat. No. 6,298,340, entitled, “SYSTEM AND METHOD AND COMPUTER PROGRAM FROM FILTERING USING TREE STRUCTURE” issued on Oct. 2, 2001, and assigned to the assignee of the present invention. 
         [0012]    The SMT search engine enables a search on multiple fields within the key, and within each field, looks for either a pattern under a mask (Wildcard match), or a range specified by a minimum or a maximum (Range-rule), as the criteria for declaring a match. The search engine can utilize standard memory structures resulting in an economical implementation. Nevertheless, utilizing such memory structures presents issues. For example, characteristics of the tree structures contribute to excessive latency in completing the searches and contribute to an inefficient use of storage space. Thus, utilizing standard memory structures, while economical, makes it very difficult to support multi-field classification in an SMT engine. 
         [0013]    Current solutions to this issue include utilizing a ternary content addressable memory (TCAM). TCAMs include logic, such as a comparator, for each location. The logic allows the entries of the TCAM to be searched in parallel. Nevertheless, although TCAMs provide high-performance multi-field classification, they also add significant costs to a system. 
         [0014]    Accordingly, what is needed is a system for providing high-performance multi-field classification utilizing standard memory structures. The system should implement an improved search facility that maintains the cost advantage of using standard memory structures, while improving performance to approach that of a more expensive TCAM solution. The present invention addresses such a need. 
       SUMMARY OF THE INVENTION 
       [0015]    The present invention relates to a system for managing a plurality of multi-field classification rules. The system includes providing a first table that includes a plurality of entries corresponding to a plurality of rules relating to an ingress context and providing a second table that includes a plurality of entries corresponding to a plurality of rules relating to an egress context. The system also includes utilizing the first table and the second table to identify any rules relating to the ingress context and any rules relating to the egress context that match a search key. 
         [0016]    Through aspects of the system of the present invention, a direct table of filter rules is partitioned into two tables, one for filter rules relating to an ingress context and another for rules relating to an egress context. The ingress context or the egress context is used as an index into each respective table. By partitioning the filter rules relating to a context in such a manner, the duplication of tree sub-structures is eliminated, thereby reducing the total number of nodes in binary tree structure. Moreover, the number of nodes that need to be traversed to distinguish among ingress rules and among egress rules are significantly reduced. Accordingly, with the system of the present invention, performance levels utilizing standard memory structures approach those in systems utilizing a TCAM. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a diagram of computer systems of networks in which the present invention can be used. 
           [0018]      FIG. 2  is a diagram of a switch in which the present invention can be used. 
           [0019]      FIG. 3  is a block diagram of an SMT binary tree structure. 
           [0020]      FIG. 4  is a block diagram of separate ingress and egress binary tree structures according to a preferred embodiment of the present invention. 
           [0021]      FIG. 5  is a block diagram illustrating the restructured search key according to a preferred embodiment of the present invention. 
           [0022]      FIG. 6  is a flowchart illustrating a method for filtering according to a preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The present invention relates to computer systems, and more particularly to a system for managing multi-field classification rules related to ingress and egress contexts. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. For example, although the present invention will be described in the context of filter rules, one of ordinary skill in the art will readily recognize that the system can operate effectively for other multi-field classification rules. Likewise, while the present invention is described in the context of a DRAM memory subsystem, one of ordinary skill in the art will readily recognize that the system can operate effectively for other types of memory subsystems (e.g., SRAM). Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and features described herein. 
         [0024]      FIG. 3  is a block diagram of an SMT binary search tree structure  300 . As is shown, the tree structure  300  comprises a plurality of single bit test nodes, referred to as pattern search control block (PSCB) nodes, e.g.,  300   a - 300   m , and leaf nodes, e.g.,  310   f - 310   m . Although only 13 PSCB nodes and 7 leaf nodes are depicted, those skilled in the art readily appreciate that the tree structure  300  can include fewer than or greater than 13 PSCBs and 7 leafs, and that the tree structure  300  depicted in  FIG. 3  is merely illustrative. 
         [0025]    The tree structure  300  in  FIG. 3  begins with PSCB Node  0  ( 300   a ), i.e., PSCB Node  0  ( 300   a ) is the root node of the tree structure  300 . Typically, root nodes, e.g.,  300   a , are stored in entries ( 30   x ,  30   y ) of a table, known as a Direct Table  30 . Each PSCB node, e.g.,  300   b , is typically 36 bits and includes a Next Bit to Test (NBT) field  302   b  and an address field  304   b . The NBT field  302   b  indicates which bit in the key to test. The address field  304   b  includes a pointer that points to either a pair of PSCB nodes, e.g.,  300   d ,  300   e , or a leaf, e.g.,  310   a.    
         [0026]    Pointers that point to PSCBs are referred to as next pattern address (NPA) pointers (e.g.,  304   b ) and pointers that point to a leaf are referred to as leaf control block address (LCBA) pointers (e.g.,  306   f ). For example, the address field  304   a  for PSCB Node  0  ( 300   a ) includes an NPA pointer ( 304   a ) to a pair of PSCB nodes, Node  1  ( 300   b ) and PSCB Node  2  ( 300   c ), which are stored in adjacent address spaces. Which PSCB node (Node  1  ( 300   b ) or Node  2  ( 300   c )) to follow depends on the value of the key bit indicated by the NBT field  302   a . Inevitably, a PSCB node, e.g.,  300   f , includes an LCBA pointer  306   f  that points to a leaf  310   a . As stated above, the leaf  310   a  includes the filter rule that defines the action to be taken with regard to a packet. 
         [0027]    Typically, the Direct Table  30  includes entries for all filter rules regardless of whether they are related to ingress contexts (referred to as ingress rules) or egress contexts (referred to as egress rules). This organization, however, presents problems because ingress and egress rules do not generally overlap relative to search key bits used to distinguish one entry from another. For example, in  FIG. 3 , two (2) ingress rules (IR 1  and IR 2 ) and two (2) egress rules (ER 1  and ER 2 ) are analyzed. The first bit test, as defined in the NBT field  302   a  of the DT entry corresponding to Node  0  ( 300   a ), determines which one of two PSCB nodes ( 300   b  or  300   c ) is selected, and distinguishes between IR 1  and IR 2 . The test bit, however, is irrelevant as to which egress rule (ER 1  or ER 2 ) is valid. Therefore, both egress rules (ER 1  and ER 2 ) may still be valid choices regardless of which PSCB node (Node  1  ( 300   b ) or Node  2  ( 300   c )) is selected. 
         [0028]    From PSCB Node  1  ( 300   b ), the NPA  304   b  points to Node  3  ( 300   d ) and Node  4  ( 300   e ), where ER 1  is distinguished from ER 2 . Nevertheless, because the test bit ( 302   b ) used in this decision is irrelevant to IR 1 , IR 1  may still be a valid choice regardless of which PSCB node (Node  3  ( 300   d ) or Node  4  ( 300   e )) is selected. Only at the next level is IR  1  distinguished from ER  1  and ER 2 . For instance, from Node  3  ( 300   d ), the NPA  304   a  points to Node  7  ( 300   h ) and Node  8  ( 300   i ), where IR 1  is distinguished from ER 1 . The test bit ( 302   d ) determines which node ( 300   h  or  300   i ) is selected. Node  7  ( 300   h ) includes an LCBA pointer  306   h  to a leaf node  310   h  including IR 1  and Node  8  ( 300   i ) includes a pointer  306   i  to the leaf node  310   i  including ER 1 . 
         [0029]    From Node  2  ( 300   c ), the NPA  304   c  points to Node  5  ( 300   f ) and Node  6  ( 300   g ), where IR 2  is separated from ER 1  and ER 2 . Node  5  ( 300   f ) includes an LCBA pointer  306   f  to a leaf node  310   f  including IR 2 , but Node  6  ( 300   g ) does not distinguish ER 1  and ER 2 . Accordingly, Node  6  ( 300   g ) includes an NPA pointer  304   g  to Node  13  ( 300   l ) and Node  14  ( 300   m ), where ER 1  is distinguished from ER 2 . The test bit  302   g  in Node  6  ( 300   g ) determines which node ( 300   l  or  300   m ) is selected. Node  13  ( 300   l ) includes an LCBA pointer  306   l  to a leaf node  310   l  including ER 1  and Node  14  ( 300   m ) includes a pointer  306   m  to the leaf node  310   m  including ER 2 . 
         [0030]    For the simple four rule example above, three (3) decision nodes are required in order to resolve the four rules. For any one search, at least two (2) decision nodes (e.g., Node  2  ( 300   c ) and Node  5  ( 300   f )) must be traversed. As is shown in  FIG. 3 , the tree structure  300  requires six node pairs, and a typical search would require traversing three (3) node pairs. Moreover, several PSCB nodes point to the same rule, e.g., Node  7  ( 300   h ) and Node  9  ( 300   j ) point to leaf nodes ( 310   h ,  310   j ) including IR 1 . This duplication consumes memory. 
         [0031]    Depending on the number of ingress and egress rules and other factors, the SMT tree structure  300  can be much more complex than the tree structure  300  depicted in  FIG. 3 . Indeed, in practical implementations, hundreds (and even thousands) of rules are managed, thereby increasing the tree structure&#39;s complexity exponentially and creating significant storage and performance problems (e.g., excess latency). Accordingly, the existing binary tree structure  300  depicted in  FIG. 3  contributes to excessive latency, and also inefficiently utilizes memory. 
         [0032]    According to a preferred embodiment of the present invention, a system is provided for improving latency and memory utilization by partitioning ingress and egress rules into separate Direct Tables. By separating ingress rules and egress rules, the resulting tree structures for each type of rule is significantly simplified. In particular, sub-tree structures are not duplicated and the number of nodes traversed is greatly reduced. Accordingly, memory utilization and latency are improved. 
         [0033]    To describe more fully the system of the present invention, please refer to  FIG. 4 , which is a block diagram of separate ingress and egress binary search tree structures according to a preferred embodiment of the present invention. As is shown, the direct table  30  in  FIG. 3  is divided into two separate tables, an ingress context direct table  40  and an egress context direct table  40 ′. The ingress context direct table  40  includes a plurality of entries ( 40   x ,  40   y ) corresponding to every possible ingress context. Although not shown, the direct table  40  can also include null entries that do not correspond to an ingress context. According to the preferred embodiment of the present invention, each of the plurality of entries comprises a root PSCB node, e.g., Ingress Node  0  ( 400   a ), of a small tree structure. The small tree structure includes one or more leaf nodes ( 410   a ,  410   b ), where each leaf, e.g.,  410   a , is associated with at least one ingress rule. Each PSCB node in the tree structure, including the root ( 400   a ), comprises the NBT field  402   a  and pointer field, as usual. Here, however, each test bit, e.g.,  402   a , explicitly distinguishes between ingress rules if the pointer field includes an NPA pointer  404   a . Accordingly, if two ingress rules (IR 1  and IR 2 ) are presented, only one node pair (Ingress Node  1  ( 400   b ) and Ingress Node  2  ( 400   c )) is required to distinguish between IR 1  and IR 2 . Notably, none of the sub-tree structures are duplicated. Naturally, if any of the nodes, including the root ( 400   a ), includes an LCBA pointer  406   b , the node points directly to the leaf node. 
         [0034]    Similarly, the egress rule direct table  40 ′ includes a plurality of entries ( 40   x ′,  40   y ′) corresponding to every possible egress context, as well as null entries (not shown). Each of the plurality of entries includes a root node, e.g., Egress Node  0  ( 400   a ′), of a tree structure for at least one egress rule. Similarly, each test bit, e.g.,  402   a ′, in an Egress Node, e.g.,  400   a ′, explicitly distinguishes between egress rules if the pointer field includes an NPA pointer  404   a ′. Accordingly, if two egress rules (ER 1  and ER 2 ) are presented, only one node pair (Egress Node  1  ( 400   b ′) and Egress Node  2  ( 400   c ′)) is required to distinguish between ER 1  and ER 2 . Again, none of the sub-tree structures are duplicated. 
         [0035]    The direct table (DT) for either the ingress rules  40  or egress rules  40 ′ is sized according to the number of bits in the context field of the rule. Thus, if the ingress context is 12 bits, the ingress rule DT  40  has 4096 (2 12 ) entries, where each entry ( 40   x ,  40   y ) defines a small tree structure for distinguishing ingress rules related to a corresponding ingress context. 
         [0036]    By providing a separate ingress context DT  40  and egress context DT  40 ′, ingress and egress rules, e.g., IR 1 , IR 2 , ER 1  and ER 2 , can be fully distinguished in fewer node pairs. For example,  FIG. 4  illustrates that four (4) rules are distinguished in two node pairs, in contrast to the six node pairs depicted in  FIG. 3 . Fewer nodes need to be traversed to resolve a search for either an ingress rule or egress rule match, thereby reducing latency. Also, none of the sub-tree structures are duplicated, thereby reducing memory consumption. While two searches are required for an ingress/egress rule pair, such searches can be performed in parallel, further minimizing overall latency. Thus, the improvement in performance and savings in memory consumption far outweigh any issues related to performing two parallel searches, particularly when applied to large rule sets. Moreover, because the context can be quite large, e.g., between 16 and 20 bits, resolving those bits in the respective DT ( 40 ,  40 ′) rather than one bit at a time in a tree structure ( FIG. 3 ) significantly accelerates the search process. 
         [0037]    To further improve performance and reduce memory consumption, the preferred embodiment of the present invention restructures the search key.  FIG. 5  is a block diagram illustrating the restructured search key according to a preferred embodiment of the present invention. Typically, as stated above, the key  500  includes the TCP/IP 5-tuple fields  502 , e.g., SA, DA, SP, DP and Protocol, and fields for ingress context  504  and egress context  506 . According to the preferred embodiment of the present invention, an ingress context key  500 ′ and an egress context key  500 ″ are constructed from the original key  500 . The ingress context key  500 ′ is formed by placing the ingress context  504  at the beginning of the key  500 ′ and removing the egress context  506 . The egress context key  500 ″ is formed similarly except that the egress context  506  is placed at the beginning of the key  500 ″ and the ingress context  504  is removed. 
         [0038]    According to a preferred embodiment of the present invention, the ingress  504  and egress  506  contexts are mapped directly to the ingress context DT  40  and the egress context DT  40 ′, respectively. Thus, the ingress context  504  in the ingress context key  500 ′ is used to index directly into the ingress context DT  40 . Likewise, the egress context  506  in the egress context key  500 ″ is used to access the egress context DT  40 ′. Indexing directly into the ingress or egress context DT ( 40 ,  40 ′) via the respective ingress  504  or egress  506  context significantly accelerates the search process because the context is resolved in the ingress or egress context DT ( 40 ,  40 ′). 
         [0039]    Moreover, because the ingress  504  or egress  506  context is mapped to the respective direct table ( 40 ,  40 ′), neither context needs to be stored in the rules. Accordingly, specifications corresponding to the ingress context  504  and egress context  506  in a rule definition can be eliminated, thereby reducing the size of the rule definition. Such a reduction allows more capacity for action data or packing multiple rule definitions in a common structure, such as a leaf node. In addition, because the rule definition now has fewer bits, validation is simpler, i.e., a full compare between the rule definition and the key is easier because fewer bits are required, thereby accelerating the search process. 
         [0040]      FIG. 6  is a flowchart illustrating a method for filtering according to a preferred embodiment of the present invention. Referring to  FIG. 5  and  FIG. 6 , in step  600 , the search engine receives a search command that includes the search key  500 . The search key  500  is then used to generate the ingress context key  500 ′ (step  602 ) and the egress context key  500 ″ (step  604 ). The search engine then utilizes the ingress context key  500 ′ to perform a first multi-field classification search from the ingress context DT  40  in step  606 . Likewise, the search engine utilizes the egress context key  500 ″ to perform a second multi-field classification search from the egress context DT  40 ′ in step  608 . Because the first and second searches are independent, i.e., there are no interdependences between the two searches, the first and second searches (steps  606  and  608 ) can be performed in parallel in order to minimize overall latency for completion of the process. The results, i.e., action data corresponding to the rule(s) matching the keys ( 500 ′ and  500 ″), from the first and second searches are returned in step  610 . 
         [0041]    A system for managing multi-field classification rules related to ingress and egress contexts is disclosed. In a first aspect, the direct table is partitioned into separate ingress context and egress context direct tables for rules relating to ingress and egress contexts respectively. By partitioning the direct table in this manner, the number of nodes needed to fully distinguish ingress or egress rules is significantly reduced and the duplication of sub-tree structures is eliminated. This reduction in the number of nodes simplifies the tree structure and requires less memory to store the tree structure. Moreover, because fewer nodes need to be traversed to resolve the search, the search process is accelerated, thereby improving performance. 
         [0042]    According to another aspect, the search key is restructured into two keys, an ingress context key and an egress context key. The ingress context key includes the ingress context at the beginning of the key. The ingress context is used to index directly into the ingress context DT. Likewise, the egress context key is used to index directly into the egress context DT. By using the full context to index directly into the respective DT, the context is resolved in the DT and the search process is accelerated. 
         [0043]    Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the present invention. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.