Abstract:
A method for managing flow of packets comprises inputting a plurality of flow rules of various priorities to a router having a plurality of hardware resources, the plurality of hardware resources having varying levels of capability relative to each other. A first rule, for example a rule having a lowest priority, may be selected from among the plurality of flow rules, and it may be determined whether the first rule conflicts with any lower priority rules stored in the hardware resource with a highest capability. If the first rule conflicts with a lower priority rule in the hardware resource with the highest capability, the first rule may be stored in the resource with the highest capability. If the first rule does not conflict with a lower priority rule in the hardware resource with the highest capability, the first rule may be processed to identify the hardware resource with a lowest capability that can support the first rule, and the first rule may be stored in the identified resource.

Description:
BACKGROUND OF THE INVENTION 
     Enterprise or data center networks are often large, and run a wide variety of applications and protocols. Forwarding behaviors of packets on a router in such networks are governed by policies, generated by routing protocols, such as BGP, ISIS, OSPF, or network manager. Each policy is described as a flow rule, which comprises a flow identifier, an action, and a priority. 
     The flow identifier defines the set of packets the policy is applied to, and consists of a set of tuples. Each tuple corresponds to a header field (e.g. source IP, destination IP, source port, destination port and etc), and has a value and mask to support wild-card matching. For instance, a policy generated by BGP has (destination_ip, mask) as the flow identifier. 
     The action specifies the forwarding behaviors (e.g. egress port, destination MAC, class of service, counter action) of packets to be implemented by the router if the packet matches the flow identifier. When a packet qualifies for multiple flow rules, its forwarding behavior is dictated by the rule with highest priority. 
     Routers often provide multiple hardware tables for implementing flow rules, such as a Media Access Control (MAC) table, LPM, an MPLS table, and an ACL table. The hardware tables may vary in size from one router to the next. The ACL table is often a more expensive hardware resource on the router, because it can classify traffic using much wider flow identifiers (200˜300 bits in the packet header) than MAC/LPM/MPLS tables (20˜48 bits in the packet header). Additionally, because of its capabilities, the ACL table is most often used to store flow rules for forwarding packets. Accordingly, a system and method for more efficiently managing the flow of packets on a router is desired. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention provides a method for managing flow of packets, comprising inputting a plurality of flow rules of various priorities to a router having a plurality of hardware resources, the plurality of hardware resources having varying levels of capability relative to each other. For example, one resource may have increased packet identification capabilities relative to another resource. A first rule, for example a rule having a lowest priority, may be selected from among the plurality of flow rules, and it may be determined whether the first rule conflicts with any lower priority rules stored in the hardware resource with a highest capability. If the first rule conflicts with a lower priority rule in the hardware resource with the highest capability, the first rule may be stored in the resource with the highest capability. If the first rule does not conflict with a lower priority rule in the hardware resource with the highest capability, the first rule may be processed to identify the hardware resource with a lowest capability that can support the first rule, and the first rule may be stored in the identified resource. Further, it may be determined whether any rules stored in at least one resource of the plurality of hardware resources are unnecessary, and such unnecessary rules may be removed from the at least one resource. A rule may be determined to be unnecessary if it is a subset of another rule and has a lower priority than that other rule. 
     Additionally or alternatively, it may be determined whether the first rule conflicts with any other lower priority rules implemented on the router, and if not, the priority of the first rule may be decreased. Similarly, it may be determined whether the first rule conflicts with any other higher priority rules implemented on the router, and if not the priority of the first rule may be increased. 
     Another aspect of the invention provides a method for managing flow of packets, comprising adding a flow rule to a router having a plurality of hardware resources storing flow rules of various priorities, the plurality of hardware resources having varying levels of capability relative to each other. The added rule may be processed to identify a lowest capability hardware resource in which the added rule can be stored, and the added rule may be stored in the identified resource. If the added rule is stored in a highest capability resource, any higher priority rules may be moved from a lower capability resource into the highest capability resource if such higher priority rules overlap with the added rule. Further, it may be determined whether the added rule is a subset of another higher priority rule on the router, and if so, the rule may be added to a deprecated rule set. Even further, it may be determined whether any rules stored in the highest capability resource are redundant, and any redundant rules may be removed from the resource and added to the deprecated rule set. 
     Yet another aspect of the invention provides a method for managing flow of packets, comprising selecting a flow rule for deletion from a router having a plurality of hardware resources storing flow rules of various priorities, the plurality of hardware resources having varying levels of capability relative to each other. The hardware resource in which the selected rule is stored may be identified, and the selected rule may be removed from the identified hardware resource. If the selected rule is removed from a highest capability resource, additional rules may be moved from the highest capability resource to a lower capability resource if such rules can be supported by the lower capability resource and do not conflict with any rules of the same priority in the lower capability resource. 
     Another aspect of the invention provides a system for managing flow of packets in a router, comprising an input capable of receiving packet flow rules of various priorities, a plurality of hardware resources having varying levels of capability relative to each other, and a processor programmed to implement flow rules received at the input into the plurality of hardware resources. The processor may implement the flow rules by selecting a first rule having a lowest priority, determining whether the first rule conflicts with any lower priority rules stored in the resource with a highest capability, storing the first rule in the resource with the highest capability if the first rule conflicts with a lower priority rule in the resource with the highest capability, and processing the first rule to identify the hardware resource with the lowest capability that can support the first rule if the first rule does not conflict with a lower priority rule in the resource with the highest capability, and storing the first rule in the identified resource. The hardware resources may be a MAC table, an MPLS table, and LPM table and an ACL table, wherein the ACL table is the highest capability resource. The varying levels of capability of the plurality of resources may be packet identification capabilities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a system diagram according to an aspect of the invention. 
         FIG. 2  is a flow diagram according to an aspect of the invention. 
         FIG. 3  is a flow diagram according to another aspect of the invention. 
         FIG. 4  is a flow diagram according to another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     According to an aspect of the invention, a flow manager mechanism implements flow rules using the least amount of hardware resources (e.g., ACL, LPM, MPLS, and MAC table entries). For example, a set of rules may be processed in relation to one another by the flow manager to produce the result of a smaller but equivalent set of rules. Additionally, the flow manager may adjust priorities of flow rules in relation to one another and may determine in which hardware resource each flow rule should reside to minimize usage of more expensive resources (e.g., the ACL table). 
       FIG. 1  shows a system  100  including a server  180  connected to clients  160 - 164  and server  166  through a network  150 . The network  150  includes a number of routers  142 ,  144 ,  146 . The router  144  includes memory  120  including a number of resources, such as packet forwarding tables. According to one aspect, these packet forwarding tables may include media access control (MAC) table  122 , longest prefix match (LPM) table  124 , multi protocol label switching (MPLS) table  126 , and access control list (ACL) table  128 . Of these resources, some may be more costly than others. One possible reason may be that some resources have higher capabilities (e.g., can control traffic based on a wider variety of identifiers, such as source IP, source port, destination IP, destination port, etc.). For example, the ACL table  128  may have the highest capability, and thus be the most expensive resource, because it is capable of storing a wider variety of packet routing rules than the Mac table  122 , the LPM table  124 , or the MPLS table  126 . Accordingly, resources in the memory  120  may be managed by flow manager  130  to use the resources most efficiently. 
     The MAC table  122  may have a lookup key (e.g., denoted as mac_lookup_key) for retrieving actions stored in corresponding MAC table entries (e.g., denoted as mac_action). The lookup key may also correspond to an identification of an ingressing packet. For example, the lookup key for the MAC table  122  may be {VID, DA}, wherein VID is the Virtual Local Area Network (VLAN) identifier and DA is the destination MAC address. Accordingly, when {VID, DA} of an ingressing packet matches the key of a MAC table entry, the corresponding mac_action is assigned to the packet. The action is often equal to {egress_port}, and specifies to which egress_port in the router the packet should be forwarded. On some router hardware, a counter is available to track the number of packets matching a particular MAC table entry. In this instance, mac_action takes the form {egress_port, inc_counter}. 
     Similar to the MAC table  122 , the LPM table  124  in an ipv4/ipv6 network may also have a lookup key, denoted as lpm_lookup_key. This lookup key may take the form {VRF_id, DIP}, wherein DIP is the destination Internet Protocol address. Each LPM table entry specifies an action, denoted as lpm_action, which may take the form {egress_port} or {egress_port, inc_counter}. 
     The MPLS table  126  may also have a lookup key, denoted as mpls_lookup_key, in the form {VRF_id, ingress_port, mpls_label}. The mpls_label field of an MPLS packet identifies the destination of packet, similar to a destination IP address. Each MPLS table entry specifies an action denoted as mpls_action to be applied to the port, which may be {egress_port, command} or {egress_port, command, inc_counter}. The command may be push/pop/swap. 
     The ACL table  128  may have a lookup key denoted as acl_lookup_key. This may take the form of any of a number of routing schemes, such as src_ip/mask, destination_ip/mask, src_port/mask, dest_port/mask, src_mac/mask, dest_mac/mask, etc. The action specified by the ACL table entry is denoted as acl_action, which may include egress_port, change_cos, inc_counter, etc. The change_cos field changes the class of service of packets. 
     A packet ingressing the router  144  goes through a packet processing pipeline, where first L2 processing is performed, then L3 processing, and then ACL processing. During L2 processing, the packet will be matched against the MAC table  122 . If mac_action.egress_port is a physical port on the router or drop instead of l3_router, the packet skips L3 processing (during which the packet is matched against the MPLS table  126  or the LPM table  124 ) and is then matched against the ACL table  128 . Otherwise, the packet is matched against the LPM table  124  or the MPLS table  126 , depending on the packet type. After L2/L3 processing, the packet is matched against the ACL table  128 . If it matches an ACL table entry, the corresponding acl_action assigns the ultimate outgoing port from which the packet is forwarded to egress from the router  144  onto the next router  146  or the destination host (e.g., client  162 ). For example, the packet may be assigned acl_action.egress_port. This may override any egress port (e.g., mac_action.egress_port, lpm_action.egress_port, or mpls_action.egress_port) previously assigned as a result of L2/L3 processing. 
     The flow manager  130  may determine how to efficiently utilize hardware resources based on a set of principles. These principles consider two rules, hereinafter denoted as Rule A and Rule B for convenience, in relation to one another. One relationship may be that Rule A and Rule B conflict with each other, which may occur if a packet received at the router  144  would match both rules. For example, the flow identifiers for Rule A and Rule B may not overlap, but may match different fields in the packet header (e.g., A.flow_identifier={src_mac=01:00:00:00:00:00} and B.flow_identifier={dest_mac=01:00:00:00:00:00}). Alternatively, for example, the flow identifiers for Rule A and Rule B may overlap, and the common header fields may have overlapping value ranges (e.g., A.flow_identifier={src_mac=01:xx:xx:00:00:00} and B.flow_identifier={dest_mac=01:11:11:xx:xx:xx}). Another potential relationship between Rule A and Rule B is that one rule is a subset of another. For example, Rule A may be a subset of Rule B if packets matching A are a subset of those matching B. 
     According to a first principle, Rule B must be implemented in the ACL table  128  if Rule A having lower priority is implemented in the ACL table  128  and Rule A conflicts with Rule B. For example, assume Rule B is not stored in ACL table  128 . Since Rule A conflicts with Rule B, a packet p may match both Rule A and Rule B. As p goes through the packet processing pipeline, it is first matched with Rule B, for example during L2 processing, and assigned with B.action. As the packet p continues through the processing pipeline, it is then matched with lower priority Rule A, for example during ACL processing, and assigned with A.action. Accordingly, the forwarding action of p would be A.action, which would violate the definition of priority of policies. However, storing higher priority Rule B in the ACL table  128  would cause the packet p to end up with a forwarding action of B.action, and thus adhere to the defined priorities. 
     According to a second principle, if Rule B is a subset of Rule A and Rule B has lower priority than Rule A, B is redundant and may be eliminated. For example, if Rule B is a subset of Rule A, a packet p matching Rule B would also match Rule A. Because Rule A has a higher priority than B, the forwarding behavior of p is dictated by Rule A. Therefore, Rule B can be eliminated without affecting forwarding behaviors of packets. 
     According to a third principle, if a Rule A does not conflict with any other lower priority rules implemented on the router, the priority of Rule A may be decreased without affecting the forwarding behaviors of packets. For example, let S be the original rule set implemented on the router, and S′ be the new rule set with all rules in S and A assigned to a lower priority. For a packet p, R p  and R p ′ denotes the rule dictating p&#39;s forwarding action if S or S′ is implemented on the router respectively. If R p =A, A is the highest priority rule matching p. Since A does not conflict with any lower priority rules in S, p does not match with any rules of lower priorities than A in S. If A&#39;s priority is decreased, p still matches A, and therefore R p ′=A. Accordingly, R p =R p ′. If R p =B and B≠A, there are two possible cases: (1) p matches both B and A, B and has a higher priority (2) p doesn&#39;t match A. In either case, R p ′=B with A&#39;s priority lowered. 
     According to a fourth principle, if a Rule A does not conflict with any other higher priority rules implemented on the router, the priority of Rule A may be increased without affecting the forwarding behaviors of packets. Let S be the original rule set implemented on the router, and S′ be the new rule set with all rules in S and A assigned to a higher priority. For a packet p, R p  and R p ′ denotes the rule dictating p&#39;s forwarding action if S or S′ is implemented on the router respectively. If R p =A, A is the highest priority rule matching p. Since A does not conflict with any higher priority rules in S, p does not match with any rules of higher priorities than A in S. If A&#39;s priority is increased, p is still assigned with A.action, and therefore R p ′=A. Accordingly, R p =R p ′. If R p =B and B≠A, p doesn&#39;t match A, and R p &#39;=B with A&#39;s priority increased. 
     The flow manager  130  may implement flow rules generated by routing protocols or network operators based on the foregoing principles in order to minimize usage of hardware table resources on the router. According to one aspect, the flow manager  130  may manage resources during at least three events: initialization, adding a rule, and removing a rule. During initialization, the flow manager  130  receives a set of initial flow rules, and determines how to implement these rules in the MAC table  122 , the LPM table  124 , the MPLS table  126 , and the ACL table  128 . During its run-time, the flow manager  130  processes commands to add/remove a flow rule, by adding/removing rules in the MAC table  122 , LPM table  124 , MPLS table  126 , and ACL table  128 . Each of these events will be described in detail below. 
     The flow manager  130  may be a software module stored on a network router (e.g., router  144 ). Alternatively, the flow manager  130  may be stored on a separate piece of hardware connected to the router. In this regard, the flow manager may include its own processor, or may share a processor with the router. Similarly, according to one aspect, the flow manager  130  may be connected to and may manage the rule sets of a plurality of routers (e.g., routers  142 - 146 ). 
       FIG. 2  illustrates an initialization event of the flow manager  130 . The initial input to the flow manager is a set of flow rules, denoted as rule_set. Based on this input, the flow manager  130  calculates mac_rule_set, lpm_rule_set, mpls_rule_set, and acl_rule_set, denoting the rules to be added to the MAC, LPM, MPLS and ACL tables  122 - 128 . It also maintains a set of rules eliminated because they were determined to be redundant according to the second principle described above. This set of rules is denoted as deprecated_rule_set. 
     In step  205 , the flow manager  130  may run one or more functions to organize a set of rules. For example, the flow manager  130  may run a sort(rule_set), which sorts the rules in rule_set in increasing priority. The priority may be based on any predefined criteria. 
     In step  210 , the flow manager  130  selects one rule, for example Rule A, for processing. Because the rules were sorted by priority in step  205 , Rule A may have highest or lowest priority. For purposes of this example, we assume that Rule A was selected first because it has a lowest priority. 
     Once selected, in step  215  the flow manager  130  determines whether the flow identifier of Rule A may be supported by a less expensive resource. For example, the flow manager  130  determines which, if any, of the MAC, LPM, or MPLS tables  122 - 126  can support a flow of packets matching Rule A. If the flow identifier of Rule A cannot be supported by any of the MAC, LPM, or MPLS tables  122 - 126 , Rule A must be stored in the ACL table  128 , which is the most expensive table on the router. Accordingly, the method  200  skips to step  255 . 
     However, if it is determined in step  215  that the Rule A can be supported by one of the MAC, LPM, or MPLS tables  122 - 126 , the method  200  proceeds to step  220  where it is determined if the Rule A conflicts with any lower priority rule in the ACL table  128 . For example, is_conflict(A, acl_rule_set) determines if Rule A conflicts with a lower priority rule in acl_rule_set. In the event that there is such a conflict, Rule A must be stored in the ACL table  128  also, and so the method skips to step  255 . If there is no such conflict, the method  200  proceeds to step  225 . 
     In steps  225 - 245 , a “sanity check” is performed. This sanity check determines whether the action of Rule A can be supported by the MAC, MPLS and LPM tables  122 - 126 , respectively. While this check may have been performed during step  215  while determining which table could support the flow identifier of Rule A, performing this check later provides assurance that the Rule is placed in the least expensive resource which can support it. Performing this check later may also increase the processing time for performing the method  200 . 
     In step  225 , it is determined whether the action of Rule A may be supported by the MAC table  122 . The MAC table  122  may be checked first, because it is the least expensive resource. If the MAC table  122  can support Rule A, Rule A may be stored in the MAC table  122  in step  230 , and the process will return to step  210  to select another rule for placement. However, if it is determined that the MAC table  122  cannot support the action of Rule A, the method  200  continues to check the remaining resources. 
     In step  235 , it is determined whether the action of Rule A may be supported by the next least expensive resource, here the MPLS table  124 . If the action of Rule A can be supported, Rule A is added to the MPLS table  124  in step  240 . However, if it cannot be supported, the LPM table is checked in step  245 . 
     In step  255 , is_lpm_rule(A, lpm_rule_set) returns true if A.flow_identifier is equal to lpm_lookup_key and A.action is equal to lpm_action. It further removes any rule in lpm_rule_set which is a subset of A and has a lower priority than A, and saves them into deprecated_rule_set. According to the second principle described above, such rules can be deprecated. Nevertheless, if Rule A is removed, they have to be added back to acl_rule_set, mac_rule_set, lpm_rule_set or mpls_rule_set. If the LPM table  126  can support the action of Rule A, Rule A is added to the LPM table  126  in step  250 . Otherwise, Rule A must be added to the last remaining table and the most expensive resource, the ACL table  128 , in step  255 . 
     After a rule is added to the ACL table  128 , additional steps may be performed to reduce the number of rules stored in the ACL table  128 . For example, prune(A, acl_rule_set, mac_rule_set, lpm_rule_set, mpls_rule_set) removes any rule in acl_rule_set, mac_rule_set, lpm_rule_set, mpls_rule_set which is a subset of A and has a lower priority than A, and saves them into deprecated_rule_set. 
       FIG. 3  illustrates a method  300  for adding a rule using the flow manager  130 . For example, a Rule B that was not initialized in step  205  may be added. According to this method  300 , the flow manager  130  will perform a series of additional steps to determine whether and how to store Rule B. 
     In step  310 , it is determined whether the added Rule B is valid. For example, a rule may be valid only if it does not conflict with any other rule of the same priority. Accordingly, the flow manager may perform the function is_valid(A, l2_rule_set, l3_rule_set, mpls_rule_set, acl_rule_set). The l2_rule_set includes mac_rule_set. The l3_rule_set is the union of lpm_rule_set and mpls_rule_set. Accordingly, this function will return false if the added Rule B overlaps with any rule of the same priority in l2_rule_set, l3_rule_set, and acl_rule_set, in which case the method  300  ends and the rule is not added. However, if there is no such conflict, the function will return true and the process will proceed to step  315 . 
     In step  315 , it is determined whether the added Rule B is needed, or whether it would be redundant. For example, a function is_deprecated(B) may be performed. This function returns true if Rule B is a subset of another higher priority rule in l2_rule_set, l3_rule_set, or acl_rule_set. In that case, the Rule B may be considered redundant, and moved into the deprecated rule set in step  320 . However, if the function is_deprecated(B) returns false, and it is determined that the Rule B is needed, the method  300  proceeds to step  325 . 
     In step  325 , it is determined if the Rule B must be stored in the ACL table  128 . For example, it may be necessary to store Rule B in the ACL table  128  if its flow identifier or action is not supported by the MAC, LPM, or MPLS table  122 - 126 . It may also be necessary to store Rule B in the ACL table  128  if it conflicts with any rules of lower priority already stored in the ACL table  128  (i.e., acl_rule_set). Accordingly, a function is_acl_rule(B, acl_rule_set) may be performed to determine whether either of these circumstances are present. If so, the function will return true, and the added Rule B will be stored in the ACL table  128  in step  330 . 
     If it is determined in step  325  that Rule B does not need to be stored in the ACL table  128 , the method  300  proceeds to steps  350 - 360 , where the most appropriate storage table for Rule B is determined. For example, in step  350 , it is determined whether it is necessary to store the Rule B in either of the L3 processing tables (LPM table  124  or MPLS table  126 ). Similar to the determination in step  325 , this determination may be made by performing a function is_l3_rule(B, l3_rule_set), which returns true if Rule B&#39;s flow identifier or action is not supported by the MAC table  122 , or if Rule B conflicts with any rules of lower priority in the LPM or MPLS tables  124 ,  126 . If this function returns true, Rule B is stored in the L3 rule set (step  360 ), and thus is included in either the LPM table  124  or the MPLS table  126 . However, if the function is_l3_rule(B, l3_rule_set) returns false, thus indicating that Rule B need not be stored in one of the L3 processing tables  124 - 126 , Rule B is stored in the MAC table  122  in step  355 . 
     If Rule B is moved into the ACL table  128  in step  330 , another set of processing steps  332 - 344  is performed to determine whether any rules from the MAC, LPM, or MPLS tables  122 - 126  must be moved into the ACL table  128  also. 
     In step  332 , a temporary rule set is defined as all the rules in the MAC, LPM, and MPLS tables  122 - 126  having higher priority than Rule B. In some circumstances, there may be no rules that fit such a definition. Accordingly, in step  334  it is determined whether any rules are present in the temporary rule set. For example, the function temp_rule_set.empty( ) may return true if there are no rules in the MAC or L3 rule sets with higher priority than Rule B, and false if at least one such rule exists. If the function returns true, signifying that no rules exist in the temporary rule set, the method  300  proceeds to step  336  to determine if any rules in any of the tables may be considered redundant and moved into a deprecated rule set before ending. If the function returns false, the method  300  proceeds to step  340 . 
     In step  340  a Rule C from the temporary rule set is selected for analysis. In step  342 , it is determined whether Rule C is an ACL rule and must be stored in the ACL table  128 . For example, the function is_acl_rule(C,acl_rule_set) may return true if Rule C cannot be supported by any of the MAC, LPM, or MPLS tables  122 - 126 , or if Rule C overlaps with a lower priority rule in the ACL rule set. In this case, the Rule C may be removed from the MAC or L3 rule set in step  344  and added to the ACL table  128 . However, if it is determined in step  342  that Rule C is not an ACL rule, the process returns to step  334  to determine if there are any other rules in the set for analysis. 
       FIG. 4  illustrates a method  400  for removing a Rule A using the flow manager  130 . For example, network topology changes could trigger re-computation of routing protocols, as a result of which flow rules could be removed. Accordingly, the flow manager  130  may perform a series of checks to ensure that removing the Rule A will not affect forwarding behaviors of packets not matching Rule A. For example, the flow manager  130  may determine that rules previously deprecated in step  336  during the addition of Rule A should now be added into ACL, MPLS, LPM, or MAC tables  122 - 128 . 
     In steps  405 - 425  it is determined in which table the Rule A to be removed is currently stored. Specifically, in step  405 , a check of MAC table  122  is performed to determine whether the Rule A is stored therein. If so, the Rule A is removed from the rule set stored in the MAC table  122  in step  410 . If not, the method  400  proceeds to step  415 . 
     In step  415 , the ACL table  128  is checked for Rule A. If it is determined that the Rule A is present in the ACL table  128 , it is removed from the table in step  425 . However, if Rule A is not in the ACL table  128 , it must be in one of the L3 processing tables (i.e., LPM table  124  or MPLS table  126 ). Accordingly, the Rule A is removed from the L3 rule set in step  420 . 
     Once the Rule A has been removed, a further series of processing steps may be performed depending on which table the Rule A was removed from. If the Rule A was removed from the MAC rule set or the L3 rule set, a series  430  of steps may be performed to determine whether any rules from the deprecated rule set must be restored into the MAC, LPM, or MPLS table  122 - 126 . If Rule A was removed from the ACL rule set, a series  450  of steps may be performed to determine if any other rules in the ACL table  128  may be moved into one of the MAC, LPM, or MPLS tables  122 - 126 . 
     In step  432  of the series  430 , a temporary rules set is defined as the deprecated rule set (e.g., the rules that were removed as redundant according to the second principle described above). In step  434 , it is determined whether there are any rules in the deprecated rule set. For example, the function temp_rule_set.empty( ) may return true if there are no rules in the deprecated set, and false if at least one rule is present. For example, there may be no rules and the function would return true if none of the rules initialized in the method  200  were considered redundant in the pruning step  260 . In this case, the method  400  for removing a rule may be ended. However, if the function returns false indicating that at least one rule is present in the deprecated set, the series  430  continues to step  436 . 
     In step  436 , a first Rule B from the deprecated rule set is selected for analysis. In step  438 , deprecated Rule B is compared to the removed Rule A to determine whether Rule B is a lower priority subset of Rule A. If it is not, Rule B may remain in the deprecated rule set, and the series  430  returns to step  434  to determine if there are any other rules in the deprecated rule set for analysis. If Rule B is determined to be a lower priority subset of Rule A in step  438 , Rule B may be removed from the deprecated rule set in step  440  and added back to one of the tables (e.g., in accordance with method  300 ) in step  442 . 
     Now turning to the series  450 , in step  452  the temporary rules set includes all rules in ACL table that have higher priority than rule A. The temporary rule set is further sorted in increasing priority, and the rules within it are analyzed individually starting with a lowest priority rule to determine if they can be moved to the MAC, LPM or MPLS tables  122 - 126 . For example, a rule in the temporary rule set can be moved from ACL table  128  to one of the MAC, LPM or MPLS tables  122 - 126  if it no longer overlaps with any lower priority rules in ACL table  128 . 
     In step  454 , it is determined whether the temporary rule set is empty. If so, the method  400  returns to the series  430  to find any rules in the deprecated rule set that must be restored. If not, however, the series  450  proceeds to step  456 , where a Rule B is selected from the temporary rule set. 
     In step  458 , it is determined whether Rule B must be stored in the ACL table  128 . For example, it may be determined whether Rule B can be supported by the MAC, LPM, or MPLS tables  122 - 126 . Alternatively or additionally, it may be determined whether Rule B overlaps with any rules of lower priority in the ACL rule set. If Rule B cannot be supported by another table, or if Rule B still conflicts with another lower priority rule in the ACL rule set, Rule B may be considered an ACL rule, and thus may remain in the ACL table  128 . Accordingly, the series  450  returns to step  454  to determine if there are any other rules to analyze. However, if this is not the case, Rule B may be removed from the ACL rule set in step  460  and inserted into either the MAC rule set or the L3 rule set. 
     The above-described flow manager system and methods for initializing, adding, and removing rules in the hardware resources of a router is beneficial in that it minimizes usage of more expensive hardware resources, such as the ACL table  128 , which promoting usage of less expensive resources such as the MAC table  122 . In this regard, storage and processing capabilities of routers may be increased. In turn, networks may be capable of handling increased transmissions and overall transmission time may be reduced. Additionally, the cost of implementing networks may be reduced because the resources will be used most efficiently. 
     Although the present invention has been described with reference to particular embodiments, it should be understood that these examples are merely illustrative of the principles and applications of the present invention. For example, the present invention may be used to efficiently implement rules generated according to any of a number of routing protocols, such as BGP, ISIS, OSPF, network manager, etc. Moreover, it should be understood that the described system and method may be implemented over any network, such as the Internet, or any private network connected through a router. For example, the network may be a virtual private network operating over the Internet, a local area network, or a wide area network. Additionally, it should be understood that numerous other modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.