Abstract:
Systems and methods according to the exemplary embodiments enable improved switch or link failure handling. A redundant router master/backup status change may be triggered based on switch connectivity. According to an exemplary embodiment, a method is provided. The method includes monitoring a connectivity of a network, detecting a failure, and based on the detected failure, changing the redundant router master/backup status of both a first router and at least a second of router.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to networking and in particular to triggering a redundant router master/backup status change based on switch connectivity. 
       BACKGROUND 
       [0002]    In current deployed transport networks, such as mobile transport networks, layer 2 transport switches may be used as aggregation sites to aggregate traffic from different cell sites and fixed access sites. 
         [0003]    In packet backbone networks, site routers may be adopted at the edge of layer 2 networks (e.g., aggregation sites) to transmit layer 2 switch traffic to layer 3 Internet Protocol/Multiprotocol Label Switching (IP/MPLS) backbone networks (layer 3 networks). In other words, the site routers may act as a bridge from layer 2 to layer 3. 
         [0004]    For example, as shown in  FIG. 1 , multiple layer 2 switches  104 - 116  may construct a site  102  (layer 2 network) having a ring topology closing with dual site routers  120 ,  122 . Multiple routers  120 ,  122  may be used to provide static routing redundancy towards the layer 2 network  102  to protect against single point failures. The multiple routers  120 ,  122  may use Virtual Router Redundancy Protocol (VRRP). According to VRRP, one of the multiple routers  120 ,  122  may have a master/backup status as master and the remaining router or routers may have a master/backup status as backup. Upon failure of the router that has the master/backup status as master, a redundant router master/backup status change may occur and the backup router or one of the backup routers may then have a master/backup status as master. 
         [0005]    Integrated Routing and Bridging (IRB) may combine router functionality with switch functionality in the dual site routers  120 ,  122 . The Ethernet interfaces between the layer 2 transport switches (client nodes) and the Ethernet interfaces between the routers may be configured as layer 2 interfaces. IRB provides the ability to route between a bridged domain and a routed domain with Bridge Group Virtual Interface (BVI). BVI may be used on the routers  120 ,  122  towards the layer 2 switches. 
         [0006]    In an aggregation site including switches and routers, Ethernet Ring Protection (ERP) may act as a ring protection mechanism to provide sub-50 ms protection and recovery switching for Ethernet traffic in a ring topology, and also ensure that no loops are formed at the Ethernet layer. A Ring Protection Link (RPL) Owner Node is responsible for blocking traffic at one end of the RPL to secure link switching during link failure or a recovery condition within the Ethernet ring so that traffic may move towards a layer 3 network  124 . 
         [0007]    In an aggregation site, such as the aggregation site  102  shown in  FIG. 1 , ERP is normally supported by the switches  104 - 116 . In order to provide resilience within the whole ring, ERP may be used if all the switches  104 - 116  support the ERP feature. Alternatively, some switches may not support the ERP feature and may run Spanning-Tree Protocol (STP). In such an instance, an ERP-capable switch can send a Topology Change Notification Bridge Protocol Data Unit (TCN BPDU) to non-ERP switches triggering a MAC Forwarding Database (FDB) flush. 
         [0008]    In an aggregation site, such as the aggregation site  102  shown in  FIG. 1 , once a link or switch failure occurs, the layer 2 network ring will switch based on a configured resilience mechanism such as ERP switching. The failed link or switch will be blocked and traffic will instead go through the unblocked protection link towards the layer 3 network  124  through the site routers  120 ,  122 . For example, as shown in  FIG. 1 , no switch or link failure has occurred. The layer 2 network ring is such that, for example, traffic from switch  106  is directed through switches  108 ,  110 ,  112 .  FIG. 2  shows the same aggregation site  102  as in  FIG. 1  after a link failure. Specifically, the link between switches  110  and  112  is shown as failed. Thereafter, the layer 2 network ring changes and traffic from switch  106  is redirected through switches  104 ,  116 ,  114 . 
         [0009]    However, there remains a need for improvement with respect to switch or link failure handling. 
       ABBREVIATIONS/ACRONYMS 
       [0000]    
       
         BVI Bridge Group Virtual Interface 
         ERP Ethernet Link Protection 
         CCM Connectivity Check Message 
         CFM Connectivity Fault Management 
         IP Internet Protocol 
         IRB Integrated Routing and Bridging 
         MEPs Maintenance End Points 
         MPLS Multiprotocol Label Switching 
         RPL Ring Protection Link 
         TCN Topology Change Notification 
         VRRP Virtual Router Redundancy Protocol 
       
     
       SUMMARY 
       [0021]    Systems and methods according to the exemplary embodiments enable improved switch or link failure handling. A redundant router master/backup status change may be triggered based on switch connectivity Among other advantages and benefits, an exemplary embodiment of the present invention may provide for decreased bandwidth consumption on inter-router physical links between redundant routers. 
         [0022]    According to an exemplary embodiment, a method is provided. The method includes monitoring a connectivity of a network, detecting a failure, and based on the detected failure, changing the redundant router master/backup status of both a first router and at least a second router. The monitoring is of a network including a plurality of switches, links between the plurality of switches, and a plurality of routers. The plurality of routers are redundant routers with a first router including a master/backup status of master and at least a second of the plurality of routers including a master/backup status of backup. The detecting of a failure is of one of the plurality of switches or links between the plurality of switches. The changing of the redundant router master/backup status is of both the first router and the at least a second of the plurality of routers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The accompanying drawings illustrate various aspects of exemplary embodiments which are described herein, wherein: 
           [0024]      FIG. 1  is a schematic representation of a conventional network. 
           [0025]      FIG. 2  is a schematic representation of the network of  FIG. 1  with a failure. 
           [0026]      FIG. 3  is a schematic representation of a network. 
           [0027]      FIGS. 4-6  are schematic representations of a network according to an exemplary embodiment of the present invention. 
           [0028]      FIG. 7  is a schematic representation of a method according to an exemplary embodiment of the present invention. 
           [0029]      FIG. 8  is a schematic representation of a network according to another exemplary embodiment of the present invention. 
           [0030]      FIG. 9  is a schematic representation of a network according to another exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The following description of the exemplary embodiments of the present invention refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. 
         [0032]    Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0033]    In a network such as the aggregation site  102  shown in  FIG. 2 , once the layer 2 network ring has switched based on the configured resilience mechanism and traffic has been redirected, traffic patterns may be adversely affected. This may be due to the change caused by the switch or link failure. For example, in addition to the traffic from switches  104 ,  116 ,  114 , traffic from switch  106  may also have to travel through router  120  to router  122  to get to the layer 3 network  124 . This is due to the master/backup status of router  120  as backup and router  122  as master. While the traffic flows through routers  120 ,  122  may have been desirable before the link failure, the traffic flows through the routers  120 ,  122  are adversely affected by the link failure due to a lack of a master/backup status change of the routers  120 ,  122  in response to the new traffic pattern. For example, bandwidth utilization may be less efficient. This may be especially so in the event of a switch or link failure close to a router having a master/backup status of master. A desirable traffic pattern for the failure scenario shown in  FIG. 2  is shown in  FIG. 3 . As shown in  FIG. 3 , traffic from switches  206 ,  204 ,  216 ,  214  travel through router  220  to get to the layer 3 network  224 . This is possible due to the modified master/backup status of router  220  as master and router  222  as backup. The may lead to, for example, fifty-percent bandwidth being saved relative to the scenario shown in  FIG. 2 . Accordingly, exemplary embodiments described herein provide for, among other things, triggering a redundant router master/backup status change based on switch connectivity. 
         [0034]      FIG. 4  is a schematic representation of a network  400  according to an exemplary embodiment of the present invention. The network  400  may be a mobile transport network. The network  400  may include a layer 2 network  402  and a layer 3 network  404 . The layer 2 network  402  may be an aggregation site to aggregate traffic from different cell sites and fixed access sites. The layer 3 network  404  may be a packet backbone network such as an IP/MPLS network. 
         [0035]    The layer 2 network  402  may include multiple layer 2 switches  405 - 416 . The switches  405 - 416  may be arranged in a ring topology closing with multiple routers  420 ,  422 . The multiple routers  420 ,  422  may be used to provide static routing redundancy towards the layer 2 network  402  to protect against single point failures. The multiple routers  420 ,  422  may use VRRP. At a first point in time, the master/backup status of router  422  may be master and the master/backup status of router  420  may be backup. 
         [0036]    The switches  405 - 416  may support ERP. Alternatively, some switches may not support the ERP feature and may run Spanning-Tree Protocol (STP). In such an instance, an ERP-capable switch can send a Topology Change Notification Bridge Protocol Data Unit (TCN BPDU) to non-ERP switches triggering a MAC Forwarding Database (FDB) flush. Focusing now on the ERP supported embodiment, switch  406  may be an RPL owner node. The link between switch  405  and switch  406  may be an RPL link  430 . The RPL link  430  may have a normal status of being blocked when no switch or link failure is detected. 
         [0037]    Each of the switches  405 - 416  and each of the multiple routers  420 ,  422  may support Connectivity Fault Management (CFM). CFM is an end to end per service instance Ethernet layer operation, administration, and management (OAM) protocol. CFM may include proactive connectivity monitoring, fault verification, and fault isolation for large Ethernet metropolitan area networks (MANs) and wide area networks (WANs). Ethernet service OAM may support fault detection through Continuity Check Messages (CCMs). CCM may support a minimum interval of 3.3 ms. 
         [0038]    An IEEE 802.1ag Maintenance Association (MA) may be configured on the network  400 . That is, a pair of Maintenance End Points (MEPs) may be configured on the layer 2 network  402 . A first MEP  432  may be on a link between router  422  and switch  412  and a second MEP  434  may be on the link between switch  406  and  408   
         [0039]    Each MEP  432 ,  434  may send out “heart-beat” style CCMs periodically. Hence, by configuring a list of expected existent MEPs, the first MEP  432  can detect the health status of its connection to the second MEP  434 , and the second MEP  434  can detect the health status of its connection to the first MEP  432 . CCMs may pass through the whole link between switch  406 , which may be the RPL owner node, and router  422 , which has a master/backup status of master. Once a link or switch failure occurs, such failure may cause the first MEP  432  of router  422  to no longer receive CCMs from the second MEP  434  of the switch  406  continuously. This lack of receiving CCMs continuously may indicate the failed status of some portion of the path between MEP  432  and MEP  434 . It is conceivable that embodiments of the present invention may involve alternative fault detection mechanisms. For example, Bidirectional Forwarding Detection (BFD) may be used if a switch could support BFD. 
         [0040]    An exemplary operation of the network  400  is now described with reference to  FIGS. 4-6 , which are schematic representations of the network  400  of  FIG. 4 , and  FIG. 7  which is a schematic representation of a method  700  according to an exemplary embodiment of the present invention. 
         [0041]    In operation  704 , a connectivity of the network may be monitored. In operation  706 , it may be determined if failure of one of the switches  405 - 416  or links between the switches has occurred, e.g., by failure of an MEP to receive CCMs. 
         [0042]    In  FIG. 4 , the network of  400  is shown with no switch or link failure. In the absence of a failure of a switch or a link between switches  405 - 416 , ERP may not block any link, and the RPL link  430  may remain in its default status of being blocked. Accordingly, a first traffic flow  440  travels from switch  405  through switches  416  and  414  and through routers  420  to router  422  to get to the layer 3 network  404 . A second traffic flow  442  travels from switch  406  through switches  408 - 412  to router  422  to get to the layer 3 network  404 . 
         [0043]    Focusing on the routers, router  422  (first MEP  432 ) may send out CCMs to the switch  406  (second MEP  434 ) and the switch  406  may send out CCMs to the router  422 . As no switch or link failure has occurred, the CCMs may be received by the router  422  from the switch  406  and by the switch  406  from the router  422 . Accordingly, no switch or link failure may be detected. 
         [0044]    If in operation  706 , it is determined that no failure of one of the switches  405 - 416  or links between the switches has occurred, the method may proceed to operation  708 . In operation  708 , the redundant router master/backup status of the routers  420 ,  422  may remain in a default status. Specifically, the redundant router master/backup status of the routers  420 ,  422  may remain such that router  420  has the redundant router master/backup status of backup, and router  422  has the redundant router master/backup status of master. As the redundant router master/backup status of the routers  420 ,  422  has remained in the default status, traffic flows with respect to the routers  420 ,  422  remain unchanged. Specifically, the first traffic flow  440  travels from switch  405  through switches  416  and  414  and through router  420  to router  422  to get to the layer 3 network  404 . The second traffic flow  442  travels from switch  406  through switches  408 - 412  to router  422  to get to the layer 3 network  404 . 
         [0045]    In  FIG. 5 , the network  400  is shown after a link failure. Specifically, the link between switches  410  and  412  is shown as failed. Upon the failure of the link between switches  410  and  412 , ERP on switch  410  may block the failed link, and the RPL link  430  may be changed from its default status of being blocked to being open. Accordingly, the second traffic flow from switch  406  may no longer travel through switches  408 - 412  to router  422  to get to the layer 3 network  404 , but instead may travel through switches  405 ,  416 , and  414 , and through router  420  to router  422  to get to the layer 3 network. 
         [0046]    Focusing on the routers, router  422  (the first MEP  432 ) may send out CCMs to the switch  406  (second MEP) and the switch  406  may send out CCMs to the router  422 . Due to the link failure between switches  410  and  412 , the CCMs from the switch  406  may not be received by the router  422 . Accordingly, router  422  detects the link failure occurring between switch  406  and router  422 . 
         [0047]    If in operation  706 , it is determined that a failure of one of the switches  405 - 416  or links between the switches has occurred, the method may proceed to operation  710 . In operation  710 , the master/backup status of the routers  420 ,  422  may be changed (e.g., switched) if the status has not already been switched. Specifically, the redundant router master/backup status of the routers  420 ,  422  may be changed such that router  420  has the redundant router master/backup status of master, and router  422  has the redundant router master/backup status of backup. As the redundant router master/backup status of the routers  420 ,  422  has changed relative to the default status, traffic flows with respect to the routers  420 ,  422  may change. Specifically, the first traffic flow  440  travels from switch  405  through switches  416  and  414  to router  420  to get to the layer 3 network  404 . The second traffic flow  442  travels from switch  406  through switches  405 ,  416 , and  414  to router  420  to get to the layer 3 network  404 . Neither the first traffic flow  440  nor the second traffic flow  442  may need to travel through the router  420  to the router  422  due to the master/backup status of the routers having been changed. It should be noted that even though the master/backup status of the routers  420 ,  422  may change, router  422  may continue to be the first MEP. 
         [0048]    After operations  708  or  710 , the method  700  may return to operation  704 . As noted above, a connectivity of the network may be monitored in operation  704 . In operation  706 , it may be determined if failure of one of the switches  405 - 416  or links between the switches has occurred. 
         [0049]    In  FIG. 6 , the network  400  is shown after a link failure recovery. Specifically, the link between switches  410  and  412  (shown in  FIG. 5 ) has been recovered. Upon the recovery of the failed link between switches  410  and  412 , ERP on switch  410  may no longer block the recovered link, and RPL link  430  may return to its normal status of being blocked. Accordingly, the second traffic flow  442  from switch  406  may again travel from switch  406  through switches  408 - 412  and router  422  to router  420  (not shown in  FIG. 6 ) to get to the layer 3 network  404 . 
         [0050]    Focusing on the routers, router  422  may continue to be the first MEP despite having had its master/backup status switched to backup. Router  422  may send out CCMs to the switch  406  (second MEP) and the switch  406  may send out CCMs to the router  422 . As the link between switches  410  and  412  has been recovered, the CCMs may be received by the router  422  from the switch. Accordingly, router  422  detects recovery of the link (i.e., no switch or link failure may be detected). 
         [0051]    As noted above, the method may proceed to operation  708  if it is determined that no failure of one of the switches  405 - 416  or links between the switches has occurred. In operation  708 , the redundant router master/backup status of the routers  420 ,  422  may revert to a default status. Specifically, the redundant router master/backup status of the routers  420 ,  422  may revert such that router  420  has the redundant router master/backup status of backup, and router  422  has the redundant router master/backup status of master. As the redundant router master/backup status of the routers  420 ,  422  reverts to the default status, traffic flows with respect to the routers  420 ,  422  also revert. Specifically, the a first traffic flow  440  travels from switch  405  through switches  416  and  414  and through router  420  to router  422  to get to the layer 3 network  404 . The second traffic flow  442  travels from switch  406  through switches  408 - 412  to router  422  to get to the layer 3 network  404 . 
         [0052]    It should be noted that the pair of MEPs may be different. The choice of the MA between an ERP switch and a VRRP master should be performed carefully to facilitate desirable traffic distribution. The MA should not span over the RPL link but may be placed close to the RPL owner or RPL node respectively as shown in  FIG. 8 . Additionally, CFM messages may be configured in a same Virtual Local Area Network which may be used for Ring Automatic Protection Switching (R-APS) messages of ERP without a need to change a MA as shown in  FIG. 9 . 
         [0053]    The preceding describes an approach for triggering a redundant router master/backup status change based on switch connectivity. However, it will be appreciated by those skilled in the art that the preceding is not intended to be exhaustive. For example, the approach for triggering a redundant router master/backup status change based on switch connectivity may be applicable in an embodiment including multiple ERP rings that may be connected by common dual site routers. In such an embodiment, each ERP ring may have its own VRRP instance on the dual site routers. In another example, traffic outage time for ERP and VRRP switching may be decreased. Because an ERP switch may be independent of a VRRP switch, one method to decrease total traffic outage time maybe to cause both of these changes (ERP switch and VRRP switch) to start in parallel. Accordingly the total traffic outage time caused by both of these changes may not exceed more than a maximum time of failure over time from an ERP switch and a VRRP switch respectively. In an exemplary embodiment, a timer may be introduced for time coordination on the VRRP router. Accordingly, a start time for an ERP switch and a VRRP switch may be adjusted by related parameters such as a CCM interval of link detection in an ERP switch, a CCM interval of link detection in a VRRP switch, an advertise interval for VRRP advertisements between a VRRP master and backup routers and the new timer introduced on VRRP router that may ensure that an ERP switch and a VRRP switch run in parallel as much as possible which may lead to less disturbance for an entire system. 
         [0054]    The preceding embodiments provide for a number of advantages and benefits. For example, bandwidth consumption on the inter-router physical links may be decreased, especially in the case of a switch or link failure close to a redundant router having a master/backup status of master. This may save physical bandwidth resources of routers, especially in the case of where VRRP requires redundancy link protection between site routers. Additionally, switch or link failure detection by a redundant router may be fast due to the utilization of CFM. As CCMs may be supported to 3.3 ms, a redundant router may detect a switch or link status change quickly and adjust a master/backup relation between redundant routers accordingly. Additionally, traffic latency across inter-router links may be decreased. After a redundant router master/backup status change, all traffic from a layer 2 network may not need to pass through a link between the redundant routers thereby reducing traffic latency. 
         [0055]    Systems and methods for processing data according to exemplary embodiments of the present invention may be performed by one or more processors executing sequences of instructions contained in a memory device. Such instructions may be read into the memory device from other computer-readable mediums such as secondary data storage device(s). Execution of the sequences of instructions contained in the memory devices may cause the processor to operate, for example, as described above. In alternative embodiments, hard-wire circuitry may be used in place of or in combination with software instructions to implement the present invention. 
         [0056]    The above-described exemplary embodiments are intended to be illustrative in all respects, rather than restrictive, of the present invention. Thus the present invention is capable of many variations in detailed implementation that can be derived from the description contained herein by a person skilled in the art. All such variations and modifications are considered to be within the scope and spirit of the present invention as defined by the following claims. No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Also, as used herein, the article “a” is intended to include one or more items.