Abstract:
Various embodiments of the invention provide systems, devices, and methods of configuring and controlling the operation of fallback links within a network. In certain embodiments, this is accomplished by selecting an operationally active port and internally configuring it to be part of an uplink LAG to achieve minimal L2 connectivity. Compared with existing designs, the presented invention has reduced delay time, minimal impact on network traffic, increased fallback bandwidth, faster convergence, and prevents link flaps of downstream server ports. In line with the IOA&#39;s plug- and play philosophy, no administrator intervention or reprogramming of VLANs is required in selecting fallback links.

Description:
BACKGROUND 
       [0001]    A. Technical Field 
         [0002]    The present invention relates to communication networks and devices and, more particularly, to systems, devices, and methods of configuring and controlling the operation of a link fallback within a network. 
         [0003]    B. Background of the Invention 
         [0004]    A blade switch device known as I/O aggregator (IOA) is a zero-touch device that is a plug-and-play type of switch that allows administrators and users to connect a device within a server chassis and expect the device to obtain network connectivity without any further intervention by the administrator, such that once the device is connected to the chassis, the desired connectivity is established without necessitating the configuration of any additional protocols. 
         [0005]    In an IOA configuration, Link Aggregation Control Protocol (LACP) link fallback is a useful feature that aids server administrators to bring up server ports during installation and when performing troubleshooting tasks. In addition, a server administrator can, for example, verify network connectivity and server parameters without requiring input from a network administrator. 
         [0006]    Typically, during a start-up procedure, a boot protocol will automatically provision all uplink ports of the IOA into a Link Aggregation Group (LAG). However, in scenarios where no Link Aggregation Control Protocol Protocol Data Units (LACPDUs) are received on these ports, for example because the uplink (Top-of-Rack) TOR has not been configured for LAG operation yet, the LAG session is not established, and the LAG remains in an inactive state. As a consequence, based on Uplink Fault Detection (UFD), the uplink ports on the IOA are not activated, such that the state of a corresponding downlink server port interface also remains inactive. In other words, if the uplink LAG is operationally inactive, the UFD feature of the IOA negatively impacts the connectivity from the IOA to the outside world and brings down the downlink ports of the servers as well. Since the condition of the server ports is, thus, decided by the state of the uplink LAG, once the uplink ports are inactive, none of the downlink servers will have network connectivity to communicate with other network devices. 
         [0007]      FIG. 1  shows an example of a general network operating in IOA mode. System  100  comprises server chassis  102 , servers  106 , network blade switch (IOA)  108 , and TOR  112 . Server chassis  102  typically comprises up to 32 servers  106  and IOA  108 . Network connectivity between servers  106  and TOR  112  is achieved through IOA  108 . Typically, four or eight uplink ports  110  are connected to TOR  112 . Uplink ports  110  that connect IOA  108  to TOR  112  constitute a logical entity in which a set of links is grouped and serves as gateway to the outside world. Downlink ports  120  provide connectivity between IOA  108  and downstream servers  106 . 
         [0008]    Server chassis  102  is typically maintained by a server administrator, while TOR  112  is maintained by a network administrator. In operation, once the server administrator connects IOA  108  between server  106  and TOR  112 , and the network administrator configures TOR  112 , e.g., by connecting links  110  accordingly, network connectivity is established and links  110  are, at an L2 link level, are considered to be in an operationally active condition, such that the status of links  110  is discoverable by devices such as IOA  108 . 
         [0009]    By default, IOA  108  treats uplink ports  110  as LAG  114 . For LAG  114  to reach an active status, a corresponding matching LAG configuration on TOR  112  is required. Assuming an LACP configuration is present only on IOA  108 , but no corresponding configuration exists on TOR  112 , then no LACPDUs are being received from TOR  112  and no LAG session can be established resulting in LAG  114  remaining in an inactive state. Then, if uplink ports  110  on IOA  108  are inactive, for example based on UFD, the corresponding connection between downlink server  106  ports and IOA  108  also remain in an inactive state, such that none of servers  106  has network connectivity to communicate with the outside world. In order to overcome this problem, numerous attempts have been made. However, each approach has significant shortcomings. 
         [0010]    One traditional approach provides an LACP link fallback option that encompasses an internal implementation that brings down uplink port channel  110 , removes one of links  110  (e.g., port 1) from LAG  114  on IOA  108 , and then configures it as a separate, plain L2 port in order to provide network connectivity with TOR  112 . However, this approach suffers from various limitations and has additional requirements that system  100  must satisfy. First, elected port  110  has to be part of all the 4K Virtual Local Area Networks (VLANs) for L2 connectivity from the server to TOR  112 . Second, elected port  110  is to be made part of the UFD group to monitor and modify the operational status of the ports of server  106  based on the current uplink connectivity to TOR  112 . Third, elected port  110  must be programmed as a multicast router port for IGMP snooping. Fourth, election of the fallback link and L2 port can occur only after a number of trial attempts and expiration of a timeout period before confirmation can be obtained that LACPDUs are no longer received, all of which causes undesired network delays. 
         [0011]    Finally, since the uplink port channel is down, i.e., LACP LAG  114  goes inactive, while the port is removed, the ports of downlink server  106  will experience a flap, i.e., a change in activity state that temporarily halts or drops traffic until link  110  is re-activated. In fact, due to UFD, a drop in network connectivity occurs on each flap; port  110  will need to be moved back as part of the port-channel; and IGMP and 4K configurations will need to be removed from elected port  110 , further adding to the delay and slowing down convergence. 
         [0012]    One existing approach, known as LACP “force-up,” is a mechanism that allows administrators to statically choose a particular link. However, in IOA mode IOA  108 , which is plugged into server chassis  102 , will have neither preexisting information nor control over which specific uplink could be operationally active with TOR  112 , such that the static approach of designating a particular port fails in circumstances in which the port is inactive or simply not connected. 
         [0013]    In yet another existing approach, static uplink LAG  114  cannot be kept as a static LAG, as IOA  108  will have multiple uplink ports  110 , and if all are made operationally active within LAG  114 , this creates the possibility that downstream server  106  receiving multiple copies of a packet in case of Broadcast, Unknown unicast, and Multicast (BUM) traffic. 
         [0014]    What is needed are tools for network architects and administrators to overcome the above-described limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the context of these embodiments, it should be understood that this is not intended to limit the scope of the invention to these particular embodiments. 
           [0016]      FIG. 1  shows an example of a general network operating in IOA mode. 
           [0017]      FIG. 2  is an exemplary LACP link-fallback topology operating in IOA mode, according to various embodiments of the invention. 
           [0018]      FIG. 3  is an exemplary flowchart illustrating a process to obtain network connectivity using a link-fallback system operating in IOA mode, according to various embodiments of the invention. 
           [0019]      FIG. 4  illustrates an exemplary link-fallback system in a VLT topology comprising overlapping VLANs, according to various embodiments of the invention. 
           [0020]      FIG. 5  is an exemplary flowchart illustrating a process to obtain network connectivity using a link-fallback system in a VLT domain that comprises overlapping VLANs, according to various embodiments of the invention. 
           [0021]      FIG. 6  illustrates an exemplary link-fallback system in a VLT topology comprising disjoint VLANs, according to various embodiments of the invention. 
           [0022]      FIG. 7  depicts a simplified block diagram of an IOA using a link-fallback system, according to various embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    In the following description, for the purpose of explanation, specific details are set forth in order to provide an understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these details. One skilled in the art will recognize that embodiments of the present invention, described below, may be performed in a variety of ways and using a variety of means. Those skilled in the art will also recognize that additional modifications, applications, and embodiments are within the scope thereof, as are additional fields in which the invention may provide utility. Accordingly, the embodiments described below are illustrative of specific embodiments of the invention and are meant to avoid obscuring the invention. 
         [0024]    Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearance of the phrase “in one embodiment,” “in an embodiment,” or the like in various places in the specification are not necessarily referring to the same embodiment. 
         [0025]    Furthermore, connections between components or between method steps in the figures are not restricted to connections that are affected directly. Instead, connections illustrated in the figures between components or method steps may be modified or otherwise changed through the addition thereto of intermediary components or method steps, without departing from the teachings of the present invention. 
         [0026]      FIG. 2  is an exemplary LACP link-fallback topology operating in IOA mode, according to various embodiments of the invention. System  200  comprises servers  206 , IOA  208 , and TOR  212 . For clarity, components similar to those shown in  FIG. 1  are labeled in a similar manner. For purposes of brevity, a description of basic functions is not repeated here. 
         [0027]    In operation, again, assuming that there is an LACP configuration present only on IOA  208 , but no corresponding configuration exists on TOR  212 , such that no LACPDUs are being received from TOR  212 , in a manner similar to  FIG. 1 , no LAG session can be established. In these situations, in one embodiment, IOA  208  in  FIG. 2  selects and internally configures as a fallback link one of link  210  that is operationally active at the L2 level so as to ensure connectivity. IOA  208  may mark the fallback link as a static link to configure it as an operational member link of LAG  214 , i.e., statically adding the fallback link to LAG  214 , such that even if no LACP packets are transported LAG  214  continues to be active at an L2 level. Advantageously, this prevents link flaps of downstream server ports  206 . 
         [0028]    In detail, in order to ensure connectivity, selected link  210  has a known L2 level state that indicates that that link  210  is connected to another device, e.g., a peer device. IOA  208  defines that the selected link  210  is a member of uplink LAG  214 . As a result, once the server administrator connects one of links  210  to IOA  208  to establish connectivity between downstream server  206  and TOR  212 , IOA  208  detects that LAG is not configured on link  210  even if configurations on downstream server  206  may be properly made and verified. Nevertheless, IOA  208  provides basic L2-connectivity to link  210 . In addition, once the administrator configures LACP on TOR  212 , TOR  212  will commence sending LACPDUs. 
         [0029]    In one embodiment, once IOA  208  receives an LACP packet on any additional link other than selected fallback link  210 , for example in response to the administrator configuring LACP, IOA  208  removes the initially elected, static fallback link  210 , and replaces it and its function with a new, unelected link (through which the LACP packet has been received) as the current operational link in LAG  214 , which may have multiple operational members. This gives the new link preference and makes it part of LAG  214 . At this point, regular LAG functions can take over and LAG  214  continues to be active. In effect, the elected link is removed as an operational link and is replaced with the unelected link. 
         [0030]    As a result of these transitions that appear as internal state transitions within LAG  214 , the network administrator need not (re)configure or (re)program network  200  (e.g., egress programming at the ASIC to avoid undesirable loops involving traffic though uplink ports) or stop the routing of LAG traffic until LAG  214  is configured, e.g., after LCDP packets are received, in order to obtain network connectivity. 
         [0031]      FIG. 3  is an exemplary flowchart illustrating a process to obtain network connectivity using a link-fallback system operating in IOA mode, according to various embodiments of the invention. Process  300  begins at step  302  by determining that a link is inactive, for example, by determining that the LAG configuration on the IOA side of a network has no corresponding LAG configuration on the uplink port side (i.e., the uplink TOR side). 
         [0032]    At step  304 , the fallback link is elected, e.g., as a static link from uplink ports in an LACP LAG that are operationally active. (i.e., have basic L2 connection to another peer device or other device). 
         [0033]    At step  306 , the fallback link, which may be an operationally active member of a LAG, is added to the LAG. This may be accomplished by configuring the static link as part of the uplink LAG. The elected, added link serves as a fallback link, such that the LAG becomes active and packets can flow through the LAG while avoiding link flaps and without the need to reconfigure or reprogram the IOA. This is because the resulting transitions are confined internally within the LAG. 
         [0034]    At step  308 , if an unelected link receives LACP packets, the unelected link is added to the LAG and, at step  310 , the elected link is removed as an operational link from the LAG. 
         [0035]    It will be appreciated by those skilled in the art that fewer or additional steps may be incorporated with the steps illustrated herein without departing from the scope of the invention. No particular order is implied by the arrangement of blocks within the flowchart or the description herein. 
         [0036]      FIG. 4  illustrates an exemplary link-fallback system in a VLT topology comprising overlapping VLANs, according to various embodiments of the invention. System  400  comprises IOA1  402 , IOA2  404 , VLT LAG  410 ,  420 , links  412 - 418 , TOR  428 , and downstream servers  430 . Ports  412  and  414  are uplink ports that respectively connect IOA1  402  and IOA2  404  to TOR  428 , while downlink server ports  416  and  418  are connected to servers  430  to facilitate network connectivity between servers  430  and TOR  428 . IOA1  402  and IOA2  404  represent VLT nodes that, in this example, are connected via ICL  422 . 
         [0037]    In operation, IOA1  402  and IOA2  404  may operate as VLT nodes that treat uplink ports  412 - 414  as part of VLT LAG  410 . Similarly, IOA1  402  and IOA2  404  treat downlink ports  416 - 418  as part of VLT LAG  420 . In one embodiment, in response to receiving no LCAP PUD packets, each node in the VLT domain in  FIG. 4  elects a fallback link among its operationally active uplink ports  410 - 412  to be added to VLT LAG  410 . Once elected and added to VLT LAG  410 , the fallback link enables LAG  410  to carry packets. Compared to traditional approaches where only a single link can be chosen from either of the two devices (e.g.  1  out of 5+5=10 links), this embodiment in effect doubles the total fallback bandwidth available to VLT system  400  to reach TOR  428 . One of ordinary skill in the art will appreciate that the ultimate election may be made, for example, between otherwise equal operationally active links based on their lowest port numbers. 
         [0038]    In one embodiment, when VLT LAG  410  is active in the VLT domain, system  400  identifies one of VLT nodes  402 - 404  as inactive. Identification may be based on a priority-based mechanism (e.g., MAC address) that ensures that one node can be elected as the active node, thus, avoiding the possibility of deadlock. System  400  further configures an ingress mask on the identified and inactive node that, once identified, is programed to drop BUM traffic that is sent by TOR  428  and ingresses on the fallback link associated with that node. As a result, duplicate packets of BUM traffic that would otherwise reach the downstream server  430  are prevented from doing so. In other words, even if TOR  428  forwards broadcast traffic to both ports (e.g., link 1 and link 2), such that one packet will come through IOA1  402  and the other through IOA2  404 , the dropping ingressing traffic avoids duplicate BUM traffic on servers  430  connected to both IOA1  403  and IOA2  404 . 
         [0039]    In one embodiment, BUM traffic is egress-filtered on ICL  422  to prevent the forwarding of BUM traffic over ICL  422  to a VLT peer or the LAG of the VLT peer. In one embodiment, if IOA1  402  receives traffic sent by server  430  and destined for VLAN 10 (not shon) located between TOR  428  and IOA1  402 , and there are no ports on IOA2  404  that are members of VLAN 10, then ICL  422  will reject and drop traffic on IOA2  404  since there are no suitable receivers. In this operating mode, the UFD feature is disabled on both nodes  402 ,  404  to establish connectivity from downstream servers  430  that are connected to nodes  402 ,  404  to TOR  428  over a fallback link. 
         [0040]    In one embodiment, servers  430  may be connected to TOR  428  via a statically programmed portchannel bundle that has a single link as part of uplink VLT LAG  412 ,  414  in order to ensure that the VLT feature of network  400  is maintained. Once either of IOA1  402  or IOA2  404  receives an LACPDU packet, full connectivity is restored over VLT uplink LAG  410 , instead of over a single link. 
         [0041]    Conversely, in situations where uplink VLT LAG  410  receives no LACPDU packets from TOR  428 , for example, because TOR  428  has no LACP configuration, then uplink VLT LAG  410  and thus uplink ports  412 - 414  assume inactive status and no LAG session is established. As a result, due to the UFD feature, the downlink ports  416 - 418  are kept inactive, too, such that downlink servers  430  have no connectivity to TOR  428  over either IOA1  402  or IOA2  404 , even if both IOA1  402  and IOA2  404  are LACP configured. 
         [0042]    In one embodiment, in situations when the VLT uplink LAG  410  is no longer inactive, any ingress mask that may be present on the fallback link on the inactive VLT peer is removed in order to allow BUM traffic to pass over ICL  422  nondynamically. 
         [0043]      FIG. 5  is an exemplary flowchart illustrating a process to obtain network connectivity using a link-fallback system in a VLT domain that comprises overlapping VLANs, according to various embodiments of the invention. 
         [0044]    At step  502 , it is determined whether a LAG is active in the VLT domain. If so, then at step  504 , an inactive VLT peer is identified, for example, by a VLT protocol. 
         [0045]    At step  506 , an ingress mask is configured on the inactive VLT peer to drop ingressing BUM traffic on the fallback link associated with that VLT peer. 
         [0046]    At step  508 , BUM traffic is egress-filtered on an ICL connected to the node comprising the VLT peer, for example, in order to avoid forwarding of BUM traffic to another VLT peer. 
         [0047]    At step  510 , once a node receives an LACPDU packet, full connectivity is restored over entire VLT uplink LAG. 
         [0048]    At step  520 , when the LAG is inactive, an existing ingress mask is removed from the fallback link on the inactive VLT peer, so as to allow BUM traffic over the ICL, at step  522 . 
         [0049]    It will be appreciated by those skilled in the art that fewer or additional steps may be incorporated with the steps illustrated herein without departing from the scope of the invention. No particular order is implied by the arrangement of blocks within the flowchart or the description herein. 
         [0050]      FIG. 6  illustrates an exemplary link-fallback system in a VLT topology comprising disjoint VLANs, according to various embodiments of the invention. System  600  comprises TOR  602 , IOA1  604 , IOA2  606 , uplink ports  620 - 622 , downlink ports  624 - 626 , and downstream servers  610 - 612 . Uplink ports  620 - 622  are located between IOA1  604  and IOA2  606  and TOR  602 . Downlink ports  624 - 626  are located between IOA1  604  and IOA2  606  and server  610  and  612 , respectively. Typically, ICL  630  added as part of that VLAN only when both nodes IOA1  604  and IOA2  606  have a common VLAN. Although IOA1  604  and IOA2  606  are shown to be coupled via ICL  630  in  FIG. 6 , a VLAN that is present in IOA1  604  is not present in IOA  606  (e.g, VLAN10 present in IOA1  604  is not present in IOA  606 ), such that VLANs  620 - 622  are said to be disjoint VLANs. 
         [0051]    In operation, IOA1  604  act as VLT node that treats uplink ports  620  as part of a VLT LAG and downlink ports  624  as part of another VLT LAG. Similarly, IOA2  606  treats uplink ports  622  and downlink ports  626  as part of a VLT LAG. For example, IOA1  604  represents VLT node 1 that makes server  610  a member of VLAN 5, while VLT node 3 makes server  612  a member of VLAN 3. The respective uplink LAGs of VLT node 1 and 2 have port-channels that are members of VLAN 5 and VLAN 3, respectively. In one embodiment, in the VLT domain, each VLT node, i.e., IOA1  604  and IOA2  606 , independently selects one of its respective operationally active uplink ports  620 - 622  as a fallback link. Each fallback link is added to its respective LAG in order to carry traffic, thereby, doubling the fallback bandwidth available to system  600 . 
         [0052]    In one embodiment, since VLANs  620 - 622  are disjoint, ICL  630  is not programmed to be part of VLAN  620 - 622 . Therefore, BUM traffic is not sent to a VLT peer, rather BUM traffic is handled internally by each node  604 ,  606  within its own broadcast domain, such that each server&#39;s traffic over a VLAN occurs over a dedicated uplink LAG  620 - 622 . As a result, BUM traffic from one disjoint VLAN does not reach the other IOA (e.g., IOA2  606 ) via ICL  630 . 
         [0053]    In one embodiment, assuming that IOA1  604  is a member of VLAN10 and IOA2  606  is member of VLAN20, in scenarios where both fallback links of the disjoint VLAN structure  600  are selected, traffic received by one IOA (e.g., IOA1  604 ) from TOR  602  and traversing ICL  630  is usually not egress-filtered on ICL  630 . Instead, in one embodiment, an ingress mark is applied on the uplink LAG, i.e., on the LAG that connects from TOR  602  to the IOA  604 ,  606 , such that any BUM traffic can be dropped. One of the advantages when the set of disjoint VLANs operate in both nodes as shown in this example, the possibility of BUM packet duplication on downstream server  610 - 612  via ICL  630  and undesired network loops are thus prevented. 
         [0054]      FIG. 7  depicts a simplified block diagram of an IOA using a link-fallback system, according to various embodiments of the present invention. It is understood that the functionalities shown for device  700  may operate to support various embodiments of link-fallback system—although it is understood that link-fallback system may be differently configured and include different components. System  700  may include a plurality of I/O ports  705 , bus  710 , network processing unit (NPU)  715 , one or more tables  720 , and CPU  725 . The system includes a power supply (not shown) and may also include other components, which are not shown for sake of simplicity. 
         [0055]    In one embodiment, I/O ports  705  are connected via one or more cables to one or more other network devices or clients. Network processing unit  715  may use information included in the network data received at node  700 , as well as information stored in table  720 , to identify nodes for the network data, among other possible activities. In one embodiment, a switching fabric then schedules the network data for propagation through a node to an egress port for transmission to another node. 
         [0056]    It is noted that aspects of the present invention may be encoded on one or more non-transitory computer-readable media with instructions for one or more processors to cause steps to be performed. It is also noted that the non-transitory computer-readable media may include volatile and non-volatile memory. It is noted that alternative implementations are possible, including hardware and software/hardware implementations. Hardware-implemented functions may be realized using ASICs, programmable arrays, digital signal processing circuitry, and the like. Accordingly, the “means” terms in any claims are intended to cover both software and hardware implementations. Similarly, the term “computer-readable medium or media” as used herein includes software and/or hardware having a program of instructions embodied therein, or a combination thereof. With these implementation alternatives in mind, it is understood that the figures and accompanying description provide the functional information one skilled in the art would require to write program code (i.e., software) and/or to fabricate circuits (i.e., hardware) to perform the processing required. 
         [0057]    One skilled in the art will recognize that no particular protocol or programming language is critical to the practice of the present invention. One skilled in the art will also recognize that a number of the elements described above may be physically and/or functionally separated into sub-modules or combined together. 
         [0058]    It will be appreciated to those skilled in the art that the preceding examples and embodiments are exemplary and not limiting to the scope of the present invention. It is intended that all permutations, enhancements, equivalents, combinations, and improvements thereto that are apparent to those skilled in the art upon a reading of the specification and a study of the drawings are included within the true spirit and scope of the present invention.