# Patent

## Title
Protection switching over a virtual link aggregation

## Abstract

One embodiment of the present invention provides a switch. The switch comprises one or more ports and a link management module. The link management module operates a first aggregate link group as an active aggregate link group of a protected virtual link aggregation. This protected virtual link aggregation operates as a single logical channel. An aggregate link group comprises a plurality of logically aggregated links. The first aggregate link group, which represents the logical channel, comprises at least a first port of the one or more ports of the switch. The link management module also operates a second aggregate link group of the protected virtual link aggregation as a standby for the first aggregate link group. The second aggregate link group comprises at least a second port of the one or more ports of the switch. Forwarding is enabled via the first port and disabled via the second port.

## Background
RELATED APPLICATIONS
This application is a continuation application of application Ser. No. 14/151,693, titled “Protection Switching Over a Virtual Link Aggregation,” by inventors Prabu Thayalan and Ganesh D. Venkata, filed on 9 Jan. 2014, which claims the benefit of U.S. Provisional Application No. 61/751,808, titled “Protection Switching in Distributed Link Aggregation,” by inventors Prabu Thayalan and Ganesh D. Venkata, filed 11 Jan. 2013, the disclosures of which are incorporated by reference herein.
The present disclosure is related to U.S. patent application Ser. No. 13/087,239, titled “Virtual Cluster Switching,” by inventors Suresh Vobbilisetty and Dilip Chatwani, filed 14 Apr. 2011, and U.S. patent application Ser. No. 12/725,249, titled “Redundant Host Connection in a Routed Network,” by inventors Somesh Gupta, Anoop Ghanwani, Phanidhar Koganti, and Shunjia Yu, filed 16 Mar. 2010, the disclosures of which are incorporated by reference herein.


BACKGROUND
Field
The present disclosure relates to network management. More specifically, the present disclosure relates to a method and system for providing protection switching for virtual link aggregations (VLAGs).
Related Art
The exponential growth of the Internet has made it a popular delivery medium for multimedia applications, such as video on demand and television. Such applications have brought with them an increasing demand for bandwidth. As a result, equipment vendors race to build larger and faster switches with versatile capabilities, such as multicasting, to move more traffic efficiently. However, the size of a switch cannot grow infinitely. It is limited by physical space, power consumption, and design complexity, to name a few factors. Furthermore, switches with higher capability are usually more complex and expensive. More importantly, because an overly large and complex system often does not provide economy of scale, simply increasing the size and capability of a switch may prove economically unviable due to the increased per-port cost.
As more time-critical applications are being implemented in data communication networks, high-availability operation is becoming progressively more important as a value proposition for network architects. It is often desirable to aggregate links to multiple switches to operate as a single logical link (referred to as a virtual link aggregation or a multi-chassis trunk) to facilitate load balancing among the multiple switches while providing redundancy to ensure that a device failure or link failure would not affect the data flow. A switch participating in a virtual link aggregation can be referred to as a partner switch of the virtual link aggregation.
Currently, such virtual link aggregations in a network have not been able to take advantage of the protection switching available for a typical switch. Multiple switches in a network can operate in conjunction with each other to provide protection switching. Consequently, an end device coupled to multiple such switches can typically continue to exchanges data packets with one of the switches in the event of a failure (e.g., a link or a node failure). However, such failure leads to removal of learned information via the port associated with the failure. Hence, the switch needs to relearn all information again and the layer-2 spanning tree requires reconstruction. As a result, the switch is burdened with additional overhead.
While virtual link aggregation brings many desirable features to networks, some issues remain unsolved in efficient protection switching.
SUMMARY
One embodiment of the present invention provides a switch. The switch comprises one or more ports and a link management module. The link management module operates a first aggregate link group as an active aggregate link group of a protected virtual link aggregation. This protected virtual link aggregation operates as a single logical channel. An aggregate link group comprises a plurality of logically aggregated links. The first aggregate link group, which represents the logical channel, comprises at least a first port of the one or more ports of the switch. The link management module also operates a second aggregate link group of the protected virtual link aggregation as a standby for the first aggregate link group. The second aggregate link group comprises at least a second port of the one or more ports of the switch. Forwarding is enabled via the first port and disabled via the second port.
In a variation on this embodiment, a respective aggregate link group is a virtual link aggregation associated with the switch and a remote switch, wherein the virtual link aggregation operates as a single logical channel.
In a variation on this embodiment, the link management module determines the first aggregate link group as the active aggregate link group based on one or more of: (i) configuration of the first aggregate link group as the active aggregate link group, and (ii) dynamic selection of the first aggregate link group as the active aggregate link group based on a criteria.
In a variation on this embodiment, a respective aggregate link group comprises logically aggregated links coupled to a respective end device.
In a variation on this embodiment, forwarding is enabled via the first port based on one or more of: (i) setting the first port in a forwarding state, and (ii) setting the first port in an operationally up state. Forwarding is disabled via the second port based on one or more of: (i) setting the second port in a standby state, and (ii) setting the second port in an operationally down state.
In a variation on this embodiment, the switch also includes a protection switching module which detects an unavailability associated with the first aggregate link group based on an unavailability criterion. If the protection switching module detects the unavailability, the protection switching module enables forwarding via the second port. The second group starts representing the logical channel corresponding to the protected virtual link aggregation.
In a further variation, the unavailability criterion is based on one or more of: (i) minimum number of active link in a link aggregation group, and (ii) minimum aggregate bandwidth of a link aggregation group.
In a further variation, if the protection switching module detects a recovery from the unavailability, the protection switching module pre-empts traffic from the second port, enables forwarding via the first port, thereby enabling traffic forwarding via the first aggregate link group, and disables forwarding via the second port, thereby disabling traffic forwarding via the second aggregate link group.
In a further variation, if the protection switching module detects a recovery from the unavailability, the protection switching module continues forwarding via the second port, the second group continues to represent the logical channel corresponding to the protected virtual link aggregation, and operates the first aggregate link group as a standby for the second aggregate link group. Under such a scenario, forwarding is disabled via the first port.
In a variation on this embodiment, the switch is a member of an Ethernet fabric switch, which incorporates a plurality of physical switches coupled in an arbitrary topology logically operating as a single switch. The switch is associated with an identifier of the Ethernet fabric switch.



BRIEF DESCRIPTION OF THE FIGURES
FIG. 1A illustrates an exemplary protected virtual link aggregation comprising virtual link aggregations, in accordance with an embodiment of the present invention.
FIG. 1B illustrates an exemplary protected virtual link aggregation comprising link aggregations, in accordance with an embodiment of the present invention.
FIG. 2 presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation enabling an active group of the protected virtual link aggregation, in accordance with an embodiment of the present invention.
FIG. 3A presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation forwarding a frame via the protected virtual link aggregation, in accordance with an embodiment of the present invention.
FIG. 3B presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation forwarding a frame received via the protected virtual link aggregation, in accordance with an embodiment of the present invention.
FIG. 4 illustrates exemplary unavailability scenarios of a protected virtual link aggregation, in accordance with an embodiment of the present invention.
FIG. 5A presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation handling unavailability, in accordance with an embodiment of the present invention.
FIG. 5B presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation recovering from unavailability, in accordance with an embodiment of the present invention.
FIG. 6 illustrates an exemplary architecture of a switch with protected virtual link aggregation support, in accordance with an embodiment of the present invention.



In the figures, like reference numerals refer to the same figure elements.
DETAILED DESCRIPTION
The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the claims.
Overview
In embodiments of the present invention, the problem of providing efficient protection switching in a virtual link aggregation is solved by creating a protected virtual link aggregation comprising an active group and at least one other standby link aggregation group (can be referred to as groups). Links in the active group actively forward traffic via the virtual link aggregation, and the standby group(s) remain standby and can become active if the active group fails. A link in a virtual link aggregation can also be identified by a port associated with that link. In this disclosure, the terms “link” and “port” are used interchangeably to indicate participation in a virtual link aggregation.
Links in a virtual link aggregation form a single logical channel. With existing technologies, a respective link in a virtual link aggregation actively forwards traffic. In the virtual link aggregation, if a link or a switch becomes unavailable (e.g., due to a failure), the virtual link aggregation as a single logical channel can become unavailable. As a result, a respective partner switch of the virtual link aggregation needs to flush (i.e., remove) the information learned via the virtual link aggregation and relearn the flushed information again. Furthermore, if the partner switches are participating in a layer-2 spanning tree (e.g., based on Spanning Tree Protocol (STP), Rapid STP (RSTP), or Multiple STP (MSTP)) via the virtual link aggregation, the unavailability causes a respective partner switch need to reconstruct the spanning tree. As a result, the respective partner switches are burdened with additional overhead.
This problem can further aggravate if the partner switches are member switches of a fabric switch. In a fabric switch, any number of switches coupled in an arbitrary topology may logically operate as a single switch. To do so, the member switches of a fabric switch share learned information among each other. If a partner switch flushes information learned via the virtual link aggregation due to the unavailability, a respective member switch of the fabric switch also flushes that information. Furthermore, if the fabric switch supports layer-2 spanning tree, the fabric switch, as a single switch, may need to reconstruct the spanning tree. Consequently, a respective port of a respective member switch may need reconfiguration (e.g., determining whether the port is going to be in a forward state or a discarding state), which can lead to significant overhead in the fabric switch.
To solve this problem, a protected virtual link aggregation is formed comprising a plurality of link aggregation groups, each capable of meeting the requirements (e.g., bandwidth requirement) of the protected virtual link aggregation. In some embodiments, links of protected virtual link aggregation which are coupled to the same end device are logically aggregated to form a group. Among these groups, one group operates as the active group which forwards traffic via the protected virtual link aggregation and represent the logical channel corresponding to the protected virtual link aggregation. In some embodiments, only the active group actively represents the logical channel. Hence, the other groups operate as stand-by groups which do not forward traffic, thereby do not actively represent the logical channel.
However, a respective group is associated with the same protected virtual link aggregation (e.g., shares the same identifiers associated with the protected virtual link aggregation) and can individually (and mutually exclusively) represent the logical channel corresponding to the protected virtual link aggregation. In other words, a respective group individually can operate as if the group is representative of the logical channel corresponding to the protected virtual link aggregation. If the active group becomes unavailable, one of the standby groups starts operating as the active group, thereby representing the logical channel (e.g., using the same identifiers associated with the protected virtual link aggregation). As a result, other switches in the network may remain oblivious to the unavailability and the protected virtual link aggregation can continue to operate without triggering a learned information flush or spanning tree reconstruction in the network.
In some embodiments, the partner switches are member switches of a fabric switch. An end device can be coupled to the fabric switch via a virtual link aggregation. A fabric switch in the network can be an Ethernet fabric switch or a virtual cluster switch (VCS). In an Ethernet fabric switch, any number of switches coupled in an arbitrary topology may logically operate as a single switch. Any new switch may join or leave the fabric switch in “plug-and-play” mode without any manual configuration. In some embodiments, a respective switch in the Ethernet fabric switch is a Transparent Interconnection of Lots of Links (TRILL) routing bridge (RBridge). A fabric switch appears as a single logical switch to the end device.
A fabric switch runs a control plane with automatic configuration capabilities (such as the Fibre Channel control plane) over a conventional transport protocol, thereby allowing a number of switches to be inter-connected to form a single, scalable logical switch without requiring burdensome manual configuration. As a result, one can form a large-scale logical switch using a number of smaller physical switches. The automatic configuration capability provided by the control plane running on each physical switch allows any number of switches to be connected in an arbitrary topology without requiring tedious manual configuration of the ports and links. This feature makes it possible to use many smaller, inexpensive switches to construct a large fabric switch, which can be viewed and operated as a single switch (e.g., as a single Ethernet switch).
It should be noted that a fabric switch is not the same as conventional switch stacking. In switch stacking, multiple switches are interconnected at a common location (often within the same rack), based on a particular topology, and manually configured in a particular way. These stacked switches typically share a common address, e.g., IP address, so they can be addressed as a single switch externally. Furthermore, switch stacking requires a significant amount of manual configuration of the ports and inter-switch links. The need for manual configuration prohibits switch stacking from being a viable option in building a large-scale switching system. The topology restriction imposed by switch stacking also limits the number of switches that can be stacked. This is because it is very difficult, if not impossible, to design a stack topology that allows the overall switch bandwidth to scale adequately with the number of switch units.
In contrast, a fabric switch can include an arbitrary number of switches with individual addresses, can be based on an arbitrary topology, and does not require extensive manual configuration. The switches can reside in the same location, or be distributed over different locations. These features overcome the inherent limitations of switch stacking and make it possible to build a large “switch farm” which can be treated as a single, logical switch. Due to the automatic configuration capabilities of the fabric switch, an individual physical switch can dynamically join or leave the fabric switch without disrupting services to the rest of the network.
Furthermore, the automatic and dynamic configurability of fabric switch allows a network operator to build its switching system in a distributed and “pay-as-you-grow” fashion without sacrificing scalability. The fabric switch's ability to respond to changing network conditions makes it an ideal solution in a virtual computing environment, where network loads often change with time.
Although the present disclosure is presented using examples based on spanning tree protocols, embodiments of the present invention are not limited to spanning trees. Embodiments of the present invention are relevant to any networking technique which allows loop-less forwarding in a layer-2 network. In this disclosure, the term “spanning tree” is used in a generic sense, and can refer to any loop-free network topology.
The term “RBridge” refers to routing bridges, which are bridges implementing the TRILL protocol as described in Internet Engineering Task Force (IETF) Request for Comments (RFC) “Routing Bridges (RBridges): Base Protocol Specification,” available at http://tools.ietf.org/html/rfc6325, which is incorporated by reference herein. Embodiments of the present invention are not limited to application among RBridges. Other types of switches, routers, and forwarders can also be used.
In this disclosure, the term “end device” can refer to a physical or virtual host machine, a conventional switch, or any other type of network device. Additionally, an end device can be coupled to other switches or hosts further away from a network. An end device can also be an aggregation point for a number of switches to enter the network.
The term “switch identifier” refers to a group of bits that can be used to identify a switch. In a layer-2 communication, the switch identifier can be a media access control (MAC) address. If a switch is an RBridge, the switch identifier can be referred to as an “RBridge identifier.” Note that the TRILL standard uses “RBridge ID” to denote a 48-bit intermediate-system-to-intermediate-system (IS-IS) System ID assigned to an RBridge, and “RBridge nickname” to denote a 16-bit value that serves as an abbreviation for the “RBridge ID.” In this disclosure, “switch identifier” is used as a generic term and is not limited to any bit format, and can refer to any format that can identify a switch. The term “RBridge identifier” is also used in a generic sense and is not limited to any bit format, and can refer to “RBridge ID” or “RBridge nickname” or any other format that can identify an RBridge.
The term “frame” refers to a group of bits that can be transported together across a network. “Frame” should not be interpreted as limiting embodiments of the present invention to layer-2 networks. “Frame” can be replaced by other terminologies referring to a group of bits, such as “massage,” “packet,” “cell,” or “datagram.”
The term “switch” is used in a generic sense, and can refer to any standalone switch or switching fabric operating in any network layer. “Switch” should not be interpreted as limiting embodiments of the present invention to layer-2 networks. Any physical or virtual device (e.g., a virtual machine, which can be a virtual switch, operating on a computing device) that can forward traffic to an end device can be referred to as a “switch.” Examples of a “switch” include, but not limited to, a layer-2 switch, a layer-3 router, or a TRILL RBridge.
Network Architecture
FIG. 1A illustrates an exemplary protected virtual link aggregation comprising virtual link aggregations, in accordance with an embodiment of the present invention. As illustrated in FIG. 1A, switches 102 and 104 in network 100 are coupled to end devices 112 and 114 via a protected virtual link aggregation 120. Here, switches 102 and 104 are partner switches of protected virtual link aggregation 120. In some embodiments, links in protected virtual link aggregation 120, which are coupled to an end device, are considered as a group. Protected virtual link aggregation 120 includes link aggregation group 122, which includes links to end device 112, and link aggregation group 124, which includes links to end device 114. In this example, groups 122 and 124, respectively, are virtual link aggregations, and couple end devices 112 and 114, respectively, with both switches 102 and 104.
In some embodiments, network 100 is a fabric switch, and switches 102, 104, and 106 are member switches of the fabric switch. In some further embodiments, a respective switch in the fabric switch is a TRILL RBridge. The fabric switch of network 100 appears as a single logical switch to end devices 112 and 114. The fabric switch of network 100 runs a control plane with automatic configuration capabilities (such as the Fibre Channel control plane) over a conventional transport protocol, thereby allowing a number of switches to be inter-connected to form a single, scalable switch without requiring burdensome manual configuration. As a result, network 100 can form a large-scale switch using a number of smaller physical switches (e.g., switches 102, 104, and 106).
Each of groups 122 and 124 are configured to operate in a special “trunked” mode for end devices 112 and 114. End devices 112 and 114 view switches 102 and 104 as a common virtual switch 110, with a corresponding virtual switch identifier. Dual-homed end devices 112 and 114, which are coupled to more than one switches, are considered to be logically coupled to virtual switch 110 via logical links represented by dotted lines. Virtual switch 110 is considered to be logically coupled to both switches 102 and 104, optionally with zero-cost links (also represented by dotted lines). Incoming frames from end devices 112 and 114 are marked with virtual switch 110's identifier as their ingress switch identifier. As a result, other switches in network 100 learn that end devices 112 and 114 are both reachable via virtual switch 110. Furthermore, switches 102 and 104 can advertise their respective connectivity (optionally via zero-cost links) to virtual switch 110. Hence, multi-pathing can be achieved when other switches, such as switch 106, choose to send frames to virtual switch 110 (which are marked as the egress switch in the frames) via switches 102 and 104.
Since the two partner switches function as a single logical switch, the MAC address reachability learned by a respective partner switch is shared with the other partner switch. For example, during normal operation, end device 112 may choose to send its outgoing frames only via the link to switch 102. As a result, only switch 102 would learn end device 112's MAC address (and the corresponding port on switch 102 to which end station 112 is coupled). Switch 102 then shares this information with switch 104. Since the frames coming from end device 112 would have virtual switch 110's identifier as their ingress switch identifier, when other devices in the network send frames back to end device 112, these frames would have virtual switch 110's identifier as their egress switch identifier, and these frames might be sent to either switch 102 or 104. When switch 104 receives such a frame, it can determine that this frame can either be sent to locally coupled end device 112 or partner switch 102, based on the MAC reachability information shared by switch 102.
Links in groups 122 and 124 are configured as a single protected virtual link aggregation 120. In some embodiments, the protection switching feature should be enabled for protected virtual link aggregation 120. Otherwise, protected virtual link aggregation 120 can operate as a regular virtual link aggregation (e.g., with the protection switching feature disabled). It should be noted that virtual switch 110 is associated with a respective group in protected virtual link aggregation 120. In other words, both dual-homed end devices 112 and 114 can share the same virtual switch 110 for groups 122 and 124, respectively. As a result, frames from both end devices 112 and 114 are marked with virtual switch 110's identifier. This feature makes the present solution scalable, because when one of the groups is unavailable, the other group can continue the operations of protected virtual link aggregation 120. As a result, switch 106 can remain oblivious to the unavailability, and protected virtual link aggregation 120 can continue to operate without triggering information relearning or spanning tree reconstruction (e.g., based on Spanning Tree Protocol (STP), Rapid STP (RSTP), or Multiple STP (MSTP)) in network 100.
In addition, an end device is not required to change the way it is configured for a link aggregation. A dual-homed end device only needs to be configured to have an aggregate link to the virtual switch, as would be the case with a conventional, physical switch, using an existing link aggregation method. Hence, the dual-homed end device does not need to be aware that the virtual switch on the other end of the aggregate link is actually two physical switches. Furthermore, the rest of network 100 (apart from switches 102 and 104) is also not required to be aware that virtual switch 110 is actually not a physical switch. For example, to switch 106, virtual switch 110 can be indistinguishable from any of the physical switches. Therefore, the present invention does not require extra configuration to the rest of network 100.
When two end devices, such as end devices 112 and 114, are coupled to each other, these end devices can form a loop with network 100 via protected virtual link aggregation 120. As a result, end devices 112 and 114 can be considered as redundantly connected with network 100. A respective group separately couples network 100 with one of the redundant end devices. For example, group 122 couples end device 112 and group 124 couples end device 114 with network 100 via protected virtual link aggregation 120. One group operates as the primary or active group, and the other group(s) act as secondary or standby group(s).
Suppose that groups 122 and 124 are active and standby groups, respectively. Consequently, group 122 actively represents the logical channel corresponding to virtual link aggregation 120. In some embodiments, the active group exclusively represents the logical channel. During normal operation, forwarding via the ports participating in group 122 is enabled and via the ports participating in group 124 is logically disabled. Group 122 then carries traffic for protected virtual link aggregation 120 only from end device 112. For example, incoming frames from end device 112 via group 122 are marked with virtual switch 110's identifier as their ingress switch identifier.
In some embodiments, switches 102 and 104 are only aware of end device 112, which is coupled to network 100 via active group 122, among the redundant end device 112 and 114. If active group 122 becomes unavailable (e.g., due to a failure), protection switching is triggered, and standby group 124 takes over and starts forwarding traffic for protected virtual link aggregation 120. As a result, switches 102 and 104 automatically starts receiving traffic from the other redundant end device 114. In this way, group 124 becomes the new active group and continues traffic forwarding via protected virtual link aggregation 120. This allows protected virtual link aggregation 120 to continue to operate as the same logical channel. For example, upon becoming active, group 124 operates as if group 124 incoming frames from end device 114 via group 124 are marked with virtual switch 110's identifier as their ingress switch identifier.
Moreover, when active group 122 becomes unavailable during the protection switching, the status of protected virtual link aggregation 120 does not flap (e.g., protected virtual link aggregation 120 as a logical channel remain available). This precludes partner switches 102 and 104 from reprogramming the protocol configurations associated with protected virtual link aggregation 120. In other words, partner switches 102 and 104 can retain the protocol configurations associated with protected virtual link aggregation 120. For example, during the protection switching, layer-2/layer-3 information obtained via protected virtual link aggregation 120 are not flushed and relearned. This leads to a fast re-convergence after a protection switchover. Examples of such information include, but are not limited to, MAC address, which can be learned from layer-2 header processing, and/or multicast group association, which can be learned from Internet Group Management Protocol (IGMP) or Multicast Listener Discovery (MLD) snooping, of an end device.
In some embodiments, an active group can be configured (e.g., statically configured) by a user (e.g., a network administrator) for protected virtual link aggregation 120. This configuration allows the user to determine the links which carry traffic. Other group(s) of protected virtual link aggregation 120 operate as standby group(s). Links participating in the standby group(s) in partner switches 102 and 104 are maintained in an “operationally down” state. A link in the “operationally down” state operates as if the link is unplugged. As a result, the link is precluded from forwarding traffic. If protection switching is needed, links participating in the standby group(s) in partner switches 102 and 104 are switched to an “operationally up” state, wherein a link in the “operationally up” state operates as if the link is plugged and can forward traffic.
If an active group is not configured protected virtual link aggregation 120, one of groups 122 and 124 is dynamically selected as the active group based on a criterion. In some embodiments, the criterion indicates that the first group configured for protected virtual link aggregation 120 is dynamically selected as the active group. For example, if group 122 is configured before group 124 for protected virtual link aggregation 120, group 122 is dynamically selected as the active group. Links participating in the standby group(s) are maintained in a “standby” state (e.g., a multiplexer machine state indicating that the corresponding link is in a standby state). If a protection switching is needed, links participating in the standby group(s) can be rapidly switched to a “forwarding” state (e.g., a multiplexer machine state indicating that the corresponding link is in a collecting & distributing state).
In some embodiments, if group 122 is configured as the active group for protected virtual link aggregation 120, whenever group 122 is operating, traffic forwarding via group 124 is pre-empted. For example, if active group 122 is unavailable due to a failure, group 124 becomes active and starts forwarding traffic. When group 122 recovers from the failure and becomes available, traffic is reverted to group 122 from currently active group 124. Group 124 is then switched to being a standby group. On the other hand, in some embodiments, if group 122 is dynamically selected as the active group for protected virtual link aggregation 120, group 122 may not pre-empt traffic forwarding. For example, if dynamically selected active group 122 is unavailable due to a failure, group 124 becomes active and starts forwarding traffic. When group 122 recovers from the failure and becomes available, switches 102 and 104 continue to forward traffic via currently active group 124. After being available, group 122 becomes a standby group.
In some embodiments, protection switching can be triggered for protected virtual link aggregation 120 based on one or more criteria. Examples of such a criterion include, but are not limited to, minimum aggregate bandwidth and minimum number of active links. For example, if minimum number of active links is the criterion for triggering protection switching, a minimum number of active links is needed for group 122 or 124 to be the active group. Suppose that group 122 is the active group and the minimum number of active links is two. If at any point of time, group 122 does not have two active links (e.g., due to a link failure), the protection switching is triggered, and group 124 becomes the active group. This provides flexibility to a user to determine one or more criteria for triggering the protecting switching.
FIG. 1B illustrates an exemplary protected virtual link aggregation comprising link aggregations, in accordance with an embodiment of the present invention. In the example in FIG. 1B, switches 102 and 104 in network 100 are coupled to end devices 112 and 114 via protected virtual link aggregation 130. Here, switches 102 and 104 are partner switches of protected virtual link aggregation 130. Because links in protected virtual link aggregation 130, which are coupled to an end device, are considered as a group, the link aggregation between switch 102 and end device 112 forms a link aggregation group 132, and the link aggregation between switch 104 and end device 114 forms a link aggregation group 134.
As described in conjunction with FIG. 1A, one of groups 132 and 134 operates as the active group and the other group operates as the standby group. When the active group becomes unavailable, the standby group starts operating as the active group. This allows partner switches 102 and 104 to retain the protocol configurations associated with protected virtual link aggregation 130. For example, during the protection switching, layer-2/layer-3 information obtained via protected virtual link aggregation 130 are not flushed and relearned. Hence, a protected virtual link aggregation can be constructed based on link aggregations between individual switches and redundant end devices, without requiring the end device to have a virtual link aggregation with a plurality of switches.
Enabling a Protected Virtual Link Aggregation
In the example in FIG. 1A, protected virtual link aggregation 120 is formed by incorporating link aggregation groups 122 and 124 coupled to redundant end devices 112 and 114, respectively. Among groups 122 and 124, one is selected as the active group, which is responsible for forwarding traffic via protected virtual link aggregation 120, and the other is selected as the standby group. An active group can be configured, or dynamically selected.
FIG. 2 presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation enabling an active group of the protected virtual link aggregation, in accordance with an embodiment of the present invention. During operation, the switch detects a protected virtual link aggregation associated with the local switch (operation 202). In some embodiments, a user configures the protected virtual link aggregation for the switch, which, in turn, detects the protected virtual link aggregation based on the configuration. The switch then checks whether an active group is configured (operation 204). If so, the switch enables forwarding via the local ports (i.e., ports in the switch) participating in the active group by setting the corresponding local ports in an operationally up state (operation 206). The switch sets the local ports participating in the standby group(s) (e.g., groups other than the active group) in an operationally down state (operation 208).
If an active group is not configured for the protected virtual link aggregation, the active group is dynamically selected. The switch then identifies the link aggregation groups in the protected virtual link aggregation (operation 212). The switch determines the active group from the identified group based on a criterion (operation 214). In some embodiments, the criterion indicates that the group first configured in the protected virtual link aggregation is selected as the active group. The switch then enables forwarding via the local ports participating in the active group by setting the corresponding local ports in a forwarding state (e.g., a multiplexer machine state indicating that the corresponding links are in a collecting & distributing state) (operation 216). The switch sets the local ports participating in the standby group(s) in a standby state (e.g., a multiplexer machine state indicating that the corresponding links are in a standby state) (operation 218).
Forwarding Via a Protected Virtual Link Aggregation
FIG. 3A presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation forwarding a frame via the protected virtual link aggregation, in accordance with an embodiment of the present invention. During operation, the switch receives a frame to be forwarded via the protected virtual link aggregation (operation 302) and checks whether the destination is coupled to an active group (operation 304). In the example in FIG. 1A, such a frame can be received by partner switch 102 from switch 106. If group 122 is the active group, switch 102 checks whether the destination is coupled to group 122 (e.g., destination is reachable via group 122).
If the destination is coupled to the active group, the switch identifies the local active ports (e.g., ports in a “forwarding” or “operationally up” state, as described in conjunction with FIG. 1A) participating in the active group (operation 306). The switch determines an egress port for the frame among the identified ports (operation 308) and forwards the frame via the determined egress port (operation 310). If the destination is not coupled to the active group (e.g., coupled to a standby group), the switch precludes the local switch from forwarding the frame via the protected virtual link aggregation (operation 312). In the example of FIG. 1A, if group 122 is the active group and the destination of such a frame is coupled to group 124, switch 102 or 104 precludes itself from forwarding the frame via protected virtual link aggregation 120. In some embodiments, such a frame can be dropped.
FIG. 3B presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation forwarding a frame received via the protected virtual link aggregation, in accordance with an embodiment of the present invention. During operation, the switch receives a frame from an end device via a local port participating in the protected virtual link aggregation (operation 352) and checks whether the local port(s) are active (operation 354). If the local port is not active (e.g., the port is in a “standby” or “operationally down” state, as described in conjunction with FIG. 1A), the switch discards (i.e., drops) the received frame (operation 370). Note that the switch can drop the frame at the ingress port.
If the local port is active, the switch checks whether the information associated with the frame has already been learned (operation 356). For example, the switch checks whether the source MAC address of the frame has been learned. Even though some information associated with the frame can already be learned, some other information may not be learned. For example, if the frame includes an IGMP join message, layer-2 information, such as the source MAC address, of the frame may already be learned, but layer-3 information, such as the multicast group association, may not be learned. If any information associated with the frame is not learned, the switch learns the corresponding layer-2/layer-3 information from the frame (operation 358), and then constructs a notification message comprising the learned information and forwards the notification message to the partner switches (operation 360). In some embodiments, the notification message is a name service message of a fabric switch. This notification message can be encapsulated in a TRILL header.
If information associated with the frame has already been learned (operation 356) or the notification message has been forwarded to partner switches (operation 360), the switch encapsulates the frame and includes an egress switch identifier in the encapsulation header based on the frame's destination information (operation 362). In some embodiments, the switch encapsulates the frame in a TRILL packet, and includes an RBridge identifier as the egress switch identifier in the TRILL header. The switch then identifies an egress port based on the egress switch identifier (operation 364) and forwards the frame via the identified egress port (operation 366). If the frame is encapsulated in a TRILL header, the identified egress port can correspond to an egress RBridge.
Protection Switching
Network scenarios often change, leading to unavailability of links and nodes in the network. A port of a switch can fail or a switch can be taken off of a network because of maintenance. During such unavailability, the protected virtual link aggregation can provide protection switching and continue to operate without triggering a learned information flush or spanning tree reconstruction. FIG. 4 illustrates exemplary unavailability scenarios of a protected virtual link aggregation, in accordance with an embodiment of the present invention. During operation, group 122 becomes the active group (based on either configuration or dynamic selection). As a result, partner switches 102 and 104 forward traffic via the links (i.e., ports) participating in group 122 and preclude themselves from forwarding via the links participating in group 124.
Suppose that link 410 between switch 102 and end device 112 becomes unavailable due to failure 402. If the criterion for triggering protection switching is the minimum number of active links and the minimum number is two, group 122 no longer meets the criterion due to the unavailability of link 410. As a result, protection switching for protected virtual link aggregation 120 is triggered. Similarly, if switch 102 becomes unavailable due to failure 404, link 410 becomes unavailable, and protection switching for protected virtual link aggregation 120 is triggered.
As a result, standby group 124 takes over as the active group and starts representing the logical channel corresponding to protected virtual link aggregation 120. Group 124 then starts forwarding traffic for protected virtual link aggregation 120. This allows group 124 to continue to represent the logical channel corresponding to protected virtual link aggregation 120. For example, upon becoming active, incoming frames from end device 114 via group 124 are marked with virtual switch 110's identifier as their ingress switch identifier. As a result, even during failure 402 or 404, switch 106 can remain oblivious to the failure, and protected virtual link aggregation 120 can continue to operate without triggering a learned information flush or spanning tree reconstruction in network 100.
In some embodiments, if group 122 is configured as the active group for protected virtual link aggregation 120, group 122 can pre-empt traffic forwarding via group 124. For example, when link 410 or switch 102 recovers from failure 402 or 404, respectively, group 122 becomes available. Traffic is then reverted to group 122 from currently active group 124, which is switched to being a standby group. On the other hand, in some embodiments, if group 122 is dynamically selected as the active group for protected virtual link aggregation 120, group 122 may not pre-empt traffic forwarding. For example, when link 410 or switch 102 recovers from failure 402 or 404, respectively, group 122 becomes available. However, switches 102 and 104 continue to forward traffic via currently active group 124. After being available, group 122 becomes a standby group.
FIG. 5A presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation handling unavailability, in accordance with an embodiment of the present invention. During operation, the switch detects an unavailability associated with a protected virtual link aggregation (operation 502) and checks whether the unavailability is associated with the active group (operation 504). If the unavailability is associated with the active group, the switch checks whether the unavailability has triggered the protection switching criterion (operation 506), as described in conjunction with FIG. 4. Examples of the criterion include, but are not limited to, minimum aggregate bandwidth and minimum number of active links. If the unavailability is not associated with the active group (operation 504) or the criterion has not been triggered (operation 506), the switch continues forwarding traffic via local port(s) belonging to the active group (operation 512).
If the unavailability has triggered the protection switching criteria, the switch identifies the candidate group among standby group(s) of the protected virtual link aggregation (operation 508). This candidate group is next in line among the standby groups for becoming the active group. The switch then activates forwarding via the local ports participating in the candidate group, which starts representing the logical channel corresponding to the protected virtual link aggregation (operation 510). In some embodiments, enabling forwarding entails setting the ports in a “forwarding” or “operationally up” state, as described in conjunction with FIG. 1A. As a result, other switches of the network can remain oblivious to the unavailability and the protected virtual link aggregation can continue to operate.
FIG. 5B presents a flowchart illustrating the process of a partner switch of a protected virtual link aggregation recovering from unavailability, in accordance with an embodiment of the present invention. During operation, the switch detects recovery from unavailability associated with previously active group of the protected virtual link aggregation (operation 552) and checks whether the previous active group is a configured active group (operation 554). If the previous active group is not a configured active group (e.g., a dynamically selected active group), the switch continues forwarding via the local ports participating in the current active group (operation 562) and operates the previous active group as a standby group (operation 564), as described in conjunction with FIG. 2. In some embodiments, operating the previous active group as a standby group entails setting the ports of the previous active group in a “standby” state, as described in conjunction with FIG. 1A.
If the previous active group is a configured active group, the switch pre-empts traffic forwarding via the local ports participating in the current active group (operation 556). The switch then activates forwarding via the local ports participating in the previous active group of the protected virtual link aggregation (operation 558). In some embodiments, enabling forwarding entails setting the ports in an “operationally up” state, as described in conjunction with FIG. 1A. The switch then operates the current active group as a standby group of the protected virtual link aggregation (operation 560), as described in conjunction with FIG. 2. In some embodiments, operating the current active group as a standby group entails setting the ports of the current active group in an “operationally down” state, as described in conjunction with FIG. 1A.
Exemplary Switch
FIG. 6 illustrates an exemplary architecture of a switch with protected virtual link aggregation support, in accordance with an embodiment of the present invention. In this example, a switch 600 includes a number of communication ports 602, a packet processor 610, a link management module 640, and a storage device 650. Packet processor 610 extracts and processes header information from the received frames.
In some embodiments, switch 600 may maintain a membership in a fabric switch, wherein switch 600 also includes a fabric switch management module 660. Fabric switch management module 660 maintains a configuration database in storage device 650 that maintains the configuration state of every switch within the fabric switch. Fabric switch management module 660 maintains the state of the fabric switch, which is used to join other switches. In some embodiments, switch 600 can be configured to operate in conjunction with a remote switch as an Ethernet switch. Under such a scenario, communication ports 602 can include inter-switch communication channels for communication within a fabric switch. This inter-switch communication channel can be implemented via a regular communication port and based on any open or proprietary format. Communication ports 602 can include one or more TRILL ports capable of receiving frames encapsulated in a TRILL header. Packet processor 610 can process these TRILL-encapsulated frames.
During operation, link management module 640 operates a first group of a protected virtual link aggregation as an active group. The first group comprises at least a first port of communication ports 602. Link management module 640 also operates a second group of the protected virtual link aggregation as the standby for the first group. The second group comprises at least a second port of communication ports 602. Forwarding is enabled via the first port and disabled via the second port. Link management module 640 can determine the first group as the active group based configuration and/or dynamic selection, as described in conjunction with FIG. 2. In some embodiments, link management module 640 operates the first and the second groups as virtual link aggregations in conjunction with a remote switch.
In some embodiments, switch 600 also includes a protection switching module 630, which detects an unavailability associated with the first group based on an unavailability criterion. The unavailability criterion is based on minimum number of active links and/or minimum aggregate bandwidth of a group. Upon detecting the unavailability, protection switching module 630 enables forwarding via the second port. Consequently, the second group starts representing the logical channel corresponding to the protected virtual link aggregation, as described in conjunction with FIG. 5A. Upon detecting a recovery from the unavailability, protection switching module 630 either continues to operate the second group as the active group or reverts back to the first group as the active group, as described in conjunction with FIG. 5B.
Note that the above-mentioned modules can be implemented in hardware as well as in software. In one embodiment, these modules can be embodied in computer-executable instructions stored in a memory which is coupled to one or more processors in switch 600. When executed, these instructions cause the processor(s) to perform the aforementioned functions.
In summary, embodiments of the present invention provide a switch, a method and a system for protection switching over a virtual link aggregation. In one embodiment, the switch comprises one or more ports and a link management module. The link management module operates a first aggregate link group as an active aggregate link group of a protected virtual link aggregation. This protected virtual link aggregation operates as a single logical channel. An aggregate link group comprises a plurality of logically aggregated links. The first aggregate link group, which represents the logical channel, comprises at least a first port of the one or more ports of the switch. The link management module also operates a second aggregate link group of the protected virtual link aggregation as a standby for the first aggregate link group. The second aggregate link group comprises at least a second port of the one or more ports of the switch. Forwarding is enabled via the first port and disabled via the second port.
The methods and processes described herein can be embodied as code and/or data, which can be stored in a computer-readable non-transitory storage medium. When a computer system reads and executes the code and/or data stored on the computer-readable non-transitory storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the medium.
The methods and processes described herein can be executed by and/or included in hardware modules or apparatus. These modules or apparatus may include, but are not limited to, an application-specific integrated circuit (ASIC) chip, a field-programmable gate array (FPGA), a dedicated or shared processor that executes a particular software module or a piece of code at a particular time, and/or other programmable-logic devices now known or later developed. When the hardware modules or apparatus are activated, they perform the methods and processes included within them.
The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit this disclosure. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. The scope of the present invention is defined by the appended claims.

## Claims

1. A switch, comprising:
link management circuitry configured to:
operate a protected virtual link aggregation group comprising a first and a second aggregate link groups as a protected logical channel, and wherein an aggregate link group comprises a plurality of aggregated links operating as a logical channel;
operate the first aggregate link group as an active logical channel representing the protected logical channel; and
operate the second aggregate link group as a standby logical channel in the protected virtual link aggregation group; and

forwarding circuitry configured to:
encapsulate a packet received via the protected virtual link aggregation with an encapsulation header; and
assign a virtual switch identifier as an ingress identifier of the encapsulation header, wherein the virtual switch identifier is associated with the first and the second aggregate link groups.

2. The switch of claim 1, further comprising protection switching circuitry configured to, in response to detecting an unavailability of the first aggregate link group, operate the second aggregate link group as an active logical channel representing the protected logical channel; and
wherein the forwarding circuitry is further configured to:
encapsulate a second packet received via the protected virtual link aggregation with a second encapsulation header; and
assign the virtual switch identifier as an ingress identifier of the second encapsulation header.

3. The switch of claim 2, wherein the protection switching circuitry is configured to detect the unavailability of the first aggregate link group based on one or more of:
minimum number of active link in the first link aggregation group; and
minimum aggregate bandwidth of the first link aggregation group.

4. The switch of claim 2, wherein the protection switching circuitry is further configured to, in response to detecting an unavailability of the first aggregate link group, preclude the switch from triggering a learned information flush or a spanning tree reconstruction associated with the first aggregate link group.

5. The switch of claim 1, wherein the forwarding circuitry is further configured to decapculate a second encapsulation header of a second packet in response to detecting the virtual switch identifier as an egress identifier of the second encapsulation header.

6. The switch of claim 1, wherein the first and the second aggregate link groups are virtual link aggregation groups coupling the switch and a remote switch to respective end devices.

7. The switch of claim 6, wherein the link management circuitry is further configured to construct a notification message comprising a MAC address learned from a local port participating in the first aggregate link group, wherein the notification message is destined for the remote switch.

8. A method, comprising:
operating a protected virtual link aggregation group comprising a first and a second aggregate link groups as a protected logical channel, wherein an aggregate link group comprises a plurality of aggregated links operating as a logical channel;
operating the first aggregate link group as an active logical channel representing the protected logical channel; and
operating the second aggregate link group as a standby logical channel in the protected virtual link aggregation group;
encapsulating a packet received via the protected virtual link aggregation with an encapsulation header; and
assigning a virtual switch identifier as an ingress identifier of the encapsulation header, wherein the virtual switch identifier is associated with the first and the second aggregate link groups.

9. The method of claim 8, in response to detecting an unavailability of the first aggregate link group, further comprising:
operating the second aggregate link group as an active logical channel representing the protected logical channel;
encapsulating a second packet received via the protected virtual link aggregation with a second encapsulation header; and
assigning the virtual switch identifier as an ingress identifier of the second encapsulation header.

10. The method of claim 9, further comprising detecting the unavailability of the first aggregate link group based on one or more of:
minimum number of active link in the first link aggregation group; and
minimum aggregate bandwidth of the first link aggregation group.

11. The method of claim 9, further comprising, in response to detecting an unavailability of the first aggregate link group, precluding a switch participating in the protected virtual link aggregation group from triggering a learned information flush or a spanning tree reconstruction associated with the first aggregate link group.

12. The method of claim 8, further comprising decapculating a second encapsulation header of a second packet in response to detecting the virtual switch identifier as an egress identifier of the second encapsulation header.

13. The method of claim 8, wherein the first and the second aggregate link groups are virtual link aggregation groups coupling a first switch and a second switch to respective end devices.

14. The method of claim 13, further comprising constructing a notification message comprising a MAC address learned from a local port of the first switch, wherein the local port participates in the first aggregate link group, and wherein the notification message is destined for the second switch.

15. A computing system, comprising:
a processor;
a memory storing instructions that when executed by the processor cause the system to perform a method, the method comprising:
operating a protected virtual link aggregation group comprising a first and a second aggregate link groups as a protected logical channel, wherein an aggregate link group comprises a plurality of aggregated links operating as a logical channel;
operating the first aggregate link group as an active logical channel representing the protected logical channel; and
operating the second aggregate link group as a standby logical channel in the protected virtual link aggregation group;
encapsulating a packet received via the protected virtual link aggregation with an encapsulation header; and
assigning a virtual switch identifier as an ingress identifier of the encapsulation header, wherein the virtual switch identifier is associated with the first and the second aggregate link groups.

16. The computing system of claim 15, wherein, in response to detecting an unavailability of the first aggregate link group, the method further comprises:
operating the second aggregate link group as an active logical channel representing the protected logical channel;
encapsulating a second packet received via the protected virtual link aggregation with a second encapsulation header; and
assigning the virtual switch identifier as an ingress identifier of the second encapsulation header.

17. The computing system of claim 16, wherein, in response to detecting an unavailability of the first aggregate link group, the method further comprises precluding a switch participating in the protected virtual link aggregation group from triggering a learned information flush or a spanning tree reconstruction associated with the first aggregate link group.

18. The computing system of claim 15, wherein the method further comprises decapculating a second encapsulation header of a second packet in response to detecting the virtual switch identifier as an egress identifier of the second encapsulation header.

19. The computing system of claim 15, wherein the first and the second aggregate link groups are virtual link aggregation groups coupling a the computing system and a remote computing system to respective end devices.

20. The computing system of claim 19, wherein the method further comprises constructing a notification message comprising a MAC address learned from a local port participating in the first aggregate link group, and wherein the notification message is destined for the remote computing system.