Redundant link management switch for use in a stack of switches and method thereof

CROSS-REFERENCE TO RELATED APPLICATION

P-0001[0001] This application is a continuation-in-part of copending application Ser. No. 10/041,505, filed Jan. 10, 2002.

BACKGROUND OF THE INVENTION

P-0002[0002] 1. Field of the Invention

P-0003[0003] The invention relates to computer networks, and more particularly to a stackable switch offering resilient stacking and backup management.

P-0004[0004] 2. Description of the Related Art

P-0005[0005] A typical computer network consists of nodes (computers), a connecting medium (wired or wireless), and specialized network equipment like routers and hubs. In the case of the Internet, all these pieces working together allow one computer to send information to another computer that may be on the other side of the world. Switches are a fundamental part of most networks. They make it possible for several users to send information over a network at the same time without slowing each other down. Just like routers allow different networks to communicate with each other, switches allow different nodes of a network to communicate directly with each other in a smooth and efficient manner.

P-0006[0006] The use of stackable switches allows network administrators to build systems having multiple physical ports to various computing resources or workstations on the network. FIG. 1 illustrates a stack of switches that can be constructed by stacking switches <b>110</b><i>a˜d. </i>To enable the stackable capability of each switch, the switches <b>110</b><i>a˜d </i>are respectively equipped with stacking modules <b>112</b><i>a˜d </i>as depicted. The stacking module <b>112</b><i>a </i>of the switch <b>110</b><i>a </i>is connected to stacking module <b>112</b><i>b </i>of the switch <b>110</b><i>b </i>with link <b>120</b><i>a, </i>and the stacking module <b>112</b><i>b </i>of the switch <b>110</b><i>b </i>is connected to stacking module <b>112</b><i>c </i>of the switch <b>110</b><i>c </i>with link <b>120</b><i>b. </i>Likewise, link <b>120</b><i>c </i>connects the switches <b>110</b><i>c </i>and <b>110</b><i>d. </i>The benefits of stacking are throughput boost, downlink resource sharing, and easy management. The switch stack <b>100</b> delivers high-performance switch-to-switch connections, while conserving ports. Network administrators may manage the entire switch stack <b>100</b> as one virtual switch.

P-0007[0007] However, the entire switch stack <b>100</b> is disrupted in the case of single link or single switch failure anywhere in the stack <b>100</b>. Since the switch stack <b>100</b> is arranged as a simple chain, as shown in FIG. 1, without a redundant link, the rest of the switches cannot be stacked together until the network administrator manually solves the problems. To make matters worse, the switch stack with only a single management module can prevent either the entire network or a substantial portion of the network from functioning when a failure only occurs in the single management module.

P-0008[0008] Therefore, what is needed is a way to automatically recover a switch stack in case of switch or link failure, unencumbered by the limitations associated with the prior art.

SUMMARY OF THE INVENTION

P-0009[0009] It is an object of the present invention to provide a redundant link for a stack of switches within a network.

P-0010[0010] It is another object of the present invention to provide a mechanism to detect a failed link within a stack of switches forming a closed-loop link topology.

P-0011[0011] It is yet another object of the present invention to provide a mechanism to establish backup management in a stack of switches arranged in a closed-loop link topology, which features the inheritable master role to ease management.

P-0012[0012] The present invention is generally directed to a redundant link management switch for use in a stack of switches forming a closed-loop link topology. The redundant link management switch includes a stacking module, a processor and a management module. The stacking module has an uplink port and a downlink port. The uplink port connects a next-higher switch in the stack, and the downlink port connects a next-lower switch in the stack, in which a link connecting the downlink port and the next-lower switch is a redundant link for the switch stack. The processor instructs the stacking module to disable a downlink control bus within the downlink port when receiving a disconnect command, and instructs the stacking module to enable the downlink control bus when receiving a reconnect command. The processor also provides a link status. The management module performs a redundant link management function, issuing the disconnect command to the processor if the link status indicates that the redundant link management switch and the stack of switches are stacked into the closed-loop link topology. Conversely, the management module issues the reconnect command to the processor to recover the redundant link if the management module detects that the closed-loop link topology has changed. Preferably, a manual control device is disposed on the stacking module. The redundant link management function is enabled when the management module detects that the manual control device has activated. Once the manual control device on the stacking module is activated, the management module in the same switch as the stacking module has the highest priority to become a master agent for the stack of switches.

P-0013[0013] In another aspect of the invention, a method of managing a redundant link for use in a stack of switches is disclosed. First, every two switches in the switch stack are connected via links including the redundant link to form a closed-loop link topology. A link status is then detected and the redundant link is deactivated if the link status indicates that the switch stack forms the closed-loop link topology. Each of the switches is polled through the links within the switch stack. If one of the switches in the switch stack fails to respond to the polling, the redundant link in the switch stack is activated. Thereafter, the switches are re-initialized to form a new switch stack in which the redundant link is activated. After re-initialization, unit IDs should be reassigned to respective switches in the new switch stack. It is also required to determine whether the new switch stack has changed from the closed-loop link topology to another link topology. If the closed-loop link topology has changed, a link connected between one switch with the lowest unit ID and another switch with the highest unit ID is identified as a disconnected link.

P-0014[0014] In yet another aspect of the invention, there is provided a method for establishing backup management in a stack of switches arranged in a closed-loop link topology. The switches in the stack include a first switch equipped with a first management module and a second switch equipped with a second management module. To begin with, a manual control device of the first switch is activated and so a link attached to a downlink port of the first switch is treated as a redundant link. The redundant link is then deactivated. Next, unit IDs are assigned to respective switches in the switch stack, wherein the first switch is assigned to a particular unit ID. According to arbitration between the management modules, the first management module in the first switch with the dedicated unit ID is determined to be a master agent for the switch stack and the second management module is determined to serve as a backup agent for the switch stack. After that, the first management module synchronizes data with the second management module. If the closed-loop link topology is changed, the redundant link is activated responsively. The switches are re-initialized to form a new switch stack in which the redundant link is activated. Once the manual control device of the first switch is activated, the first management module in the first switch has the highest priority to become the master agent for the new switch stack after re-initialization. Thus, the first management module is enabled to inherit the master role.

DESCRIPTION OF THE DRAWINGS

P-0015[0015] The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:

P-0016[0016]FIG. 1 illustrates stacking of switches;

P-0017[0017]FIG. 2A is a stack of switches forming a closed-loop link topology in accordance with the invention;

P-0018[0018]FIG. 2B illustrates one stacking recovery example in accordance with the invention;

P-0019[0019]FIG. 2C illustrates another stacking recovery example in accordance with the invention;

P-0020[0020]FIG. 2D is a stack of switches forming the closed-loop link topology as an illustration of backup management;

P-0021[0021]FIG. 2E illustrates the inheritable master feature of the invention;

P-0022[0022]FIG. 3A is a simplified block diagram of a redundant link management switch of the invention;

P-0023[0023]FIG. 3B is a block diagram of a control logic incorporated in a stacking module;

P-0024[0024]FIGS. 4A and 4B show a flowchart for identification of a failed link in accordance with the invention; and

P-0025[0025]FIGS. 5A and 5B show a flowchart for backup management in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

P-0026[0026] As illustrated in FIG. 2A, switches <b>210</b><i>a˜d </i>are stacked together to form a switch stack <b>200</b>. Each switch—to wit, <b>210</b><i>a, </i><b>210</b><i>b, </i><b>210</b><i>c </i>and <b>210</b><i>d</i>—is equipped with a stacking module, <b>212</b><i>a, </i><b>212</b><i>b, </i><b>212</b><i>c </i>and <b>212</b><i>d, </i>respectively. Each stacking module includes an uplink port and a downlink port. On the switch <b>210</b><i>b </i>of the stack <b>200</b> for example, uplink port <b>214</b><i>b </i>connects a next-higher switch, i.e. the switch <b>210</b><i>a, </i>and downlink port <b>216</b><i>b </i>connects a next-lower switch, i.e. the switch <b>210</b><i>c. </i>According to the invention, every two switches are connected to form a closed-loop link topology. That is, a link <b>220</b><i>a </i>is connected between a downlink port <b>216</b><i>a </i>of the stacking module <b>212</b><i>a </i>and an uplink port <b>214</b><i>b </i>of the stacking module <b>212</b><i>b. </i>A link <b>220</b><i>b </i>is connected between a downlink port <b>216</b><i>b </i>of the stacking module <b>212</b><i>b </i>and an uplink port <b>214</b><i>c </i>of the stacking module <b>212</b><i>c. </i>As well, a link <b>220</b><i>c </i>is connected between a downlink port <b>216</b><i>c </i>of the stacking module <b>212</b><i>c </i>and an uplink port <b>214</b><i>d </i>of the stacking module <b>212</b><i>d. </i>Specifically, there is a link <b>220</b><i>d </i>connected between a downlink port <b>216</b><i>d </i>of the stacking module <b>212</b><i>d </i>and an uplink port <b>214</b><i>a </i>of the stacking module <b>212</b><i>a. </i>The switches <b>210</b><i>a˜d </i>are connected together in the above-described manner to form the closed-loop link topology instead of a simple chain.

P-0027[0027] At least one switch in the switch stack <b>200</b> can be equipped with an agent module, e.g. management module <b>222</b>. In one embodiment, the management module <b>222</b> is installed in the switch <b>210</b><i>b. </i>The management module <b>222</b> allows administrators to configure or monitor the switch stack using the network management applications. In addition, the management module <b>222</b> performs a redundant link management function. When the management module <b>222</b> is installed, the switch <b>210</b><i>b </i>becomes a redundant link management switch in the switch stack <b>200</b>. It should be understood to those skilled in the art that additional switches equipped with the management modules to provide fault tolerance are contemplated by the principles of the invention. As shown in FIG. 2D, for instance, a second management module <b>222</b>′ is installed in the switch <b>210</b><i>c </i>to serve as a backup.

P-0028[0028] Returning again to FIG. 2A, every unit IDs <b>218</b><i>a˜d </i>in the respective switches continues changing at power-on if the switches <b>210</b><i>a˜d </i>are connected with the closed-loop link topology in accordance with the invention. During power-on initialization, the management module <b>222</b> informs the stacking module <b>212</b><i>b </i>to block the signals of downlink port <b>216</b><i>b </i>so that the link <b>220</b><i>b </i>(marked ‘T’ in FIG. 2A) is terminated or isolated. As a result, the switches <b>210</b><i>a˜d </i>in the stack <b>200</b> transmit/receive control signals over a path including the links <b>220</b><i>a, </i><b>220</b><i>c, </i><b>220</b><i>d </i>like the simple chain, in which the link <b>220</b><i>b </i>is a redundant link for the stack <b>200</b>. After initialization, digit ‘1’ is assigned to the unit ID <b>218</b><i>b </i>of the switch <b>210</b><i>b, </i>digit ‘2’ is assigned to the unit ID <b>218</b><i>a </i>of the switch <b>210</b><i>a, </i>and digits ‘3’ and ‘4’ are respectively assigned to the unit IDs <b>218</b><i>d, </i><b>218</b><i>c </i>of the switch <b>210</b><i>d, </i><b>210</b><i>c. </i>

P-0029[0029] In case of a link or switch failure in the switch stack <b>200</b>, the redundant link <b>220</b><i>b </i>of the invention provides the ability to automatically recover from such failures. Referring to FIG. 2B, if the link <b>220</b><i>c </i>fails for some reason, the management module <b>222</b> informs the stacking module <b>212</b><i>b </i>to enable the downlink port <b>216</b><i>b </i>so as to reconnect the link <b>220</b><i>b </i>upon detecting the failure. Then, the switches <b>210</b><i>a˜d </i>are re-initialized and digits ‘3’, ‘2’, ‘1’, ‘4’ are respectively reassigned to the unit IDs <b>218</b><i>a˜d </i>of the switches <b>210</b><i>a˜d </i>as depicted. With the redundant link <b>220</b><i>b, </i>the switches <b>210</b><i>a˜d </i>can be re-stacked together to form a new switch stack <b>200</b>′ without manual operation. In another example, where the switch <b>210</b><i>a </i>is down as shown in FIG. 2C, the redundant link <b>220</b><i>b </i>is reactivated to recover the stack from the failure. As depicted, digits ‘3’, ‘2’, ‘1’ are respectively reassigned to the unit IDs <b>218</b><i>b˜d </i>now and a new switch stack <b>200</b>″ is formed by the remaining switches <b>210</b><i>b˜d </i>in the manner described above.

P-0030[0030] A key goal of the invention is to provide a redundant link management switch which realizes the closed-loop link topology. Referring to FIG. 3A, a redundant link management switch includes a stacking module <b>312</b>, a processor <b>302</b> and a management module <b>322</b>. The stacking module <b>312</b> has an uplink port and a downlink port. The uplink port is used to connect a next-higher switch in a switch stack, and the downlink port is used to connect a next-lower switch in the switch stack. Of course, the terms up, down, higher, lower, etc., are merely for explanation and the physical locations of switches in the stack can vary, especially as switches are added, removed, or replaced. According to the invention, the redundant link is defined as a link connected between the downlink port of the redundant link management switch and the next-lower switch. In the case of two or more management modules within a stack of switches, the redundant link management switch is meant to be the switch assuming the master role.

P-0031[0031] The processor <b>302</b> instructs the stacking module <b>312</b> via a line <b>306</b> to disable a downlink control bus within the downlink port <b>316</b> when receiving a disconnect command, and instructs the stacking module <b>312</b> via the line <b>306</b> to enable the downlink control bus when receiving a reconnect command. The processor <b>302</b> also provides a link status, via a line <b>334</b>, to the management module <b>322</b>. In one embodiment, the stacking module <b>312</b> has a control logic <b>318</b> coupled to the downlink port <b>316</b> as shown in FIG. 3B. Typically, the signals passed through the downlink port <b>316</b> include a downlink control bus <b>342</b> and a downlink data bus <b>344</b>. When the processor <b>302</b> receives the disconnect command, it instructs the control logic <b>318</b> via the line <b>306</b> to isolate the redundant link by disabling the downlink control bus <b>342</b> within the downlink port <b>316</b>. When the processor <b>302</b> receives the connect command, it instructs the control logic <b>318</b> via the line <b>306</b> to recover the redundant link by enabling the downlink control bus <b>342</b>.

P-0032[0032] The management module <b>322</b> performs a redundant link management function. In one embodiment, the stacking module <b>312</b> has a manual control device <b>328</b>, such as a button, to enable the redundant link management function when the management module <b>322</b>, via a line <b>338</b>, detects that the manual control device <b>328</b> is activated. The stacking module <b>312</b> preferably includes an LED (not shown) to indicate whether the redundant link management function is enabled or not. According to the invention, the management module <b>322</b> issues the disconnect command via a line <b>304</b> to the processor <b>302</b> if the link status indicates that the redundant link management switch and the stack of switches are stacked into the closed-loop link topology. In one embodiment, the processor <b>302</b> generates a unit ID of the switch to signal the link status. In this regard, the link status indicates that the switches within the stack are arranged in a closed-loop link topology when the unit ID continues changing during initialization. The processor <b>302</b> reports the link status to the management module <b>322</b> accordingly. In addition, the management module issues the reconnect command via the line <b>304</b> to the processor <b>302</b> to recover the redundant link if the management module <b>322</b> detects that the closed-loop link topology has changed whenever a failure occurs in one of the switches or links within the switch stack.

P-0033[0033]FIGS. 4A and 4B illustrate the primary steps for identification of a failed link in accordance with the invention. Of course, every two switches in the switch stack are first connected via links including the redundant link to form the closed-loop link topology (step S<b>401</b>). Taking the stack <b>200</b> of FIG. 2A as an example, the redundant link is the link <b>220</b><i>b. </i>During power-on initialization, the management module <b>322</b> detects the link status (step S<b>403</b>). The link status is than checked to see whether the stack is arranged in the closed-loop link topology (step S<b>405</b>). If so, the redundant link in the stack is deactivated (step S<b>407</b>). Further, when the manual control device <b>328</b> for enabling the redundant link function is activated and the unit ID keeps changing, the control logic <b>318</b> is instructed to disable the downlink control bus <b>342</b> in the redundant link. Otherwise, a regular process for a stack connected as the simple chain can be executed (step S<b>406</b>). After initialization, each of the switches in the stack is assigned a fixed unit ID. Each switch is polled through the links within the switch stack (step S<b>409</b>). Although control signals in the redundant link are blocked, the switches <b>210</b><i>b </i>and <b>210</b><i>c </i>of FIG. 2A may still communicate with each other through the link <b>220</b><i>b. </i>If any link including the redundant link has failed, the disconnected location will be identified by the following steps of the invention.

P-0034[0034] If one of the switches in the switch stack fails to respond to the polling (step S<b>411</b>), the redundant link in the switch stack is activated (step S<b>413</b>). The control logic <b>318</b> is instructed to enable the downlink control bus <b>342</b> in the redundant link, thereby recovering the redundant link in the switch stack. Thereafter, the switches are re-initialized (step S<b>415</b>), and thus the switches can be re-stacked together to form a new switch stack without manual operation, in which the redundant link is activated. When the new stack is formed, the switches therein are reassigned to respective unit IDs (step S<b>417</b>). Notably, if a switch in the new switch stack has a downlink port with no active control signal, this switch is assigned to the lowest unit ID in accordance with the invention. Furthermore, another switch in the new switch stack is assigned to the highest unit ID if that switch has an uplink port with no active control signal. Referring again to the stacking recovery example of FIG. 2B, the unit ID of switch <b>210</b><i>c </i>is the lowest—‘1’ and unit ID of switch <b>210</b><i>d </i>is the highest—‘4’. In one embodiment, the management module serving as the master agent may keep a history record of link topology. Hence the history record is examined to determine whether the new switch stack has changed from the original closed-loop link topology to another link topology, namely the simple chain, after re-initialization (step S<b>419</b>). If the original closed-loop link topology has changed, the link connected between a switch with the lowest unit ID and another switch with the highest unit ID as a disconnected link (step S<b>421</b>). Taking FIG. 2B as an example, the link <b>220</b><i>c </i>is accordingly identified as the disconnected or failed link. The new switch stack can preferably send a trap to notify the network administrator of the actual location of the failed link.

P-0035[0035] To establish backup management and fault tolerance, two or more management modules must be installed in separate stackable switches. Once the manual control device <b>328</b> on a stacking module is activated in such a circumstance, the management module in the same switch as the stacking module has the highest priority to become a master agent for a stack of switches. The invention will be more clearly described by a flowchart in FIGS. 5A through 5B taken in conjunction with examples of FIGS. 2D and 2E. Referring to FIG. 2D, a stack <b>200</b> includes a switch <b>210</b><i>b </i>equipped with a management module <b>222</b> and a switch <b>210</b><i>c </i>equipped with a management module <b>222</b>′. From the beginning of FIG. 5A, a manual control device <b>328</b> on a stacking module <b>212</b><i>b </i>of the switch <b>210</b><i>b </i>is activated for example (step S<b>501</b>). Therefore, a link <b>220</b><i>b </i>attached to a downlink port <b>216</b><i>b </i>of the switch <b>210</b><i>b </i>is treated as a redundant link according to the above discussion. Then, the link <b>220</b><i>b </i>is deactivated by disabling a downlink control bus within the downlink port <b>216</b><i>b </i>(step S<b>503</b>). After that, unit IDs are assigned to respective switches in the stack <b>200</b> so the switch <b>210</b><i>b </i>has a particular unit ID, i.e., the lowest ID—‘1’ (step S<b>505</b>). According to arbitration between the management modules <b>222</b> and <b>222</b>′, the management module <b>222</b> in the switch <b>210</b><i>b </i>with the lowest unit ID is determined to be a master agent for the switch stack <b>200</b> and the management module <b>222</b>′ is determined to serve as a backup agent that takes over if the master agent fails (step S<b>507</b>). Next, the management module <b>222</b> synchronizes data with the management module <b>222</b>′ (step S<b>509</b>). If a link <b>220</b><i>d </i>fails as shown in FIG. 2E and causes disruption of the closed-loop link topology, the redundant link namely the link <b>220</b><i>b </i>is activated responsively (step S<b>511</b>). The switches <b>210</b><i>a˜d </i>are re-initialized to form a new switch stack <b>200</b>′″ in which the link <b>220</b><i>b </i>is activated now (step S<b>513</b>).

P-0036[0036] After re-initialization, the respective switches in the new switch stack are assigned new unit IDs and the lowest unit ID is specified to one of the switches whose downlink port has no active control signal (step S<b>515</b>). Referring to FIG. 2E, the unit ID of switch <b>210</b><i>d </i>is ‘1’ due to the failed link <b>220</b><i>d </i>and the unit IDs of the switches <b>210</b><i>a˜c </i>are ‘4’, ‘3’ and ‘2’, respectively. In this case, the unit ID of switch <b>210</b><i>c </i>is lower than the unit ID of the switch <b>210</b><i>b. </i>The management module <b>222</b>′ in the switch <b>210</b><i>c </i>enters a temporary master state to detect whether the management module <b>222</b> in the switch <b>210</b><i>b </i>with a higher unit ID is still active (step S<b>517</b>). If the management module <b>222</b> is inactive or failed, the management module <b>222</b>′ takes over the master role indeed to act as the master agent for the new switch stack <b>200</b>′″ (step S<b>518</b>). If the management module <b>222</b> is active and the manual control device of the switch <b>210</b><i>b </i>has been activated, the management module <b>222</b>′ exits the temporary master state and remains in the previous backup role. Consequently, the management module <b>222</b> in the switch <b>210</b><i>b </i>is determined to assume the master role for the new switch stack <b>200</b>′″ (step S<b>519</b>). Thereafter, the master agent re-synchronizes data with the backup agent (step S<b>521</b>). In this way, a management module in one switch takes precedence over any other management modules to become the master agent once the manual control device of that same switch is activated. Thus, that management module is enabled to inherit the master role from the previous and needs not change out of its role if possible. This prevents a switch stack from an unnecessary role change after automatic recovery of the redundant link.

P-0037[0037] Accordingly, the present invention discloses a scheme to automatically recover a switch stack in case of switch or link failure. The invention also proposes a way to detect a failed link within a stack of switches forming a closed-loop link topology. Moreover, a mechanism featuring the inheritable master role is provided to ease backup management in a stack of switches arranged in a closed-loop link topology.

P-0038[0038] While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.