# Patent

## Title
Packet tracing through control and data plane operations using SNMP trap commands

## Abstract

Improved debugging capabilities for network packet path tracing. Embodiments trace both the control and data planes. During control plane operations each switch appends its identity to the payload, providing a full trace of the control plan path. SNMP Trap commands containing the forward path payload are provided back at each hop. The data plane is monitored by setting traps along the control plane path, with SNMP Trap commands at each hop being provided that indicate a given switch has been used.

## Background
RELATED APPLICATIONS
This application is a non-provisional application of Ser. No. 61/612,123, titled “B1-L2-Traceroute,” filed Mar. 16, 2012, of Ser. No. 61/650,380, entitled “Debugging Framework,” filed May 22, 2012, and of Ser. No. 61/673,218, titled “Tracepath's SNMP Trap and Network Management Software Processing Functionality,” filed Jul. 18, 2012, all three of which are incorporated by reference.
This application is related to application Ser. No. 13/786,604, entitled “Packet Tracing through Control and Data Plane Operations,” filed concurrently herewith, which is hereby incorporated by reference.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to networks, and more particularly to tracing paths of packets through a network.
2. Description of the Related Art
The industry is moving towards large layer-2 networks, using virtualized topologies such as fabrics, multi-chassis trunking (MCT) and virtual link aggregation groups (vLAG) to hide complexity. To debug these networks, the customer needs to uncover the complexity and trace the packet. However, this debugging is cumbersome and impractical today. This causes the customer to escalate the problems to the vendors. Studies have shown that very high percentages of these escalations involve packet loss and in each case the great majority of the time is spent identifying the culprit network node. Even for the vendors there is a lack of industry tools to easily debug layer-2 networks along the forwarding path as often multiple tools are needed to trace a single end-end layer-2 path. Indeed, there is no mechanism to locate layer-2 loops. The debugging is made more complicated because many problems have the same symptoms. Further, as the problems are present on production networks, no configuration changes can be done, there is live production background traffic and there is limited time to do the debugging.
Table 1 is a table of various debugging tools, their functionality and how specific situations are handled.











TABLE 1









Debugging






BUM






(Broadcast,





Blackhole
Unicast,


Tools
Functionality
L2 Loops
scenarios
Multicast) tree







Ethernet OAM
Link-trace to
Limited
Cannot trace
Limited


(Operations,
trace L2 path.

forwarding


Administration,
Mainly used

path hashed


and
between SP's.

based upon


Maintenance)


packet headers


(802.1ag/CFM


(Connectivity Fault


Management))


Brocade L2
Limited
VDX: N/A
VDX: Edge-
VDX: No


Traceroute
support for
MLX: Limited
port forwarding
support



tracing L2

not validated
MLX: Limited



packet path,

MLX: Does not



specific to a

validate



product line

forwarding





path


Cisco
CDP (Cisco
Limited
Does not verify
Does not cover


Traceroute mac
Discovery

forwarding
flooding



Protocol)

path
scenario



based, does not



apply to virtual



networks


ACL, SPAN &
Common tools,
Operator
Operator
Impractical in a


interface
but
should know
should know
failure scenario


statistics
cumbersome to
the
the



trace packet
problematic
problematic



path
link to capture
link to capture




data
data


Edge Loop
Detect loops
Detects, but
May detect
Flooding loops


Detection
based upon its
does not locate
loops, but does
detect, but not



returned

not locate
locate



heartbeat





Therefore it would be desirable to be able to more easily and completely debug packet flows in a network.






SUMMARY OF THE INVENTION
In an embodiment according to the present invention, a tracepath packet, a new diagnostic packet, is formed in a source device such as a switch. The forward tracepath packet is addressed with the MAC addresses, IP addresses, and UDP or TCP ports of the desired source and destination. By using the exact addresses and ports of the packets that are having problems, the complete path can be traced, as load balancing algorithms will operate in the same manner. Because this is a special purpose packet, when it is received at each switch or router it is provided to the switch or router control processor for handling. For this discussion the term switch will generally be used but it is understood that routers, bridges, gateways and the like are encompassed by the term switch when such other device operates in a manner equivalent to that described herein for packet forwarding.
Because the tracepath packet is provided to the control processor, it traverses the network along the control plane, as opposed to the data plane where normal packet traffic flows.
Each switch performs four functions for forward tracepath packets. First, the switch places its identity in the payload of the packet, so that the forward packet will ultimately include the entire path traveled in the payload, and sends the forward tracepath packet to the next hop, with the process repeated at the next switch. In doing this payload appending operation, the switch also scans the payload looking for its own identity. If found, this indicates a loop exists and forward tracepath packet operations are terminated.
Second, the switch develops a response tracepath packet which includes the identity of the switch where the response packet is being sent from as well as the payload of the forward tracepath packet. This response tracepath packet is sent out the port where the forward tracepath packet was received, so that the response tracepath packet will go to the source of the forward tracepath packet. If a loop was detected, this error information is also placed in the payload. When a response tracepath packet is received at a switch, the switch parses the payload looking for the switch's own information placed in the forward tracepath packet to determine which port received the forward tracepath packet, which information is preferably included in the appended information in addition to the switch identity, so that the return response tracepath packet can be sent out that port. If the switch's identity is not present in the payload, the response tracepath packet is a data plane response tracepath packet and a table developed during the forward tracepath packet operations is consulted to determine the egress port. This process is repeated at each switch or until the original source is reached by the response tracepath packet. This use of the same port results in the response tracepath packet traveling the same route as the forward tracepath packet, which insures that it will reach the original source, thus avoiding potential forwarding errors. By using the payload from the forward tracepath packet at each hop, the original source will receive response tracepath packets from each hop until an error occurs, if any, with the path up to the point of loss provided in the last response tracepath packet received.
Third, the switch sets a trap or filter to detect a regular data path packet having the same addressing. Fourth, the relevant information from the forward tracepath packet is stored in the table to allow response tracepath packet routing for data plane response tracepath packets to be identical to the forward tracepath packet route.
When the forward tracepath packet has traversed the path and no more response tracepath packets are received by the original source for a pre-determined period of time or a response tracepath packet including a “last-switch” indication is received, the original source develops a normal packet having the same addressing, except that a flag or marker is set to indicate the data plane packet of the debug operation. As this is a normal packet, it will be forwarded along the data plane rather than the control plane as was done for the forward tracepath packet. The normal packet is then transmitted into the network from the same port as the forward tracepath packet. The normal packet then follows the data plane path to the destination. As, during the control plane operations, each switch along the control plane path will have set the trap or filter, when the normal packet is received at the switch, the trap is triggered. The normal packet continues along the data plane path. The trap causes the switch to remove the trap to prevent denial of service problems when normal operations are resumed and to develop a new response tracepath packet which includes the identity of the switch developing the response tracepath packet in the payload. Thus data plane response tracepath packet is transmitted from the port identified in the table as the port receiving the forward tracepath packet. As this happens at each switch that both the forward tracepath packet and the normal packet traversed, the original source receives a response tracepath packet at each hop of the normal packet, so that the last data plane response tracepath packet received contains the last switch in the path until an error condition occurred, if any. Should the control plane path and the data plane path diverge, then the point of divergence will be detected as the next hop in the forward direction after the last switch identified in the last data plane response packet.
When broadcast or multicast packets need to be analyzed, the above operations could result in a flood of response tracepath packets to the original source. To simplify operation under those conditions, only selected switches in the network will have the capability enabled, as opposed to the prior example where it was assumed that the capability was enabled in all switches. This reduces the number of response tracepath packets to a more manageable number. To get the entire flooding tree, different switches can be enabled and the same packet addressing used until all switches have been used. The results can then be merged to reveal the overall paths.
The response tracepath packet contents, either by way of forwarding the entire packet or just the payload, are provided from the originating switch to a management station running management software, where the results are displayed.
As can be seen, the above operations verify both the control and data planes, rather than just the control plane in the prior art. Blackholes are readily detected based on determining and evaluating the last response tracepath packet in either plane. Layer 2 loops are readily detected. BUM (broadcast, unicast, multicast) packets can be used to allow full BUM tree analysis. The operations can be done without reconfiguring the network or stopping normal production operations, other than the operation being debugged. This allows debugging to be done during normal hours and as desired, not on a scheduled basis. In addition, the nature of the response tracepath packets allows the customer, rather than the vendor, to perform the majority of the debugging. The operations also work through the newer topologies such as fabrics, vLAGs and MCTs.
An alternate embodiment uses SNMP Trap commands instead of the response tracepath packets. The SNMP Trap commands use the normal UDP packets to the SNMP Manager (NMS). The SNMP Traps for the tracepath operations contain the same information as the response tracepath packets, the SNMP packets just are directed to the NMS instead of the originating switch. The use of SNMP Traps allows easier integration into existing NMS environments and the like, which often provide the most complete management of heterogeneous networks.
A further alternative allows the use of both response tracepath packets and SNMP Traps, allowing more flexibility for the system administrator.
While it is desirable that all switches include the capability, if there are intervening switches that do not implement the capabilities, the operations will continue at the next compliant switch, with a hop count value being used to make sure that the tracepath packets do not have an infinite life in a problematic network. The debugging software has the capability to receive the desired address information, the ability to develop the forward tracepath packets and the flagged normal packet with that addressing information at the desired injection point and the ability to receive and display the response tracepath packet payload information.



BRIEF DESCRIPTION OF THE DRAWINGS
The present invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates a network with selected problems in various locations.
FIG. 2 illustrates control plane tracepath packet tracing according to a first embodiment of the present invention.
FIG. 2A is a flowchart of forward tracepath packet operation in the control plane according to the first embodiment of the present invention.
FIG. 2B is a flowchart of response tracepath packet operation in the control plane according to the first embodiment of the present invention.
FIG. 3 illustrates data plane normal packet tracing and response tracepath packet according to the first embodiment of the present invention.
FIG. 3A is a flowchart of operation in the data plane according to the first embodiment of the present invention.
FIG. 4 illustrates flooding tree tracing according to the present invention.
FIGS. 5A-5C illustrate IP multicast tracing according to the first embodiment of the present invention.
FIG. 6 illustrates layer 2 loop location according to the first embodiment of the present invention.
FIG. 7 illustrates an exemplary switch according to the present invention.
FIG. 8 illustrates control plane tracepath packet tracing and SNMP Trap commands according to a second embodiment of the present invention.
FIG. 8A is a flowchart of tracepath packet and SNMP Trap command operation in the control plane according to the second embodiment of the present invention.
FIG. 9 illustrates data plane normal packet tracing and SNMP Trap commands according to the second embodiment of the present invention.
FIG. 9A is a flowchart of operation in the data plane according to the second embodiment of the present invention.
FIGS. 10A-10C illustrate IP multicast tracing according to the second embodiment of the present invention.
FIG. 11 illustrates layer 2 loop location according to the second embodiment of the present invention.
FIG. 12 is a block diagram of an exemplary network management system according to the present invention.



DETAILED DESCRIPTION
Referring now to FIG. 1, an exemplary network 100 is shown. An external workstation 102 is connected to an IP cloud 104, such as the Internet, which in turn is connected to routers 106A, 106B. The routers could be MLX routers from Brocade Communications Systems, Inc. (Brocade). A Layer 2 firewall 108 performs VLAN translations and other firewall functions and is connected to the routers 106A, 106B. The routers 106A, 106B are connected to a Layer 2 fabric no, such as the VCS fabric from Brocade. The Layer 2 fabric no is formed by a series of switches 112A-J, example switches being VDX switches from Brocade. A series of stackable edge switches 114A-G are illustrated as being connected to the Layer 2 fabric no. Example stackable edge switches are FCX switches from Brocade. Another switch 116 is connected to switch 114A in the example to provide a switch connected to a local workstation 118.
In the illustrated embodiment external workstation 102 pings the local workstation 118 but the ping request times out, indicating an error somewhere in the network 100. Five errors are shown as being present in the network 100. The first error 120 is that the System MAC has been permanently moved from router 106A to 106B due to a layer-2 loop. This would potentially cause black-holing of traffic. A second error 122 is that a number of the MACs in the switches 112A-G that form the Layer 2 fabric no are incorrectly programmed. A third error 124 is that one of the MACs on switch 112D is out of synchronization with the remainder of the switches 112. A fourth error 126 is that switch 114A has an ARP table error. The fifth error 128 is a layer 2 loop misconfiguration inside switch 116. The first four errors 120-126 could result in blackholes, causing the ping from external workstation 102 to be lost. The layer 2 loop error 128 will simply trap the ping until the ping times out. These are examples of the errors discussed in the Background that are very hard to diagnose and debug.
A management station 130 is connected to the network 100 to allow interaction with the various routers and switches.
In the preferred embodiment a user operating a management workstation 130 connected functionally to a router 106B would use a tracepath command of the following syntax. The tracepath command can be provided through a proprietary interface or API with a management program, a CLI (command line interface) or through a more standardized messaging interface such as one based on the OpenFlow standard. Depending upon the issue being debugged, the tracepath command can be sent to access, aggregation (fabric) or core layer switches or routers, with that switch or router controlling debugging operations and transmitting and receiving relevant packets. The below scenario gives example of entering the command on core switches or routers.
MLX# tracepath <l2 hdr> <l3 hdr> <l4 hdr> <vlan> <hop-count> <switch-names> <Priority> <in-port>
MLX# is the originating switch identifier, such as that of router 106B. tracepath is the command. <l2 hdr> is the MAC addresses of the source and destination, such as the MACs of external workstation 102 and local workstation 118. <l3 hdr> is the IP addresses of the source and destination. <l4 hdr> is the ports, such as TCP or UDP, of the source and destination. <vlan> is the relevant VLAN. <hop-count> is conventional. <switch-names> is a list of switches to be enabled for this operation. The default is all switches. <Priority> identifies the priority of the packet, to allow priority-based debugging as well. <in-port> is the specific input port of the originating switch, such as the port connected to the IP cloud 104 in the example of FIG. 1.
Operation according to the preferred embodiment starts at FIGS. 2, 2A and 2B. In step 220, the source router 202 receives the tracepath command from the management station 130. In step 222, the forward diagnostic tracepath packet is generated. A special ethertype is preferably used to denote the tracepath packet, though other markers could be placed in various portions of the headers. The destination addresses, layer 2, layer 3 and layer 4, are based on the impacted device, such as workstation 212. It is understood that not all three layer addresses need be provided in operation and that in an alternate embodiment masks could also be used for each address. The source addresses, again layer 2, layer 3 and layer 4, are the router 202 MAC address and the impacted source layer 3 and layer 4 values, as provided in the tracepath command, as the router would have replaced the MAC address of the actual source, such as an external workstation but layer 2 and 3 addresses would be unchanged. If the originating device is a switch instead of a router, the source MAC address would be different, such as that of the relevant router if the impacted device is beyond the router or the source MAC address if on the same layer 2 network segment. The tracepath packet type is provided in the payload, along with any desired details on the impacted packet, the chassis MAC address and/or switch name (indicated as M0 in the hop from switch 202 to switch 204) and optionally the egress or output port information. A flag can be set in the packet to indicate a forward direction packet if only a single ethertype is to be used for the forward and response packets. This packet is provided to the switch 204.
At step 224 a tracepath packet is received at the switch 204. The packet processor 706 (FIG. 7) of the switch port forwards the tracepath packet to the switch CPU 710 upon detection of the ethertype indicating the tracepath packet in step 226. In step 227 the CPU 710 determines if the tracepath packet is a forward packet or a response packet. If a forward packet, in step 228 the CPU 710 scans the payload looking for its own MAC address, indicating a loop condition.
In step 230, if the own MAC address is not found, then in step 232 a TRAP entry is programmed into the switch hardware 702, such as in the packet analysis module 732. The TRAP entry is looking for a normal packet with the same headers as the forward tracepath packet and preferably with a flag set. The TRAP entry is preferably set with an expiration value so that the TRAP entries get automatically removed if the data plane portion of the operations do not occur. In step 234, the VLAN information, ingress port and MAC address list from the payload are stored in a table to allow a return or response tracepath packet to be provided out the same port on the same VLAN. In step 236 the switch's chassis MAC address and/or switch name is appended to the payload to allow tracking of the hops. The ingress and egress port information can be added if desired. This appending is shown in FIG. 2 as the addition of a value in the payload, such as Mo in the first hop, Mo, Mi in the second hop and Mo, Mi, M2 in the third hop.
In step 240 a response tracepath packet is generated by the CPU 710. The response tracepath packet reverses the source and destination addresses of the forward tracepath packet and has the payload of the forward tracepath packet, including the information on the current switch. The payload is shown in
FIG. 2 as the numbers in the packet, such as Mi, Mo in the hop from switch 204 to switch 202. The response tracepath packet is sent out the ingress port where the forward tracepath packet was received. In an alternate embodiment, step 240 is performed before step 236 so that the response tracepath packet payload does not contain the information of the switch generating the response tracepath packet. For example in FIG. 2, the M1 would not be present in the packet from switch 204 to switch 202. In this embodiment the identity of the originating switch, such as switch 204, can be determined by analyzing the layer 2 source address of the response tracepath packet.
In the illustrated case, the forward tracepath packet traverses a non-Brocade portion 206 of the network. This is exemplary for any portion of the network that must be traversed and that does not comprehend the tracepath packet. The above operations from step 224 are performed by the next switch, such as switch 208, and then the next switch, such as switch 210. This repeated operation is illustrated in FIG. 2A as a determination of whether the last switch has been reached in step 242. If not, the operation proceeds to step 244, where the updated forward tracepath packet is forwarded out the proper egress port based on the hash operations that are in place, with the hash being performed by the CPU 710 in software as the packet will actually be directly placed in the egress port after the switch routing hardware. Operation then returns to step 224, effectively the operation of the next switch.
Returning to step 230, if the switch's own MAC address was found, in step 238 a response tracepath packet is generated as above in step 240 except a code indicating the loop error is also placed in the payload. Because of the error, the debugging operation stops after step 238. The set TRAP entries will expire based on their timer values, so no data plane operations are required.
If it was determined in step 227 that the tracepath packet was a response packet and not a forward packet, then in step 260 the CPU 710 reviews the packet payload and potentially the table of stored information, the VLAN information, the ingress port and the MAC address list as stored in step 234, to determine the egress port and VLAN for the response tracepath packet. If this is a control plane response tracepath packet, the payload contains the switch information of the prior hops. Thus, the switch information, which preferably includes the ingress and egress ports, of the present switch should be present. As a result, the stored ingress port can be used as the egress port for the response tracepath packet. If this is a data plane response tracepath packet, information of a single switch is present, not the present switch. Therefore, the switch CPU 710 consults the stored list to determine the proper egress port. The response tracepath packet is then transmitted out that port in step 262. Thus the response tracepath packet will traverse the forward path in the reverse direction, insuring that the response tracepath packet will reach the originating source. When the originating source detects the packet, the originating source captures the packet and provides at least the payload and addressing information to the management station 130. The originating source or switch does not further transmit the response tracepath packet into the network, except partially as a payload of a packet to the management station 130.
For the example network of FIG. 2, response tracepath packets will be provided by switch 204, switch 208 and switch 210. The originating switch or router will forward the payloads of these responses to the management station 130 for review by the user. In the illustrated case of proper routing and no errors, the return of the three response packets will show that the forward tracepath packet would have reached the destination. If instead the response tracepath packet from switch 210 was not received by the originating switch, this would indicate a routing failure between switch 208 and switch 210, as the last response tracepath packet would have been received from switch 208. Thus a blackhole or lost packet is easy to trace as the last switch that successfully received the packet before the error is provided. The user can then quickly check just that switch for routing error sources. Thus the location of the blackhole is very naturally provided, greatly simplifying debug efforts.
Because all of the routing decisions described above were made by the switch CPU 710, this forward tracepath packet thus traverses the control plane, thereby checking the control plane routing tables and the like. However, data plane checking must also be done as the data plane routing and the control plane routing may not be the same, which could result in routing errors and lost packets.
Referring to FIGS. 3 and 3A, data plane diagnostic operation after the control plane operation of FIGS. 2, 2A and 2B is shown. If the last switch was reached in step 242, operation proceeds to step 302. In certain embodiments this last switch determination is actually done in each switch, either by checking the hop count or based on LLDP (link layer discovery protocol) or similar information, so that the last switch can also add a last switch indication in the payload of its response tracepath packet of step 240. Understanding that the last switch decision is just for explanatory purposes in some embodiments, step 302 would actually commence a sufficient period after the last response tracepath packet was received for those embodiments. If a specific last switch indication was placed in a response tracepath packet in the embodiment, then step 302 occurs after receipt of that packet. In step 302 a normal packet is generated in the switch 202. The addressing is the same as the forward tracepath packet of step 222 to test the data plane. A data plane flag is set in the normal packet, preferably on one of the header fields. A normal or nominal payload is used as there is no actual data to be transmitted, just the path of the normal packet monitored. The normal packet is then issued from the switch 202, as indicated by the straight arrow, as opposed to curved arrows which represent control plane operations. The normal packet is received at switch 204 in step 304. As the addresses of the packet match those previously set for the TRAP entry and the data plane flag is set, the TRAP is generated in step 306. The normal packet is next transmitted from the switch using the normal hardware routing operations in step 308. This allows testing of the hardware routing operations, as opposed to the control plane routing done previously.
In step 310 a response tracepath packet is generated based on the TRAP. The address is the original source, with the switch's MAC address placed in the payload. Only the MAC address of the one switch is present in this response tracepath packet as there is no opportunity to edit the payload as done in the control plane tracing, as the intent of this phase is to have the normal packet proceed along the normal hardware route. The response tracepath packet is transmitted out the same port as the control plane diagnostic packet was received, as true with the response tracepath packets in the control plane phase. In step 312 the TRAP entry is removed so that only the one use of the normal packet triggers the debugging response packet generation. If not removed and if normal operations resumed before the TRAP timer value expired, the TRAP might happen for each packet in normal operations, which should be avoided. In step 314 a determination is made if this is the last switch. As in step 242, this step is provided to illustrate that the same operations occur in each switch, not that the decision step itself is actually present. If not the last switch, operation returns to step 304 so that the next switch in the network performs the same operations and sends the response tracepath packet to indicate the next hop has been reached.
The switch 202 receives a response tracepath packet for each hop the normal packet travels that is the same as the control plane operation. This allows the data plane response tracepath packets with their payloads to be forwarded to the management system 130, which can then trace the path of the normal packet hop by hop. When no further response tracepath packets are received, the normal packet has either reached its destination or has been lost after the last switch that provided a response tracepath packet. Assuming the lost packet, debug analysis can begin at the last switch that provided a response tracepath packet as the packet got lost exiting that switch.
Management software on the management workstation 130 then displays the debugging test results as desired, such as simple textual tables or as full topology displays with the paths and switches of the control plane and data plane highlighted or emphasized, such as one or two different colors or the like.
The above discussion assumes that all switches in the network have the features enabled, unless otherwise indicated. This is useful in cases as discussed above, where individual source or destination addresses are of concern. However, if the problems being debugged are occurring in multicast or broadcast packets, having all of the switches enabled could easily overwhelm the originating switch. This problem is addressed by use of the <switch-names> option in the tracepath command described above. Only the desired switches are listed in the command, the remaining switches being disabled. This limits the number of response tracepath packets being provided. If the fUll trees are to be analyzed, this can be done by multiple executions of the tracepath command and varying the enabled switches based on the expected tree. The response tracepath packets from the multiple executions can then be combined to show the full tree results.
An example is illustrated in FIGS. 4 and 5 A-C. As a precursor, the tracepath command is issued such that the destination MAC address is a multicast or broadcast address and/or the destination IP address is a broadcast or multicast address. Further, the desired switches are listed in the <switch-names> portion of the command. In FIG. 4, the network of FIG. 1 is illustrated without the errors, and like switches receive like numbers. The switches of interest for the first phase are circled, namely switches 112A, 112B, 112C, 112D and 114A, which are enabled by the tracepath command. The remainder of the switches have the tracepath feature disabled due to the operation of the tracepath command. The switches are enabled or disabled based on the presence of their names or identifying information being present in the packet payload, the names being added by the source based on the <switch-names> filed in the initial command. In the preferred embodiments the switches know to look for their name in this list based on a bit in the payload which indicates unicast mode, where each switch responds to the packet, or broadcast/multicast mode, where only the listed switches respond.
The operation is generally as described above for the specific unicast example, except the forward tracepath and normal packets are distributed to multiple switches in parallel and response tracepath packets are received from each. FIGS. 5A-5C illustrate three iterations of the control plane and data plane operations through three different sets of enabled switches, with the flow through the switches where tracepath functionality is not enabled not shown. FIG. 5A shows operation through switches 112A, 112D and 114A. FIG. 5B shows operation through switches 112A, 112C and 114A. FIG. 5C shows operation through switches 112B, 112E and 114D. It is understood that this can be done for all of the various switches if the full flooding pattern is desired or only for a lesser portion if the problem area of concern is more localized.
The management software on the management workstation 130 collects all of the responses and then either displays the results individually if desired or accumulates the results until all desired iterations have been completed, with the accumulated results then being displayed.
The flowchart of FIG. 2A at steps 228, 230 and 238 cover the case of a layer 2 loop. That case is illustrated in FIG. 6. The forward tracepath packet hops forward one switch at a time, from switch 600 to switch 602 to switch 604 to switch 606 to switch 608 to switch 610 and then back to switch 606. Switch 606 detects its MAC address in the payload of the forward tracepath packet and thus detects the layer 2 loop error. The response tracepath packet that is generated includes the switch path up to switch 606 the second time and then an entry indicating the loop detection by switch 606. Switch 606 does not forward the forward tracepath packet, as debugging operations terminate due to the loop error. The existing TRAPs in switches 602, 604, 606, 608 and 610 expire based on their expiration time values.
FIG. 7 illustrates an exemplary switch 700 according to the present invention. The switch hardware 702 includes a series of packet processors 706 which provide the switch ports 707. Each packet processor 706 includes a policy routing table 730 for routing packets and a packet analysis module 732, which analyzes packet headers and the like for desired information. The packet processors 706 are connected to a switch fabric 708 to allow packet switching. A switch CPU 710 is connected to the switch fabric 708 to allow packets to be forwarded from the packet processors 706 to the switch CPU 710 for further analysis and handling. A memory 711 is connected to the CPU 710 and holds program instructions executed by the CPU 710 to perform the various operations. These program instructions include an SNMP agent 712 to handle the SNMP operations. In the preferred embodiments the packet processors 706 detect the received tracepath packets and forward them through the switch fabric 708 to the CPU 710. The new response tracepath packets are provided directly to the proper packet processor 706 using a control plane operation (not illustrated) so that the desired egress port can be assured. Alternatively, if the switch 700 uses shims or other additional information with each packet internally to transfer the routing information, the switch CPU 710 can use the switch fabric 708. The packet processors 706 also contain the TRAP logic, which causes an interrupt or similar message to be provided to the switch CPU 710. This is an exemplary switch architecture and many variations and further details are well known to those skilled in the art. Given the above description one skilled in the art can modify those variations to provide similar functionality to that described herein. In some of the variations certain operations described as being done by the CPU 710 may be done in hardware, such as developing the response tracepath packets, if the hardware is sufficiently advanced to provide hardware modules to perform the operations.
In an alternate embodiment, instead of, or in addition to, response tracepath packets, SNMP Traps are used. The SNMP MIB in each switch is extended to include tracepath functions, such as receiving the Set commands and providing the Traps. The use of SNMP Traps allows integration into conventional SNMP Management environments, which often are more useful in more heterogenous environments than proprietary management programs provided by switch vendors. The proprietary management programs may provide more detailed control or data collection for the related switches, so they may be used as necessary for those capabilities, but normal activities may be more easily handled with a NMS. Problems may be highlighted on the NMS and then the proprietary system can be used for further details and operations if needed or if easier.
Referring to FIGS. 8 and 8A, these are generally FIG. 2 with SNMP Trap commands substituted for the response tracepath packets. A NMS 800 provides the tracepath command as discussed above to the switch 202 using an SNMP Set command. The switch 202 receives this command in step 820. As in the embodiment of FIG. 2, a tracepath packet, equivalent to the forward tracepath packet of the FIG. 2 embodiment, is generated and transmitted. The tracepath packet is received at switch 204, which performs steps 824, 826, 828, 830, 832, 834 and 836 in the same manner as steps 224, 226, 228, 230, 232, 234 and 236. The description of those steps is omitted here for brevity. After step 836, in step 840 the SNMP Trap command is generated by the switch, as opposed to the response tracepath packet of step 240. The SNMP Trap command contains the same information, namely the appended list of chassis MAC addresses, ingress and egress ports and the like. However, instead of using the ingress port, normal SNMP methods are used, such as the UDP packet to the NMS 800. The SNMP Trap commands are illustrated as dashed lines to the NMS 800 in FIG. 8. Steps 842 and 844 are performed the same as steps 242 and 244.
There is no equivalent to step 227 or steps 260 and 262 of FIG. 2B as those only relate to response tracepath packets and those have been removed in the SNMP Trap command embodiment.
If in step 830 the switch determined that its own MAC address was present, then in step 838 a SNMP Trap command is sent with the appended list of chassis MAC addresses and the loop error details. This is similar to step 238 except an SNMP Trap command is used instead of a response tracepath packet.
FIGS. 9 and 9A are the SNMP Trap versions of the data plane operations of FIGS. 3 and 3A. As shown in FIG. 9, SNMP Trap commands are sent from the switches 204, 208 and 210 to the NMS 800 as opposed to the response tracepath packets of FIG. 3. As a switch is not present to receive response tracepath packets, the last switch determination, whether based on explicit indication in an SNMP Trap command or based on a timer from the last received SNMP Trap command, is preferably done by a JAVA applet which is a plugin to the NMS software module. When the JAVA applet determines that it is proper to begin data plane operations, an SNMP Set command is sent to the switch. This Set command is received in step 900. Steps 902, 904, 906, 908 and 914 are the same as their counterparts in FIG. 3A. In step 910, an SNMP Trap command is used instead of the response tracepath packet.
FIGS. 10A, 10B and 10C are the alternate SNMP Trap embodiment applied to the multicast/broadcast operations of FIGS. 5A, 5B and 5C, where the response tracepath packets are replaced by SNMP Trap commands. FIG. 11 similarly is the alternate SNMP Trap command embodiment version of the layer 2 loop example of FIG. 6.
FIG. 12 is a block diagram of an exemplary NMS 800. A CPU 1202 performs normal processing functions and is connected to RAM 1204 for working storage. A system interconnect 1206 is connected to the CPU 1202 to allow various other devices to be coupled to the CPU 1202. For example, storage 1208 is connected to the interconnect 1206. The storage 1208 is used for program storage and includes an NMS module 1210 and a JAVA applet 1212 which is a plugin to the NMS module 1210 as discussed above. An output block 1216 is connected to the interconnect 1206 and receives a display 1218. An input block 1220 is also connected to the interconnect 1206 and has a mouse 1222 and a keyboard 1224 connected. A network interface card (NIC) 1214 is connected to the interconnect 1206 to allow the NMS 800 to be connected to the network to send and receive SNMP commands. This is understood as an exemplary block diagram and many other architectures and design are suitable to act as the NMS 800 and execute the NMS module 1210 and the JAVA applet 1212.
Embodiments according to the present invention provide improved debugging capabilities for network packet path tracing. Embodiments trace both the control and data planes. During control plane operations each switch appends its identity to the payload, providing a full trace of the control plan path. Responses are provided back at each hop, the responses being routing back by tracing back the forward direction control plane or by use of SNMP Trap commands. The data plane is monitored by setting traps along the control plane path, with responses at each hop that indicate a given switch has been used being returned along the control plane path. Broadcast and multicast traffic is monitored by selecting particular switches to perform the above operations. Layer 2 loops are detected by each switch monitoring the control plane packets for presence of that switch in the payload. A management station collects the responses and provides an output for user analysis. Thus embodiments according to the present invention simplify path debugging and cover instances not previously covered. Further, the debugging operations can occur during production operation as the various packets are simply interspersed with the production traffic.
The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this disclosure. The scope of the invention should therefore be determined not with reference to the above description, but instead with reference to the appended claims along with their full scope of equivalents.

## Claims

1. A method comprising:
receiving and detecting a tracepath packet at a device and providing said tracepath packet to a CPU of the device, said tracepath packet having addressing of packets being traced;
appending the device information to payload information of the tracepath packet and transmitting said tracepath packet with said appended payload from the device;
generating and transmitting, responsive to receiving and detecting said tracepath packet, a first SNMP Trap command by the device, said first SNMP Trap command including the payload of said tracepath packet;
enabling detection of a tagged normal packet by the device based on receipt of said tracepath packet;
receiving and detecting said tagged normal packet by the device after transmitting said first SNMP Trap command;
transmitting said tagged normal packet from the device;
notifying the CPU of the device of the detection of said tagged normal packet; and
generating and transmitting a second SNMP Trap command by the device in response to said notifying, said second SNMP Trap command including the device information as information in said second SNMP Trap command.

2. The method of claim 1, further comprising:
analyzing payload information of said tracepath packet for presence of the device information by the device;
omitting transmission of said tracepath packet and detection of a tagged normal packet if the device information is present; and
including an error indication in said first SNMP Trap command if the device information is present.

3. The method of claim 1, further comprising:
disabling detection of the tagged normal packet after receipt of the tagged normal packet.

4. A method comprising:
receiving a command from management device in an SNMP Set command to transmit a tracepath packet at an originating device, said command indicating source and destination addresses of said tracepath packet;
developing and transmitting said tracepath packet in response to said command by the originating device;
receiving and detecting said tracepath packet at a switching device and providing said tracepath packet to a CPU of the switching device, said tracepath packet having addressing of packets being traced;
appending the switching device information to payload information of the tracepath packet;
transmitting said tracepath packet with said appended payload from the switching device;
generating and transmitting, responsive to receiving and detecting said tracepath packet, a first SNMP Trap command by the switching device, said first SNMP Trap command including the payload of said tracepath packet as a portion of said first SNMP Trap command;
developing and transmitting a tagged normal packet after transmitting said tracepath packet, said tagged normal packet having the same addresses as said tracepath packet and including a tag;
enabling detection of said tagged normal packet by the switching device based on receipt of said tracepath packet;
receiving and detecting said tagged normal packet by the switching device;
transmitting said tagged normal packet from the switching device; notifying the CPU of the switching device of the detection of said tagged normal packet; and
generating and transmitting a second SNMP Trap command by the switching device in response to said notifying, said second SNMP Trap command including the switching device information as information in said second SNMP Trap command.

5. The method of claim 4, wherein said steps of receiving and detecting said tracepath packet at a switching device, appending the switching device information to payload information, transmitting said tracepath packet with said appended payload, generating and transmitting a first SNMP Trap command by the switching device, enabling detection of said tagged normal packet by the switching device, receiving and detecting said tagged normal packet by the switching device, transmitting said tagged normal packet from the switching device, notifying the CPU of the switching device of the detection and generating and transmitting a second SNMP Trap command by the switching device are repeated for each switching device capable of performing such steps in the path from the originating device to a later device.

6. The method of claim 5, wherein one of the addresses of said tracepath packet is a broadcast or multicast address,
wherein said command further indicates a list of switching devices to be enabled to perform such steps so that switching devices not enabled are considered to not be capable of performing such steps, and
wherein only indicated switching devices are enabled and remaining switching devices are not enabled.

7. The method of claim 4, further comprising:
analyzing payload information of said tracepath packet for presence of the switching device information by the switching device;
omitting transmission of said tracepath packet and detection of a tagged normal packet if the switching device information is present; and
including an error indication in said first SNMP Trap command if the switching device information is present.

8. The method of claim 4, further comprising:
disabling detection of the tagged normal packet after receipt of the tagged normal packet by the switching device.

9. A switch comprising:
a CPU;
memory coupled to and containing software instructions for said CPU;
a plurality of ports for receiving a tracepath packet, said tracepath packet having addressing of packets being traced, for transmitting a tracepath packet with an appended payload, for transmitting a first SNMP Trap command, for receiving a tagged normal packet, and for transmitting said tagged normal packet and a second SNMP Trap command including the switch information as payload information; and
at least one packet processor coupled to said CPU and to at least one of said plurality of ports to analyze packets received by said at least one of said plurality of ports, said at least one packet processor detecting said tracepath packet, providing said tracepath packet to said CPU, being enabled for detecting and detecting said tagged normal packet, and notifying said CPU of said detection of said tagged normal packet;
wherein said CPU operates to append switch information to payload information of said tracepath packet, to provide said tracepath packet with said appended payload to a port of said plurality of ports, to generate a first SNMP Trap command including the payload of said tracepath packet, to enable detection by said at least one packet processor of said tagged normal packet and to generate a second SNMP Trap command in response to said notifying, said second SNMP Trap command including the device information as information in said second SNMP Trap command.

10. The switch of claim 9, wherein said CPU further operates to analyze payload information of said tracepath packet for presence of the switch and to include an error indication in said first SNMP Trap command if the switch information is present, and
wherein said CPU further omits providing said tracepath packet to a port of said plurality of ports and enabling detection of said tagged normal packet if the switch information is present.

11. The switch of claim 9, wherein said CPU further operates to disable detection of the tagged normal packet by said at least one packet processor after receipt of the tagged normal packet.