H3C Technologies H3C S3600 Series Switches - Manual (Page 812)

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Tracing a device in a cluster
In practice, you need to implement the following in a cluster sometimes:
z Know whether there is a loop in the cluster
z Locate which port on which switch initiates a network attack
z Determine the port and switch that a MAC address corresponds to
z Locate which switch in the cluster has a fault
z Check whether a link in the cluster and the devices on the link comply with the original plan
In these situations, you can use the tracemac command to trace a device in the cluster by specifying a
destination MAC address or IP address.
The procedures are as follows:
1) Determine whether the destination MAC address or destination IP address is used to trace a
device in the cluster
z If you use the tracemac command to trace the device by its MAC address, the switch will query its
MAC address table according to the MAC address and VLAN ID in the command to find out the port
connected with the downstream switch.
z If you use the tracemac command to trace the device by its IP address, the switch will query the
corresponding ARP entry of the IP address to find out the corresponding MAC address and VLAN
ID, and thus find out the port connected with the downstream switch.
2) After finding out the port connected with the downstream switch, the switch will send a multicast
packet with the VLAN ID and specified hops to the port. Upon receiving the packet, the
downstream switch compares its own MAC address with the destination MAC address carried in
the multicast packet:
z If the two MAC addresses are the same, the downstream switch sends a response to the switch
sending the tracemac command, indicating the success of the tracemac command.
z If the two MAC addresses are different, the downstream switch will query the port connected with
its downstream switch based on the MAC address and VLAN ID, and then forward the packet to its
downstream switch. If within the specified hops, a switch with the specified destination MAC
address is found, this switch sends a response to the switch sending the tracemac command,
indicating the success of the tracemac command. If no switch with the specified destination MAC
address (or IP address) is found, the multicast packet will not be forwarded to the downstream any
more.
z If the queried IP address has a corresponding ARP entry, but the MAC address entry
corresponding to the IP address does not exist, the trace of the device fails.
z To trace a specific device using the tracemac command, make sure that all the devices passed
support the tracemac function.
z To trace a specific device in a management VLAN using the tracemac command, make sure that
all the devices passed are within the same management VLAN as the device to be traced.