User's Manual

Table Of Contents
365
Users Manual of CS-6306R
Chapter 39. Loopback Detection Configuration
Setting Loopback Detection 39.1
39.1.1 Introduction of Loopback Detection
The loopback in a network may trigger the repeated transmission of broadcast, multicast or unicast packets,
wasting network resources and even leaving network breakdown. To avoid the above-mentioned troubles, it is
necessary to provide a detection mechanism to promptly notify users of detecting network connection and
configuration at the occurrence of loopback and to take troubled ports under control. Loopback detection can
check whether loopback happens on a port of a to-be-tested device by transmitting a detection packet from
this port and checking whether this packet can be received still on this port. When the device finds that
loopback exists on its port, it can transmit alarm promptly to the network management system for
administrators to detect network problems in time; thus, long time of network disconnection can be prevented.
Moreover, loopback detection is capable of having ports under control. You can opt for port block, port
MAC-learning forbidding or error-disable according to actual requirements to make corresponding ports under
control and lessen the loopback's network influence to the minimum level.
The managed switches support loopback detection in the following aspects:
Supporting to set loopback detection on the port
Supporting to set the destination MAC address for loopback detection packets
Supporting to conduct loopback detection to at most 10 specified ports
Supporting to set the transmission interval of loopback detection packets and the recovery time of
controlled port
Supporting to control port, including port block, port MAC-learn forbidding, and error-disable
Supporting to set whether loopback exists on a port by default
39.1.1.1 Format of Loopback Detection Packet
Field
Length/Byte
Value
DMAC 6
0x0180C2B0000A (default value,
configurable )
SMAC 6
MAC address of the switch
TPID 2
0x8100, VLAN tag type
TCI 2
Specific value of the VLAN tag, priority,
VLAN ID
TYPE 2
Protocol type, which ranges from 0 to 9001
CODE 2
Protocol sub-type, which represents
loopback detection and is 0x0001
VERSION 2
0x0000 (currently reserved)
Length 2
0x0008, length of the header of loopback
detection packet
RESERVE 2
Reserved field