Edge-Core ES4624-SFP Basic Management Manual page 221

In the network topology, port g1/1 and port g1/2 of SWITCH A as well as port g1/3
and port g1/4 of SWITCH B are all fiber ports. And the connection is cross connection.
The physical layer is connected and works normally, but the data link layer is abnormal.
ULDP can discover and disable this kind of error state of link. The final result is that port
g1/1, g1/2 of SWITCH A and port g1/3, g1/4 of SWITCH B are all shut down by ULDP.
Only when the connection is correct, can the ports work normally (won't be shut down).
Switch A configuration sequence:
SwitchA(config)#uldp enable
SwitchA(config)#interface ethernet 1/1
SwitchA(Config-If-Ethernet1/1)#uldp enable
SwitchA(Config-If-Ethernet1/1)#exit
SwitchA(config)#interface ethernet 1/2
SwitchA (Config-If-Ethernet1/2)#uldp enable
Switch B configuration sequence:
SwitchB(config)#uldp enable
SwitchB(config)#interface ethernet 1/3
SwitchB(Config-If-Ethernet1/3)#uldp enable
SwitchB(Config-If-Ethernet1/3)#exit
SwitchB(config)#interface ethernet 1/4
SwitchB(Config-If-Ethernet1/4)#uldp enable
As a result, port g1/1, g1/2 of SWITCH A are all shut down by ULDP, and there is
notification information on the CRT terminal of PC1.
Fig 6-3 Fiber Cross Connection
Fig 6-4 One End of Each Fiber Not Connected
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