It is all spanning-tree related. D-down stands for diagnostically down, which occurs if more than 15 bpdus per second are received for 3 seconds. The switch shuts the port down. USL worker task is traffic related so a big spanning tree change would cause that to be really high. 
Hello everyone, we had a strange behaviour on one of our PowerConnect 8024F switches. The uplink port of the device (connected to a 10Gig port on a Cisco Catalyst 6513) went down. The output of 'show interfaces status' looked like that: Port       Description                Duplex  Speed    Neg   Link   Flow Control                                                             State  Status---------  -------------------------  ------  -------  ----  ------ ------------Te1/0/1    cat6500-rz-1 (te11/2)      Full    10000    Off   D-Down InactiveTe1/0/2    pc8024-ub-1 (te1/0/1)      Full    10000    Off   Up     ActiveTe1/0/3    pc8024-uv-1 (te1/0/1)      Full    10000    Off   Up     ActiveTe1/0/4    pc5500-naf02n-1 (te1/0/1)  Full    10000    Off   Up     ActiveTe1/0/5    pc5500-naf04n-1 (te1/0/1)  Full    10000    Off   Up     ActiveTe1/0/6    pc5500-naf03-1 (te1/0/2)   Full    10000    Off   Up     ActiveTe1/0/7    pc8024-mensa-1 (te1/0/1)   Full    10000    Off   Up     ActiveTe1/0/8    defekt                     N/A     Unknown  Auto  Down   InactiveTe1/0/9    pc5500-naf03-2 (te1/0/1)   Full    10000    Off   Up     ActiveTe1/0/10   pc5500-naf03-3 (te1/0/1)   Full    10000    Off   Up     Active... ...and so on. Firmware is 5.1.2.3. We rebooted the device and it went back to normal behaviour. Now, can anyone explain to me what the state "D-Down" means? I did not find anything in the documentation nor did using google have any success. The port configuration looks like the following: description "cat6500-rz-1 (te11/2)"mtu 9216switchport mode generalswitchport general allowed vlan add 4-5,14,22-27,29-33,36,39-41,43 taggedswitchport general allowed vlan add 47,51-52,54-56,58-60,63-64,66,75,78-79 taggedswitchport general allowed vlan add 81,86-90,93-99,107,120,122 taggedswitchport general allowed vlan add 124,132-135,137,140,142-143,147-152,154 taggedswitchport general allowed vlan add 156-157,160,165-166,171,173-175 taggedswitchport general allowed vlan add 177-178,180-181,183,189,192,195-196 taggedswitchport general allowed vlan add 199,201,203-205,207-208,210-212 taggedswitchport general allowed vlan add 219-222,224-225,227-233,235-244,246 taggedswitchport general allowed vlan add 248-249,253,256,258-260,262-267 taggedswitchport general allowed vlan add 269-272,274-276,278-279,282,284,286-288 taggedswitchport general allowed vlan add 292,295-298,323,344,347,349 taggedswitchport general allowed vlan add 354,362,366,370,372,378-380,382-383,385-386 taggedswitchport general allowed vlan add 391,399,405,431,443,447 taggedswitchport general allowed vlan add 475-476,485,488,511,522,584,700-703,710-714 taggedswitchport general allowed vlan add 725,734,838,854-855,909 taggedswitchport general allowed vlan add 950,961-962,981,999,1234,1236,2205,2218-2220 taggedswitchport general allowed vlan add 2222,2233,2414,2417 taggedswitchport general allowed vlan add 2506-2507,2519,2521,2621,2699 taggedmac access-group PVST-Filter out 1lldp transmit-tlv sys-name sys-caplldp transmit-mgmt The used mac access-group PVST-Filter is: mac access-list extended PVST-Filterdeny any 0100.0CCC.CCCD 0000.0000.0000permit any anyexit Thank you for reading and any suggestions! Robin
Uplink port on PowerConnect 8024F went to state D-Down