Could you reply with the configuration for interface switchport 0/1? Also, which firmware is the NetVanta 3120 currently running?
! ADTRAN OS version 18.01.01.00.E
! Boot ROM version 17.01.01.00
! Platform: NetVanta 3120, part number 1700601G2
sh interface sw 0/1
swx 0/1 is UP, line protocol is UP
Hardware address is 00:A0:C8:72:A3:CD
output flow control is disabled, 0 pause frames sent
input flow control is disabled, 0 pause frames received
ARP type: ARPA; ARP timeout is 20 minutes
Last clearing of counters never
5 minute input rate 142896 bits/sec, 67 packets/sec
5 minute output rate 551296 bits/sec, 76 packets/sec
Queueing method: fifo
Output queue: 0/256/0 (size/max total/drops)
Interface Shaper: NOT ENABLED
1513111 packets input, 279146394 bytes
1478439 unicasts, 18154 broadcasts, 16518 multicasts input
0 symbol errors, 0 discards
0 input errors, 0 runts, 0 giants
0 alignment errors, 0 crc errors
2025960 packets output, 2048509982 bytes
2007113 unicasts, 8018 broadcasts, 10829 multicasts output
0 output errors, 0 deferred, 0 discards
0 single, 0 multiple, 0 late collisions
0 excessive collisions
sh run (for sw 0/1)
interface switchport 0/1
Name: swx 0/1
Administrative Mode: access
Negotiation of Trunking: access
Access Mode VLAN (configured): 1
Trunking Native Mode VLAN: 1
Trunking VLAN Enabled: 1-4094
Trunking VLAN GVRP Fixed: none
Port Expiration: disabled
Port Security: disabled
I didn't see any issues in the configuration or statistics you sent of the NetVanta 3100. If there is a true duplex mismatch, more than likely you will see collisions and/or input errors on either side of the link. I did not see any on the NetVanta 3100. Generally, the rule of thumb regarding speed and duplex settings is that if the device the NetVanta is plugged into is set to auto-negotiate, then the NetVanta should also be set to auto-negotiate. If the device the NetVanta is plugged into is hard-set to a certain speed and duplex setting, then the NetVanta should be set to the same speed and duplex setting as the device.
It would be helpful to see the output of "debug lldp verbose" on the NetVanta 3100. Simply, telnet to the NetVanta, get into enable mode, and issue the "debug lldp verbose" command. It would be a good idea to log the output as the data maybe displayed faster than you'll be able to review it. To disable the debug, simply type in "u a". This will help us in seeing what the Netgear is telling the NetVanta via LLDP regarding its own speed and duplex.
Another option that would possibly provide more information is to set up a port mirror between the 3100 and the Netgear and capture the LLDP traffic between the two.
If you are able to get any debug, I would be more than happy to take a look at it for you.
I marked the question as "assumed answered" because there were no more follow up questions.
Please, do not hesitate to add additional information to this post if necessary.
As an update, in R10.11.0 AOS, a switchport command was added that allows an AOS switch the ability to ignore these LLDP speed-duplex mismatch messages. If you add the command "no lldp receive 802.3-info mac-phy-config" to any applicable switchports, the switch will no longer log every LLDP update indicating a mismatch as an event in the event-history.