Hi Nagi-loon,
Auto-negotiation is enabled by default on all interfaces but only for advertised speeds.
In order to Enable auto-negotiation over all supported speed values you need to configure the interface speed to auto.
e.g.
SN2100 [standalone: master] (config) # sh interfaces ethernet 1/1
Eth1/1:
Admin state : Enabled
Operational state : Down
Last change in operational status: 0:05:11 ago (2 oper change)
Boot delay time : 0 sec
Description : N/A
Mac address : b8:59:9f:5b:d4:98
MTU : 1500 bytes (Maximum packet size 1522 bytes)
Fec : auto
Operational Fec : N/A
Flow-control : receive off send off
Supported speeds : 1G 10G 25G 40G 50G 56G 100G
Advertised speeds : 100G
Actual speed : Unknown
Auto-negotiation : Enabled
Width reduction mode : Unknown
Switchport mode : access
MAC learning mode : Enabled
Forwarding mode : inherited cut-through
Telemetry sampling: Disabled TCs: N/A
Telemetry threshold: Disabled TCs: N/A
Telemetry threshold level: N/A
Last clearing of “show interface” counters: Never
60 seconds ingress rate : 0 bits/sec, 0 bytes/sec, 0 packets/sec
60 seconds egress rate : 0 bits/sec, 0 bytes/sec, 0 packets/sec
The switch will auto-negotiate on 100G only. But now when I configure the speed to auto, you can see below that switch will auto-negotiate on all supported speeds and link comes up at 40G
SN2100 [standalone: master] (config) # interface ethernet 1/1 speed auto force
SN2100 [standalone: master] (config) # sh interfaces ethernet 1/1
Eth1/1:
Admin state : Enabled
Operational state : Up
Last change in operational status: 0:00:16 ago (3 oper change)
Boot delay time : 0 sec
Description : N/A
Mac address : b8:59:9f:5b:d4:98
MTU : 1500 bytes (Maximum packet size 1522 bytes)
Fec : auto
Operational Fec : no-fec
Flow-control : receive off send off
Supported speeds : 1G 10G 25G 40G 50G 56G 100G
Advertised speeds : 1G 10G 25G 40G 50G 56G 100G
Actual speed : 40G (auto)
Auto-negotiation : Enabled
Width reduction mode : Unknown
Switchport mode : access
MAC learning mode : Enabled
Forwarding mode : inherited cut-through
Telemetry sampling: Disabled TCs: N/A
Telemetry threshold: Disabled TCs: N/A
Telemetry threshold level: N/A
If the interface speed is set to auto, you cannot add it in Mlag port channel or regular port channel as it gives following error.
SN2100 [standalone: master] (config) # interface ethernet 1/1 mlag-channel-group 1 mode active
% Interface Eth1/1 must be configured only to one speed. Several speed values or “auto” option are not supported in mlag-channel-group.
Thanks,
Mellanox Support.