Member ports must have same values for:
- Speed & duplex
- trunking/access mode, DTP mode
- same access VLAN
- same trunk type, allowed & native vlans
- same STP cost per VLAN
- no SPAN configured
Switch shuts down all physical ports when no interface port-channel [n] to avoid loop.
spanning-tree etherchannel guard misconfig for the same purposes (BPDUs received via both ports).
PAGP: 8 links max; 01:00 :0c:cc:cc:cc
LACP: 16 links max, 8 active max, 8 standby; 01:80:C2:00:00:02
channel-protocol: interface command. refuse any modes keywords other than configured under this command