This is not about the Peer-link. peer link is just a normal trunk port which VPC will use. This Limitation is because of the different parameters on the both linecards module. YOU CAN NOT BIND TWO INTERFACES IN A LOGICAL BUNDEL IF THEY ARE OF DIFFERENT PERAMETER. https://www.cisco.com/c/en/us/td/docs/switches/datacenter/nexus5000/sw/configuration/guide/cli/CLIConfigurationGuide/EtherChannel.html
When you add an interface to a channel group, the Cisco NX-OS checks certain interface attributes to ensure that the interface is compatible with the channel group. The Cisco NX-OS also checks a number of operational attributes for an interface before allowing that interface to participate in the port-channel aggregation.
The compatibility check includes the following operational attributes:
Trunk native VLAN
Allowed VLAN list
802.3x flow control setting
This attribute is strictly not applicable as the Cisco Nexus 5000 Series switch only supports system level MTU.
Broadcast/Unicast/Multicast Storm Control setting
Use the show port-channel compatibility-parameters command to see the full list of compatibility checks that the Cisco NX-OS uses.
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