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CCNP Enterprise Core (350-401) Cisco Datalink Layer

Troubleshooting Etherchannel

With the port channel being a logic interface, problems can occur if the physical member interfaces are not configured similarly.

Generally each member state must all be in either in a layer 2 or layer 3 port type, then associated with the port channel. The rest of the configuration should be done from the logical port channel interface.

There is a risk if configuration is done on individual member interfaces, they will no longer match with the rest of the interfaces. Here are factors that must be the same across all members of the port channel:

FactorDescription
Port TypeAll ports must be ethier in a Layer 2 switch port mode or Layer 3 routed port mode.
Port ModeLayer 2 ports must be configured as all access ports or all trunk ports, no mixing.
Native VLANLayer 2 ports must be configured with the same native VLAN across all members.
Allowed VLANsLayer 2 ports must have the same VLANs permitted across all members
SpeedAll member interfaces must have the same speed
DuplexAll member interfaces must have the same duplex
MTUAll Layer 3 interfaces must have the same MTU configured
Load intervalThe load interval must be configured consistently across all member interfaces
Storm ControlStorm control will need to be the same across all member interfaces.

In addition to the configuration settings matching, there are other factors in troubleshooting the establishment of an Etherchannel:

  • The link is directly attached between two devices
  • All the member ports are in an active state
  • Both ends are statically set to on, or:
    • If using LACP, one side is configured as active
    • If using PaGP, one side is configured as desirable

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