CCNP SWITCH Etherchannel Course: Troubleshooting Tips

Previously in this free CCNP SWITCH Etherchannel course, we covered Etherchannel fundamentals,  PaGP and LACP operation, and when the XOR operation comes in.

To wrap things up, I want to share a list of Etherchannel rules and troubleshooting tips.  Knowing these will not only add points to your exam score, but will really come in handy in real-world networking.  Enjoy, and thanks for making my work part of your CCNP SWITCH success!

Chris Bryant’s CCNP SWITCH Study Guide

Cisco Press CCNP SWITCH Study Guide

Ports configured for dynamic VLAN assignment from a VMPS cannot become part of an Etherchannel, nor can it remain one if that change occurs after the port is already part of an Etherchannel.

The allowed range of VLANs on the ports in the EC must match that of the port-channel itself.  Here’s what happened after I changed the range of allowed VLANs on all ports in SW3’s EC without doing so on the port channel:

SW3(config-if-range)#switchport trunk allowed vlan 100,20

%EC-5-CANNOT_BUNDLE2: Fa0/22 is not compatible with Po5 and will be suspended (vlan mask is different)

%EC-5-CANNOT_BUNDLE2: Fa0/23 is not compatible with Po5 and will be suspended (vlan mask is different)

%EC-5-CANNOT_BUNDLE2: Fa0/24 is not compatible with Po5 and will be suspended (vlan mask is different)

%EC-5-CANNOT_BUNDLE2: Fa0/23 is not compatible with Po5 and will be suspended (vlan mask is different)

Not good!  However, once I went to SW2 and ran the same command, the EC came back up.

SW2(config)#int range fast 0/21 - 24

SW2(config-if-range)#switchport trunk allowed vlan 100,20


SW2#show etherchannel summary

(Flags removed)

Number of channel-groups in use: 1

Number of aggregators:           1


Group  Port-channel  Protocol    Ports

------+-------------+-----------+-------------------------------------

1      Po1(SU)         LACP      Fa0/21(P)   Fa0/22(P)   Fa0/23(P)

                                 Fa0/24(P)

Individual ports inside the EC must agree on this value as well.  When I change the allowed VLAN setting for SW2’s Fast 0/21, that port immediately unbundles.

SW2(config)#int fast 0/21

SW2(config-if)#switchport trunk allowed vlan 200,300

EC-5-CANNOT_BUNDLE2: Fa0/21 is not compatible with Fa0/22

 and will be suspended (vlan mask is different)

EC-5-CANNOT_BUNDLE2: Fa0/21 is not compatible with Fa0/22

 and will be suspended (vlan mask is different)

This is really true of any port attribute, including speed, duplex, and native VLAN. If you change one of those and the EC comes down, you know what to do – change it back!

A few more notes that can save you CCNP exam points and precious troubleshooting time…

• A SPAN source port can be part of an Etherchannel, but not a SPAN destination port.
• Ports in an EC cannot be configured with port security.
• Ports in an EC should have the same native VLAN set.
• If one end of the EC is running in on mode, the other one has to.

And finally — know your LACP and PAgP modes!  The mode doesn’t have to match exactly, but you do have to have LACP or PAgP modes on each side – you can’t have LACP negotiating one side and PAgP negotiating the other, or you’ll never have an Etherchannel.

Thanks once again for making my work a part of your success — Chris B.