12 Replies Latest reply: Oct 11, 2012 12:41 AM by Julian RSS

    Port-channel configuration

    Julian

      Hi everyone,

       

      I have a question about the configuration of etherchannels. I have seen many configurations to set etherchannels in texts books, examples, etc. In all of them, they set the switchport mode (access, trunk or dynamic auto/desirable) under the physical interfaces, but not under the port-channel interface. But my CCNP Switch Lab Manual says "Configure the logical interface to become a trunk by first entering the interface port-channel number command and then the switchport mode trunk command." For example:

       

      ALS1(config)# interface port-channel 1

      ALS1(config-if)# switchport mode trunk

       

      I believe this applies to every mode (access, trunk or dynamic auto/desirable). So, it seems you have to configure the desired switchport mode under both the physical interfaces and the port-channel interface. I have tried some configurations in Packet Tracer and it depends of the switchport mode. Sometimes this is not needed because the switchport mode configured under the physical interfaces is automatically copied in the running-config under the port-channel interface, but sometimes not. Also this depends of the switch model (2960, 3560). Because Packet Tracer is not 100% reliable I would like to know if it is necessary or not, maybe any of you have practical skills on this or real switches and can shed some light on this.

      Any answer will be much appreciated.

       

      Regards,

      Julián

        • 1. Re: Port-channel configuration
          DelVonte

          Hello Julian,

           

          You are correct, it depends on switch model, and it may also depend on IOS. Either way, on real equipment you will know pretty quickly if the commands are successful.

           

          That being said, you can safely assume on cisco exams that you will go with how it works on the 3560. Also, as long as the configuration is consistent across the ports and the channel, the channel should form. However, it is better to minimally configure the ports, create the channel, add the ports to the channel, and perform the configuration on the channel. At least this has been my experience.

           

          In addition, all future config changes should occur on the channel, and not the member ports.

           

          Regards

          DelVonte

          • 2. Re: Port-channel configuration
            Julian

            Hi DelVonte,

             

            Thank you for your contribution. For the last part

             

            In addition, all future config changes should occur on the channel, and not the member ports.


            I understand, for instance, that if the ports and the channel are set to trunk mode and now I want to change the trunk mode for the channel to dynamic auto, I should set the port-channel to dynamic auto and leave the physical ports in trunk mode. But this does not seem very consistent accross the ports and the channel. Did you mean that?

             

            Regards,

            Julián

            • 3. Re: Port-channel configuration
              cadetalain

              Hi,

               

              the member interfaces should take the config from the port-channel.

               

              Regards.

               

              Alain

              • 4. Re: Port-channel configuration
                Najaf

                Hi Julian,

                 

                With my previous experience with port-channel i must say that they are very much addict to the sequence of configuration (in what order you configure the port channel). I had instance in much port channel never came up until i followed below procedure.

                 

                1) shut the interfaces which you want to include in port-channel

                2) apply port-channel group under interfaces

                3) configure the port-channel setting

                4) enable the interface range.

                 

                With this all interface will get the configuration applied on the port-channel. A typical configuration is shown below.

                 

                conf terminal

                interface range fas 0/1-10

                shut

                channel-group 1 mode on

                !

                int port-channel 1

                switchport

                switchport access vlan 111

                switchport mode access

                !

                interface range fas 0/1-10

                no shut

                !

                 

                Hope this helps.

                 

                Regards

                 

                Najaf

                • 5. Re: Port-channel configuration
                  Julian

                  Hi Najaf,

                   

                  Useful contribution. Only one more thing, is the line switchport trunk encapsulation dot1q a typo? Because in that example the channel will form as an access port for vlan111 and it seems that line will not take any effect.

                   

                  Regards,

                  Julián

                  • 6. Re: Port-channel configuration
                    Najaf

                    Sorry Julian,

                     

                    It was a typo...I have corrected this now. Thanks for pointing this out...

                     

                    Regards

                     

                    Najaf

                    • 7. Re: Port-channel configuration
                      Julian

                      Hi Najaf,

                       

                      Ok, now it makes more sense

                      Thank you, I did not know that the member interfaces get the configuration applied on the port-channel, as you and also Alain indicate.

                      Thanks to all

                       

                      Regards,

                      Julián

                      • 8. Re: Port-channel configuration
                        ijlal.tech

                        Hi Najaf,

                         

                        There are some rules that has to be followed when configuring etherchannel.

                         

                        first configure the physical interfaces with switchport mode trunk, then apply channel-protocol and last channel-group, the moment you will end with this configuration you will see logical interface of port-channel with blank only interface port-channel 1 will be written in show running-config, after going under port-channel first configure trunk encapsulation then trunk mode, channel protocol , channel-group and after that whateven vlans you will add in logical interface of port-channel will automatically inserted into physical port of etherchannel, you will have clearly seenable.

                         

                        Regards,

                         

                        M Ijlal Ahmed.

                        • 9. Re: Port-channel configuration
                          Najaf

                          Hi Ijlal,

                           

                          Thanks for sharing this...

                           

                          What ever i have shared in my previous post has always worked for me. It is good to know that there are various methods to achive the same goal :-)

                           

                          Regards

                           

                          Najaf

                          • 10. Re: Port-channel configuration
                            Julian

                            Hi Ijlal,

                             

                            I do not totally agree with that. The physical interfaces do not have to be trunk ports, they can be access ports. Channel-protocol is an optional command, the protocol can be set with the channel-group command, it does not make sense to use again the channel-protocol and channel-group commands under the port-channel interface.

                             

                            Regards,

                            Julián

                            • 11. Re: Port-channel configuration
                              Dmcneil

                              @julian

                               

                              I think it depends on the version of IOS that's running on the switch. Some of them require a channel-protocol command and some don't.

                              • 12. Re: Port-channel configuration
                                Julian

                                @dmcneil

                                 

                                Maybe, I am not an expert on Etherchannels. But I have seen many examples using only the channel-group command (mandatory) and without the channel-protocol command. There are more post related to this

                                 

                                https://learningnetwork.cisco.com/thread/24826?start=0&tstart=0

                                (Brian answer)

                                 

                                https://supportforums.cisco.com/thread/31387

                                (At the end)

                                 

                                Regards,

                                Julián