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20193 Views 9 Replies Latest reply: Apr 24, 2014 12:30 AM by venky RSS

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Port channel best practices mode on or desirable w/pagp

Mar 27, 2009 9:09 PM

SpongeRob 81 posts since
Jul 8, 2008

 

Hello again,

 

 

With regards to port channels/ether channels - I had to create on this eve for a remote site and my thoughts were to keep it simple and use channel-group 1 mode on;

 

 

rather than

 

 

channel-group 1 mode desirable non-silent

channel-protocol pagp

 

 

Please advise -

 

 

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,398 posts since
    Oct 7, 2008

     

    Well.. Is "on" a representation of PAgP?

     

     

    If you want things really to be negotiated then "desirable" is your best bet. If you want to be more in control yourself, then "on" is your best bet.

     

     

    HTH,

     

     

    Scott

     

     

     

     

     

  • Jochen Bartl 24 posts since
    Nov 13, 2008

     

    Sometimes you have to use "mode on", for example when you connect a NetApp filer to a catalyst switch. NetApp filers don't support PAgP or LACP afaik.

     

     

    best regards,

     

     

    jochen

     

     

  • Jared 5,502 posts since
    Jul 27, 2008

     

    I have always used mode on in my etherchannel configs. That way I know that I have control over it and don't rely on the gear to negotiate their channels. Also, when hooking up VM hosts, you may find that they don't support any negotiation protocols and you will have no choice but to use mode on.

     

     

    Just my opinion.

     

     

  • Brian 2,968 posts since
    Aug 17, 2009

    Aloha SpongeRob,

     

    If you use just the command "channel-group 1 mode on", if your switch is capable of both PAgP and LACP, it will not "know" which protocol to use.  See the following output.

     

    Switch_A(config)#int range f0/1 - 2
    Switch_A(config-if-range)#channel-group 3 mode on
    Creating a port-channel interface Port-channel 3

    Switch_A(config-if-range)#end
    Switch_A#sh
    00:12:47: %SYS-5-CONFIG_I: Configured from console by console
    Switch_A#sh etherchannel
                    Channel-group listing:
                    ----------------------

     

    Group: 3
    ----------
    Group state = L2
    Ports: 2   Maxports = 8
    Port-channels: 1 Max Port-channels = 1
    Protocol:    -

    Switch_A#

     

    Notice the Protocol field is just a dash.  When using the "on" for the mode, you must also use the "channel-protocol" command to tell the swicth which protocl to use.

     

    So, if you wanted to keep it simple the following would have worked with the minimal amount of configuration in the switches.

     

    Switch_A(config)#int range f0/21 - 22
    Switch_A(config-if-range)#channel-group 1 mode desirable
    Creating a port-channel interface Port-channel 1

    Switch_A(config-if-range)#end
    Switch_A#

    Switch_A#sh etherchannel
                    Channel-group listing:
                    ----------------------

    Group: 1
    ----------
    Group state = L2
    Ports: 2   Maxports = 8
    Port-channels: 1 Max Port-channels = 1
    Protocol:   PAgP

     

    HTH

  • Brian 2,968 posts since
    Aug 17, 2009

    Aloha Jared,

     

    Using the mode "desirable" in its default (which is silent) will allow a switch to still form an Etherchannel with devices that do not participate in PAgP, such as file servers or network analyzers.

     

    HTH

  • Flooter 2 posts since
    Oct 23, 2010

    http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.1E/native/configuration/guide/channel.html#wp1033712

    You can configure EtherChannels manually or you can use the Port Aggregation Control Protocol (PAgP) or, with Release 12.1(13)E and later, the Link Aggregation Control Protocol (LACP) to form EtherChannels. The EtherChannel protocols allow ports with similar characteristics to form an EtherChannel through dynamic negotiation with connected network devices.

     

    on

    Mode that forces the LAN port to channel unconditionally. In the on mode, a usable EtherChannel exists only when a LAN port group in the on mode is connected to another LAN port group in the on mode. Because ports configured in the on mode do not negotiate, there is no negotiation traffic between the ports. You cannot configure the on mode with an EtherChannel protocol.

     

    in my understanding mode "on" means "it just works".

     

    PAgP and LACP are just negotiation protocols, they are not "link aggregation protocols" therefore they don't describe nor set any kind of standarts for doing aggregation process.

  • stall 1 posts since
    Apr 29, 2009

    Just looking at this and I agree with Flooter.  PagP and LACP are only negotiation protocols as far as I can see

  • venky 1 posts since
    Apr 24, 2014
    Currently Being Moderated
    9. Apr 24, 2014 12:30 AM (in response to stall)
    Re: Port channel best practices mode on or desirable w/pagp

    what i noticed during an implementation is that the manual mode of setting "on" has a chance of blackholing the traffic, when one of the link is unidirectional.

    so do not forget to enable udld when you use mode on

     

    Thanks

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