Re: Design reasons for LACP active versus on

There is a tradeoff to consider. When configuring channels for
optimum performace, on/on is the preferred method because the channel
doesn't have to be negotiated, which would tune several seconds out of
convergence. However, as mentioned, this leaves the door open for STP
loops due to misconfigurations or hardware failures. So you would
have to make the judgment call for performance or safety.

The question was about configuring channels connecting to a 3rd party
server though, and not between two switches. I would agree with the
suggested on/on option as the connected server such as an ESX host
isn't running STP, but there may be cases where you would want to run
LACP when connecting to these types of devices.

For example, say that you have a 2G channel between two 6509s across a
DWDM ring. Each switch connects to an ONS mux locally, so if you have
a DWDM failure and your channels are configured on/on, the channel
will stay up. You need a polling mechanism to bring the channel down.
 With default LACP configuration it can take 90 seconds to bring the
channel down, but this can be tuned down to a few seconds with LACP
rate fast.

You could potentially have the same issue if you connect two switches
through a blade system, etc. connected in passthru or bridge mode.
Basically the answer is "it depends," and the specific application and
convergence requirements need to be considered.

On 5/12/09, Chris Breece <cbreece1_at_gmail.com> wrote:
> I've created spanning tree loops using "on". LACP has some sanity checking
> built in to prevent this.
>
> For instance, a typical access layer switch plugged into two distribution
> switches all connected via layer 2. Configure the following
>
> access layer switch:
>
> *int po1*
> *switchport trunk encap dot1q*
> *switchport mode trunk*
> **
> *int gi1/1*
> *switchport trunk encap dot1q*
> *switchport mode trunk*
> *channel-group 1 mode on*
> **
> *int gi1/2
> *
> *switchport trunk encap dot1q*
> *switchport mode trunk*
> *channel-group 1 mode on*
>
>
> Now plug gi1/1 into distro switch 1, and gi1/2 in distro switch 2.
>
> Watch the network explode :P
>
> LACP would err-disable the ports in this scenario.
>
>
>
> Chris
>
>
>
> On Tue, May 12, 2009 at 6:48 AM, Thameem Maranveetil Parambath <
> tparamba_at_thecontactcentre.ae> wrote:
>
> > If you configure statically (on), the negotiation time can be saved. So I
> > would go for (on) rather than active or desirable.
> >
> >
> >
> >
> > Marc La Porte <marc.a.laporte_at_gmail.com>
> > Sent by: nobody_at_groupstudy.com
> > 12/05/2009 02:46 PM
> > Please respond to
> > Marc La Porte <marc.a.laporte_at_gmail.com>
> >
> >
> > To
> > Cisco certification <ccielab_at_groupstudy.com>
> > cc
> >
> > Subject
> > Design reasons for LACP active versus on
> >
> >
> >
> >
> >
> >
> > Hi,
> >
> > From a design viewpoint, configuring LACP (L2 Etherchannel) from an access
> > switch (6500) to a third-party server (IBM, HP, etc) would it be better to
> > configure our side as "active" or as "on"?
> >
> > Thanks
> > Marc
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > The content of this email together with any attachments, statements
> > and opinions expressed herein contains information that is private
> > and confidential and intended for the named addressee(s) only. If
> > you are not the addressee of this email you may not copy, forward,
> > disclose or otherwise use it or any part of it in any form
> > whatsoever. If you have received this message in error please
> > notify postmaster_at_etisalat.ae by email immediately and delete the
> > message without making and copies.
> >
> >
> > Blogs and organic groups at http://www.ccie.net
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

-- 
Ronald Angello
CCIE 17846
CCDP, CCIP, CCNP
Blogs and organic groups at http://www.ccie.net