LACP 1:1 Backup


Hello and welcome. Today I’m going to present a feature that you might need and which allow you perform 1:1 backup using LACP.

To start, a brief reminder won’t hurt. LACP refer to Link Aggregation Control Protocol, and it is simply the feature/technology to bundle multiple physical links into one logical link called Port-Channel, with the possibility to perform load sharing across the bundled links.

Ok, let’s jump in. LACP backup 1:1 or what we call in the Cisco world LACP FASTSWITCHOVER, is the feature that allow to have a redundancy between 2 links on the same bundle , by having one Active and one backup. This feature enhance LACP to provide support of fast failover without link flapping.

When this feature is enabled, the Link with the higher priority win the battle and become the active link while the second one remain in standby-hot waiting for a disaster to happen J.

Once there’s a failure on the active link the backup takes over immediately with no impact on the Port-channel. When the active link recover it switch to the active state, and again, without taking the Port-channel down.

Cisco has put some pre-request to activate this feature:

  1. You should have an Etherchannel using LACP (obviously)
  2. The lacp max-bundle should be configured.

This feature is not supported on all switches, I did a search on the Cisco Feature Navigator and unfortunately I had a couple of devices that support it which are:

  • Cisco 7600.
  • Cisco Catalyst 6500.
  • And Cisco ME6524.

On the next post I’ll show how to configure and verify this feature.

I hope this was clear and instructive for you.


10 Responses to LACP 1:1 Backup

  1. Hassan HBAR dit :

    Hi Taoufik,
    First, I want to congratulate this initiative and I wish you good luck and lot of publications.
    Regarding this post, I have two remarks:
    1) which OS version is required. You have mentioned only the hardware.
    2) I didn’t really get what that feature bring LACP we have actif links and backup links. Once an actif link go down a backup link will bring up. Is it convergence time ?
    Hassan HBAR

    • Taoufik BELMEKKI dit :

      Hi Hassan, it is honorable to have the first comment to this post from my Sensei ;).

      i had a quick look on Cisco FN , and i find that this feature is supported starting IOS 12.2IRA to the latest code 15.
      regarding the use of LACP 1:1 backup it is very restricted to the use of two links on LACP etherchannel, so when facing such a situation this can useful and the failover is a WOW ’cause its done immediately. sincerly i didn’t had the chance to calculte the convergenace time with legacy backup.
      i hope i answered your question.

      Thanks again Hassan.

  2. Very clear, and very instructive .

    Thank you.

  3. Mohamed Louhab dit :

    Hi Taoufik

    good job and good initiative

  4. Achraf Harkati dit :

    Thanks for this great initiative, I hope this will be a point for us to exchange our daily experiences and challenges.
    Now is this supported on ASR1K routers and Nexus switchs ?
    For the case of 6500, do we need VSS or can work on two separate independant chassis ?
    Is it backward compatible with legacy 802.3ad; in otherwords can we have one lower end switch (3750 stack that support only legacy 802.3ad for example) on one end of the etherchannel and a two LACP 1:1 Backup cable devices on the other end of the Etherchannel with link in Act/stb?
    In what use case, it would be a good practice to use LACP 1:1; we all know that all Link Agg technologies comes into play when we need to aggregate traffic on more that 1 link while maintaning redundancy, in this case why would we need to have one link Active and the other on standby; it is definitly better than relying on Spanning Tree, but is there other arguments or use cases why I would use LACP with one link Active and the other on stb?

    Thanks again for this great initiave.

    • Taoufik BELMEKKI dit :

      Hi Achraf, Thanks a lot for the motivating comment.
      I’m quite sure this feature is not supported on ASR1K or Nexus referring to the results of Cisco FN (which is 90% believable).
      LACP Fastswitchover will work just fine when using it on only one side (other side legacy 802.3ad) , and Although Cisco says that it should be put on both sides , it works very well and it is functional between a Cisco 7600 (using this feature on two links ) and a Huawei device (with 802.3ad and classic backup).
      this feature can be used to fit your technical need, but i must say the circle of use isn’t as large as other backup methods
      regarding the VSS i don’t see the need of using LACP 1:1 backup with such a design.

  5. Hassan HBAR dit :

    Ssi Taoufik,
    at the end of this post you promised us new posts that mention how to configure and verify this feature.
    shall we wait =) ?
    Thanks a lot

    • Taoufik BELMEKKI dit :

      hi Hassan,

      of course. it is in my drafts, i just have to sit down and right it well. stay tuned.


      Taoufik BELMEKKI

  6. Johnc753 dit :

    Aw, this was a very nice post. In thought I want to put in writing like this moreover taking time and actual effort to make an excellent article but what can I say I procrastinate alot and not at all seem to get something done. kedadefbcccd

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