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LAG (LACP) 2 links different speed failover issue

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  • 1.  LAG (LACP) 2 links different speed failover issue

    Posted Aug 25, 2021 11:47 AM

    I am a beginner with Aruba Switches and I trying to configure dynamic LAG (LACP).
    the switches type (JL664A 6300M 24G 4SFP56 Swch) version (ArubaOS-CX Version : FL.10.07.0021)

    the scenario.
    my company has two Links from HQ to ISP MPLS, one main and the other is a backup link, the main link with the speed of 1Gbps and the second one with 100Mbps.

    I tried to configure LAG and it works but the problem is that the two links act on the switch as 1000 Mbps Links but in the real there is one of them support only 100Mbps so when I tried to configure interface speed manually 100Mpbs-Fulldublex and tried to configure the priority for LACP interfaces to use the main Link (1Gbps) in LAG as the LAG speed and the other link to be redundant Link but it works vers as what I want.

    the configuration

    interface lag 1
    no shutdown
    no routing
    vlan trunk native 1
    vlan trunk allowed 300
    lacp mode active
    lacp rate fast
    interface 1/1/1
    no shutdown
    speed 100-full
    lag 1
    lacp port-id 5
    lacp port-priority 5
    interface 1/1/2
    no shutdown
    lag 1
    lacp port-id 10
    lacp port-priority 10

    show commands

    show lacp interfaces

    show lag 1

    I need advice how to make the 1000Mbps Link as the primary
    Note: I tried to configure speed on the main Link as 1000Mbps for testing it denying me

  • 2.  RE: LAG (LACP) 2 links different speed failover issue

    Posted Aug 28, 2021 08:46 AM
    Hi Qais (MITF IT), a LAG - no matter if it is a Non-Protocol (called "Static") or LACP (called "Dynamic") - doesn't correctly form if media speeds of involved member physical links aren't identical (simplifying: LAG doesn't form if you aggregate a 100Mbps+1000Mbps or a 1000Mbps+100Mbps, LAG forms if you aggregate a 100Mbps+100Mbps or 1000Mbps+1000Mbps).

    That's the very basic and essential rule to form a LAG and that is independent by Switch series, Vendor or OS used, it's a requirement due by design.

    IIRC on various Link Aggregation Guides for Aruba CX Switches there is a statement about the above restriction: "Choose the same speed member interfaces while attaching to the LAG. Members with different speed than the already added member do not participate in aggregation for both static and dynamic LAG."

    Also, another ESSENTIAL requirement is that the LAG's member links are co-terminating (ending) on the same physical (or logical, if any) switch where the peer LAG with same characteristic should other terms, you can't pretend a LAG perfectly formed on one device reach a good working state IF its member links aren't co-terminating on a peer device (physical or logical - as in case of virtual switch deployment - it is)...the way you aggregate two or more links together should be the same on both ends of the link.

    Hope this clarify things a bit.

    Davide Poletto

  • 3.  RE: LAG (LACP) 2 links different speed failover issue

    Posted Aug 29, 2021 04:23 AM
    Thanks, Davide

    I understand that the Links should be same
    but I am trying to use the LAG not for expanding the bandwidth, for my scenario the main reason for using it as Link failover

    ٍSince I couldn't use LAG for my scenario could you advise me please if there is another thing I can use to make failover between two links (1000Mbps as the main ) (100Mbps as backup)


  • 4.  RE: LAG (LACP) 2 links different speed failover issue

    Posted Aug 30, 2021 12:06 AM

    From my point of view, you have two options:

    1. if the link need to be a l2 link you are stuck with Spanning Tree
    2. If your link can be a L3 link, and I assume for the connection to your ISP it can, you can work with multi-path routing. I would create two transfer networks to the ISP router and would set different costs for the link (if not set automatically due to the different speeds). If the link with 1Gbps fails it should automatically use the route for the 100Mbps link.

    Florian Baaske
    Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
    Also visit the AirHeads Youtube Channel:
    Feel free to visit my personal Blog

  • 5.  RE: LAG (LACP) 2 links different speed failover issue

    Posted Aug 30, 2021 03:24 AM
    Hi! I agree with Florian, given your scenario you have either one solution or the other (to let a properly configured Spanning Tree feature doing its duty or playing with routing metrics/distances on route(s) of last resort).

    It would be interesting to understand, since you weren't so clear about that, what peer devices your Aruba 6300M switch is connected with...given the Partner's System ID (for the lag1) it looks like - if I'm not mistaken with reported Actor/Partner MAC Addresses - you're playing with another Aruba switch, potentially...and this looks strange because one would think that you're trying to connect your Aruba 6300M directly to ISPs' Routers (ISP Router A: WAN A - LAN A 100Mbps, ISP Router B: WAN B - LAN B 1Gbps) and you want to achieve some sort of links balancing or links failover and you're trying to connect to another Aruba switch.

    Another way is to use Multi-WAN Firewall(s) (it will act as single/redundant Next Hop Gateway for your LAN devices to reach external networks) between your switching infrastructure and your ISPs' Routers, it's a way to move upward your requirement and let the Firewall to perform WAN Links Failover and/or WAN Links Load Balancing, doing so a Transit VLAN - as suggested by Florian above - will continue to be a good approach.

    Davide Poletto