I have 3 switches soon to be setup in topology as shown below switches

I have a fibre link and LAN cable directly connecting switch1 and switch3 and also another connection going from switch1 to switch3 via switch2 using LAN cables.

I want to have Link Aggregation Group(LAG) at switch1 for the 3 ports (2 directly connecting to switch3 and one through intermediate switch2) for getting higher bandwidth and failover redundancy for switch3.

Q1- Is it possible to have LAG with the indirect connection through switch2 as shown in the figure?

Q2- How would I configure LAG for ports @ switch1? (If you point me to exact commands or any resources links, it would be helpful)

Q3- Do I need to configure LAG @ switch3 also for corresponding ports?

Q4- What modes(active/passive/on) should I use for LACP @ switch1 and @switch3?

1 Answer 1


Q1: This requires MLAG (multichassis LACP) to work. You can't split and splice a simple static or LACP trunk.

Q2: As far as I know, SG500X and SG300 don't support MLAG. You can configure a LAG trunk for the two lines between S1 and S3 though and use STP(Spanning Tree Protocol) to take care of the looping links to S2.

Q3: LAG trunks need to be configured on both terminating switches.

Q4: Use LACP whenever possible; static trunking should only be used when LACP isn't possible.

  • thanks for the quick reply. LACP has 2 modes right? active and passive. What modes should I use at S1 and S3? if I'm not mistaken one should be active and one should be passive or both should be active. Does it matter which of these switches is configured for active or passive LACP?
    – jaggi
    Dec 17, 2017 at 20:24
  • At least one side requires active negotiation. With both sides on passive, the trunk won't come up. I use active on both sides.
    – Zac67
    Dec 17, 2017 at 20:26
  • need clarification, in Q2 by ` two lines` you mean 1 fibre and 1 ether?
    – jaggi
    Jan 29, 2018 at 6:17
  • @jaggi Yes - the PHY doesn't matter. LAG links are required to use the same speed though.
    – Zac67
    Jan 29, 2018 at 7:31
  • Cisco SG500X-24 has 1Gbps ethernet port and 10Gbps fibre port. What needs to be done in this case?
    – jaggi
    Jan 29, 2018 at 7:42

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