Network Redundancy with LACP Trunking












1















I would like to set up a redundant link between two switches. I have four ports available to accomplish this.



Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2.



Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They are plugged into Switch 2 Ports 1+2.



In Scenario B I can unplug one of the patch cables and the switches will still be linked, establishing redundancy. In Scenario A, what will happen when I unplug one of the patch cables? Will LACP allow the link over just one interface? Or will the link stop because an interface is missing.










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    I would like to set up a redundant link between two switches. I have four ports available to accomplish this.



    Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2.



    Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They are plugged into Switch 2 Ports 1+2.



    In Scenario B I can unplug one of the patch cables and the switches will still be linked, establishing redundancy. In Scenario A, what will happen when I unplug one of the patch cables? Will LACP allow the link over just one interface? Or will the link stop because an interface is missing.










    share|improve this question









    New contributor




    jbakerj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      1












      1








      1








      I would like to set up a redundant link between two switches. I have four ports available to accomplish this.



      Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2.



      Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They are plugged into Switch 2 Ports 1+2.



      In Scenario B I can unplug one of the patch cables and the switches will still be linked, establishing redundancy. In Scenario A, what will happen when I unplug one of the patch cables? Will LACP allow the link over just one interface? Or will the link stop because an interface is missing.










      share|improve this question









      New contributor




      jbakerj is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.












      I would like to set up a redundant link between two switches. I have four ports available to accomplish this.



      Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are plugged into Switch 2 ports 1+2.



      Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They are plugged into Switch 2 Ports 1+2.



      In Scenario B I can unplug one of the patch cables and the switches will still be linked, establishing redundancy. In Scenario A, what will happen when I unplug one of the patch cables? Will LACP allow the link over just one interface? Or will the link stop because an interface is missing.







      switch switching spanning-tree redundancy ieee-802.1ax






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      share|improve this question









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      edited 1 hour ago









      Ron Maupin

      63.7k1366120




      63.7k1366120






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      asked 1 hour ago









      jbakerjjbakerj

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          2 Answers
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          Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are
          plugged into Switch 2 ports 1+2.




          Both links will be used, but a single flow will only use one link. There is a hashing algorithm that determines which flow uses which link. If one of the links goes down, then all the traffic will be switched to the other link. This happens very rapidly.




          Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They
          are plugged into Switch 2 Ports 1+2.




          They will not actually be trunked together. STP will block one link because it creates a single, loop-free path to the root bridge. When the active link goes down, STP will switch over to the redundant link, but this happens fairly slowly; a few seconds for RSTP, and up to 50 seconds for standard STP.






          share|improve this answer































            1














            From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is redundant. An LACP trunk set up with eight ports works with anything between one to eight physical links - so does a static trunk.



            The difference is that an LACP trunk only works when both sides negotiate the aggregation. Without successful negotiation the physical links fall apart into separate logical links. Usually, it's combined with a spanning tree protocol to avoid bridge loops - without STP the bridge loop would bring down the network.



            In contrast, in a static trunk the links are aggregated when they're up. The switch doesn't check whether the trunk makes sense. You could use links terminated differently and you'd get weird and possibly unexpected effects.



            Generally, LACP trunks are safer to use. You should only use static trunks when LACP isn't available.



            Of course, the combination of LACP and STP calls for a better integrated solution that even works with multiple switches and meshed setups. This is what Shortest Path Bridging aka IEEE 802.1aq is for. Sadly it hasn't caught on in the mid-range class yet.






            share|improve this answer























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              2 Answers
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              oldest

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              2 Answers
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              active

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              active

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              2















              Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are
              plugged into Switch 2 ports 1+2.




              Both links will be used, but a single flow will only use one link. There is a hashing algorithm that determines which flow uses which link. If one of the links goes down, then all the traffic will be switched to the other link. This happens very rapidly.




              Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They
              are plugged into Switch 2 Ports 1+2.




              They will not actually be trunked together. STP will block one link because it creates a single, loop-free path to the root bridge. When the active link goes down, STP will switch over to the redundant link, but this happens fairly slowly; a few seconds for RSTP, and up to 50 seconds for standard STP.






              share|improve this answer




























                2















                Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are
                plugged into Switch 2 ports 1+2.




                Both links will be used, but a single flow will only use one link. There is a hashing algorithm that determines which flow uses which link. If one of the links goes down, then all the traffic will be switched to the other link. This happens very rapidly.




                Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They
                are plugged into Switch 2 Ports 1+2.




                They will not actually be trunked together. STP will block one link because it creates a single, loop-free path to the root bridge. When the active link goes down, STP will switch over to the redundant link, but this happens fairly slowly; a few seconds for RSTP, and up to 50 seconds for standard STP.






                share|improve this answer


























                  2












                  2








                  2








                  Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are
                  plugged into Switch 2 ports 1+2.




                  Both links will be used, but a single flow will only use one link. There is a hashing algorithm that determines which flow uses which link. If one of the links goes down, then all the traffic will be switched to the other link. This happens very rapidly.




                  Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They
                  are plugged into Switch 2 Ports 1+2.




                  They will not actually be trunked together. STP will block one link because it creates a single, loop-free path to the root bridge. When the active link goes down, STP will switch over to the redundant link, but this happens fairly slowly; a few seconds for RSTP, and up to 50 seconds for standard STP.






                  share|improve this answer














                  Scenario A: Switch 1 has ports 1+2 trunked together via LACP. They are
                  plugged into Switch 2 ports 1+2.




                  Both links will be used, but a single flow will only use one link. There is a hashing algorithm that determines which flow uses which link. If one of the links goes down, then all the traffic will be switched to the other link. This happens very rapidly.




                  Scenario B: Switch 1 has ports 1+2 trunked together without LACP. They
                  are plugged into Switch 2 Ports 1+2.




                  They will not actually be trunked together. STP will block one link because it creates a single, loop-free path to the root bridge. When the active link goes down, STP will switch over to the redundant link, but this happens fairly slowly; a few seconds for RSTP, and up to 50 seconds for standard STP.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 1 hour ago









                  Ron MaupinRon Maupin

                  63.7k1366120




                  63.7k1366120























                      1














                      From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is redundant. An LACP trunk set up with eight ports works with anything between one to eight physical links - so does a static trunk.



                      The difference is that an LACP trunk only works when both sides negotiate the aggregation. Without successful negotiation the physical links fall apart into separate logical links. Usually, it's combined with a spanning tree protocol to avoid bridge loops - without STP the bridge loop would bring down the network.



                      In contrast, in a static trunk the links are aggregated when they're up. The switch doesn't check whether the trunk makes sense. You could use links terminated differently and you'd get weird and possibly unexpected effects.



                      Generally, LACP trunks are safer to use. You should only use static trunks when LACP isn't available.



                      Of course, the combination of LACP and STP calls for a better integrated solution that even works with multiple switches and meshed setups. This is what Shortest Path Bridging aka IEEE 802.1aq is for. Sadly it hasn't caught on in the mid-range class yet.






                      share|improve this answer




























                        1














                        From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is redundant. An LACP trunk set up with eight ports works with anything between one to eight physical links - so does a static trunk.



                        The difference is that an LACP trunk only works when both sides negotiate the aggregation. Without successful negotiation the physical links fall apart into separate logical links. Usually, it's combined with a spanning tree protocol to avoid bridge loops - without STP the bridge loop would bring down the network.



                        In contrast, in a static trunk the links are aggregated when they're up. The switch doesn't check whether the trunk makes sense. You could use links terminated differently and you'd get weird and possibly unexpected effects.



                        Generally, LACP trunks are safer to use. You should only use static trunks when LACP isn't available.



                        Of course, the combination of LACP and STP calls for a better integrated solution that even works with multiple switches and meshed setups. This is what Shortest Path Bridging aka IEEE 802.1aq is for. Sadly it hasn't caught on in the mid-range class yet.






                        share|improve this answer


























                          1












                          1








                          1







                          From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is redundant. An LACP trunk set up with eight ports works with anything between one to eight physical links - so does a static trunk.



                          The difference is that an LACP trunk only works when both sides negotiate the aggregation. Without successful negotiation the physical links fall apart into separate logical links. Usually, it's combined with a spanning tree protocol to avoid bridge loops - without STP the bridge loop would bring down the network.



                          In contrast, in a static trunk the links are aggregated when they're up. The switch doesn't check whether the trunk makes sense. You could use links terminated differently and you'd get weird and possibly unexpected effects.



                          Generally, LACP trunks are safer to use. You should only use static trunks when LACP isn't available.



                          Of course, the combination of LACP and STP calls for a better integrated solution that even works with multiple switches and meshed setups. This is what Shortest Path Bridging aka IEEE 802.1aq is for. Sadly it hasn't caught on in the mid-range class yet.






                          share|improve this answer













                          From a functional point of view, there's no difference between LACP trunks and static trunks. All links are aggregated (with the limitations Ron has already pointed out) and the aggregation group is redundant. An LACP trunk set up with eight ports works with anything between one to eight physical links - so does a static trunk.



                          The difference is that an LACP trunk only works when both sides negotiate the aggregation. Without successful negotiation the physical links fall apart into separate logical links. Usually, it's combined with a spanning tree protocol to avoid bridge loops - without STP the bridge loop would bring down the network.



                          In contrast, in a static trunk the links are aggregated when they're up. The switch doesn't check whether the trunk makes sense. You could use links terminated differently and you'd get weird and possibly unexpected effects.



                          Generally, LACP trunks are safer to use. You should only use static trunks when LACP isn't available.



                          Of course, the combination of LACP and STP calls for a better integrated solution that even works with multiple switches and meshed setups. This is what Shortest Path Bridging aka IEEE 802.1aq is for. Sadly it hasn't caught on in the mid-range class yet.







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 18 mins ago









                          Zac67Zac67

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