How to configure HSL in MAS

Aruba Employee
Aruba Employee

What is HSL ??


What is HSL ??





  • Hot-standby-Link (HSL) contains 2 links: primary or active link and secondary or standby link.
  • If the primary or the active link goes down, the secondary link automatically starts forwarding data traffic.
  • Data traffic is forwarded only on the active link. While data traffic is blocked on secondary link, layer-2 control traffic is still permitted on it.
  • When the primary interface becomes operationally up and secondary interface is active, the traffic is not switched to primary unless the preemption mode is set to forced.

Points to remember before configuring HSL. 



•Spanning tree (MSTP and PVST+) must be disabled, before configuring HSL.
          HSL and spanning tree can not be configured on the same system at the same time.

                   (ArubaS3500-24P) (config) #interface gigabitethernet 0/0/22

                   (ArubaS3500-24P) (gigabitethernet "0/0/22") #backup interface gigabitethernet 0/0/23

                   Error: MSTP is enabled in the system. Disable MSTP to configure HSL interfaces


•HSL is a 1:1 ratio for primary and backup pairs.
–One backup interface can not be the backup of multiple primary interfaces.
–An interface can be part of only one HSL pair.
•HSL links are always trusted.
•Primary and backup interfaces must have the same switching profile.
•You cannot configure HSL backup interface on port-channel member interfaces. They should be configured on port-channel itself
•The interfaces cannot be tunnel-node interfaces.
•Remote end ports on are not aware of HSL configured on local box












•HSL can be configured directly in the interface. First, on the primary interface (0/0/22), specify the back-up interface (0/0/23):


(config) #interface gigabitethernet 0/0/22

(gigabitethernet "0/0/22") #backup interface gigabitethernet 0/0/23

•Pre-emption can be configured if necessary. By default it is turned off:

(gigabitethernet "0/0/22") #preemption mode forced

(gigabitethernet "0/0/22") #preemption delay 10






#show interface-config gigabitethernet 0/0/22

gigabitethernet "0/0/22"


Parameter                        Value

---------                        -----

<output truncated>

HSL Backup interface             gigabitethernet0/0/23

HSL Interface Preemption Mode    FORCED

HSL Interface Preemption Delay   10


#show hot-standby-link

HSL Interfaces Info


Primary   State   Backup    State    Last Switchover Time

--------  ------  -------   ------   --------------------

GE0/0/22  Active  GE0/0/23  Standby  2012-02-17 05:09:34 (PST)



#show hot-standby-link gigabitethernet 0/0/22

HSL Interface Info


Primary Interface: GE0/0/22 (Active)             Backup Interface:  GE0/0/23 (Standby)

Preemption Mode: FORCED                          Preemption Delay: Timer Not Active

Last Switchover Time: 2012-02-17 05:09:34 (PST)  Flap Count: 2


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Last update:
‎07-08-2014 02:05 PM
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