MLAG health check message configuration

[Renne_Stuart]

How and where do you configure MLAG health check message config? I have read in the Exos userguide 15_7 that this is now a feature however it does not give to much information on how and where to configure this. Has anyone configured this and had it working? Is this feature available in summitX-15.5.3.4-patch1-5.xos or do i need to upgrade to get this feature?

(page 278 of userguide)
"Starting in ExtremeXOS 15.5, health check messages can also be exchanged on an alternate path byseparate configuration – typically the “Mgmt” VLAN. If the peer is alive when the ISC link alone goes down, one of the MLAG peers disables its MLAG ports to prevent duplicate south-bound traffic to the remote node. To reduce the amount of traffic on the alternate path, health check messages are initiated on the alternate path only when the ISC link goes down. When the ISC link is up, no health check messages are exchanged on the alternate path.

When the MLAG switch misses 3 consecutive health check messages from the peer, it declares that the MLAG peer is not reachable on the ISC link. It then starts sending out health check messages on the alternate path to check if the peer is alive. When the first health check message is received from the MLAG peer on the alternate path, it means that the peer is alive. In this scenario, one of the MLAG peersdisables its MLAG ports to prevent duplication of south-bound traffic to the remote node.

Note
The MLAG switch having the lower IP address for the alternate path VLAN disables its ports.

When the ISC link comes up and the switch starts receiving health check messages on the ISC control VLAN, the ports that were disabled earlier have to be re-enabled. This action is not performed immediately on the receipt of the first health check message on the ISC control VLAN. Instead the switch waits for 2 seconds before enabling the previously disabled ports. This is done to prevent frequent enabling and disabling of MLAG ports due to a faulty ISC link up event.

[StephenW]

https://documentation.extremenetworks.com/exos_16/EXOS_16_2/Slots_and_Ports/c_interswitch-communicat...

It’s in the Note in that page. 

[TheTrueElling]

Is this verified or stated somewhare in documention, that it is the switch with the lowest IP on the interface used to reach the peer via alternate path that will disable its MLAG ports?
Or is it the ip of the ISC vlan interface?

/ Elling 

[Stephane_Grosj1]

I'd like to stress out a few things, following Oscar's comment:

- indeed, the role of the alternate path is to use... an alternate physical path. So it makes no sense to have it configured if it follows the same path (both physical - the same cable - than "geographical" - the same conduit). You want to be sure a cable fault or an accidental "cut" will not have the same impact on that alternate path.

- if you use the Mgmt network for it, which seems a natural thing to do, there's one caveat you need to be aware of: if someone issue a "disable port all" on the mlag peer having the higher IP address, it will not affect the Mgmt port, and so the mlag peer with the lowest IP address would disable its ports as well, leading in a bad situation.

[OscarK]

The alternate path should not go over the same ISC link that the mlag peers are already using. Normally if you use the vr-MGMT ports you could use those IP addresses for alternate path. If you want to use another vlan be sure that vlan does not span the ISC ports.