Posted on July 7, 2020 8:35 am
 |  Asked by Naleendra Weerapitiya
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It is clear that for optimal performance MLAG is supposed to be configured with vDS. However, what would be the outcome if MLAG was configured for the relevant ports on the switch side, but each of the host runs with only a standard switch ? Would this result in an undesirable outcome like port toggling ? If it is to work at least in active-standby mode, what are the specifics we have to follow on the host side configuration ( or even switch side configuration ) ?

Posted by Tyler Conrad
Answered on July 7, 2020 7:23 pm

Hi Naleendra,

Yes, there are some cases where placing the vSwitch into an MLAG would be detrimental. In your particular case, leaving the default teaming/load balancing method on the vSwitch will cause the guests to become bound to a specific NIC. This causes some traffic to be blackholed depending on hashing, since only one NIC is active at any point in time for the specific guest (the port-channel will hash to one NIC or the other, depending on the flow - sometimes this hashes to the standby link).

From what I've seen, you have three main options (there may be more, but these are what I've used myself):
1. Run the default load-balancing method (originating virtual port), but don't run an MLAG port-channel down to the ESXi host.
- Pros: No special config needed on the ESXi or Network side.
- Cons: Will utilize the MLAG peer-link more for east/west traffic on the same broadcast domain.
2. Run the IP hash load balancing method, convert both links to active/active, and then toss them in a static port-channel (no lacp).
- Pros: Allows for more efficient bandwidth utilization by using MLAG port-channels (less peer-link at play, fewer 'orphaned' hosts).
- Cons: Tougher to tell if cabling is correct, since you can't rely on the LACP pdus blocking an incorrect attachment; may lead to blackholing if everything isn't as expected physically.
3. Run vDS, and LACP.

Hope this helps,

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