VPC Peer-Link and LACP Rate Fast

[luke.smith]

Hi,

As per best practice I believe on your VPC Peer-Link you should be running LACP for better failure detection etc.

Now as a general rule I always configure "lacp rate fast" when running LACP to help detect issues sooner and removed from the Port-Channel.

Can you confirm if running "lacp rate fast" is a good move on the Peer-Link

Thanks

Luke

[Alexey Prilutskiy]

Yep, you can use fast lacp hello on peer link

[jg.vink01]

Hi Luke,

I think you are right. .

"

You can configure the LACP rate fast feature on the LACP ports of a Cisco Nexus 5000 Series switch or a Cisco Nexus 2000 Series Fabric Extender that is connected to a Cisco Nexus 5000 Series switch.

The LACP rate fast feature is used to set the rate (once every second) at which the LACP control packets are sent to an LACP-supported interface. The normal rate at which LACP packets are sent is 30 seconds.

"

I'm only not sure, how it will act when the connection is flapping. I think that 1 second is not an issue.

Below an answer from another forum:

"

An LACP PDU is around 110 bytes, so running them every second isn't likely to even register on an Ethernet link of any speed.

I would recommend running in "fast" mode at all times for rapid detection of faults.

"

Greetz.

Jeroen

[Jevgeni Rõžov]

The difference between slow and fast LACP modes is the delay between sending hello packets. 30 and 1 seconds respectively. In theory fast LACP mode allows way much faster failure detection of a peer device.

My advice would be to use the LACP fast mode for the Peer-Link on short distances because one of the peers might theoretically end up in a state when the interfaces are up, but the traffic is not being processed. In that case you will most possibly have a 1-30sec traffic disruption.

[Juan Leon]

I have a customer who configured a port-channel connecting a Core VDC to an OTV VDC, the port-channel will flap at both ends mentioning that the partner is delayed with the LACP PDU.

For the peer-link I have found that it is not recommended using LACP fast rate.

The defect ID is CSCuu91089, please give it a look.