Timers on vPC peer-keepalive link

[Yan Tian]

Hello,

I am confused about what 2 timer parameters (Keepalive Hold Timeout and Keepalive Timeout) are used for.

Below are the quotes, which are truely quite confusing, from Cisco official docs ( Design and Configuration Guide:

Best Practices for Virtual Port Channels (vPC) on Cisco Nexus 7000 Series Switches)

Keepalive Hold Timeout

This timer gets started once the vPC peer-link goes to down state. During this time period, the secondary vPC peer

device will ignore any peer-keepalive hello messages (or the lack of). This is to assure that network convergence

can happen before any action is taken.

Q1: Why vPC secenary device ignores ongoing keepalive message? As far as I know, secondary device does needs

these keepalive messages to determine subsequent actions (shut down all its vPC memeber port or enter split-brain scenario).

Q2: What kind of network convergence will happen here?

Keepalive Timeout

During this time period, the secondary vPC peer device will look for vPC peer-keepalive hello messages from the

primary vPC peer device. If a single hello is received, the secondary vPC peer concludes that there must be a dual

active scenario and therefore will disable all its vPC member ports (that is, all port-channels that carry the keyword

vpc).

Q1: When will this timer be triggered?

Q2: If a single Hello is received, why dual active scenario (also termed split-brain scenario) is determined?

Q3: Why all vPC member ports on secondary switch will be all disabled when dual active scenario is determined?

Thanks in advance for your help.

[Yan Tian]

Can anyone help pls?

[mingyan]

Q1:keepalive holdtimeout

The difference between the hold-timeout and the timeout parameters is as follows:

• During the hold-timeout, the vPC secondary device does not take any action based on any keepalive messages received, which prevents the system taking action when the keepalive might be received just temporarily, such as if a supervisor fails a few seconds after the peer link goes down

• During the timeout, the vPC secondary device takes action to become the vPC primary device if no keepalive message is received by the end of the configured interval. 

[Vishal Pathak]

keepalive hold-timeout :
-----------------------------
* starts when vpc peer-link goes down.
* during this time period, peer keepalive messages from vpc peer are ignored.
* this is to give the links/vpc peer device time to come back up before any action is taken.

The idea is to give the system some time to recover, before the vpc secondary device takes any action.

keepalive timeout :
------------------------------
* starts at the end of the hold-timeout interval.
* during this time period, the device waits for the peer-keepalive messages.
* If peer-keepalive messages reveiced from the vpc peer, the secondary switch suspends it's vpc member ports and vlans.
* If no peer-keepalive messages received from the vpc peer, the secondary switch now assumes the vpc primary role.