On Thu, Jun 22, 2023, at 10:42, Kraishak Mahtha wrote:
> I thought if the client sends a request and the server is unable to grant a 
> lease then it can consider an unacked client but here when the client is 
> sending the request to the stand-by server then we are seeing in the log as 
> 
> 2023-06-22 13:36:50.943 DEBUG [kea-dhcp4.ha-hooks/17707.140342512834304] 
> HA_BUFFER4_RECEIVE_NOT_FOR_US [hwtype=1 08:6a:c5:82:de:a8], 
> cid=[01:08:6a:c5:82:de:a8], tid=0xaaba6094: dropping query to be processed by 
> another server
> 
> and is not considered as un-ackedclient, so back to square when can we 
> consider a client request as unacked ?

>From the Kea ARM:

`max-ack-delay` - is one of the parameters controlling partner 
failure-detection. When communication with the partner is interrupted, the 
server examines the values of the “secs” field (DHCPv4) or “elapsed time” 
option (DHCPv6), which denote how long the DHCP client has been trying to 
communicate with the DHCP server. This parameter specifies the maximum time in 
milliseconds for the client to try to communicate with the DHCP server, after 
which this server assumes that the client failed to communicate with the DHCP 
server (is unacknowledged or “unacked”). The default value of this parameter is 
10000.

So in your case, with max-ack-delay set to 10000, a client will need to 
retransmit DISCOVER packets (increasing the "secs" field in the packet each 
time). When the standby server sees a DISCOVER with "secs" higher than 10000, 
for a client that is supposed to be handled by the peer server, it will 
consider that client 'unacked' and increase the unacked-client count.

If the clients do not increase the "secs" field when re-transmitting their 
DISCOVER packets, the HA logic will never consider them 'unacked'.
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