Failover for environment with mostly mobile devices

[Hillary Nelson]

Our DHCP server serve great number of mobile devices(iPhone, Android) with
15 minutes lease time, during peak time we see 200 ACK/second.

Those mobile devices tend to ignore the lease time and broadcast DISCOVER
every couple of minutes regardless the lease time.  I wonder how failover
works
for devices with very short lease and mostly do discover instead of renew.

For example an iPhone got a lease from server1, then server1 fails,  will
the failover peer server2 be able to assign the same lease assigned by
server1 to the client if iPhone sends DISCOVER instead of renew, or server2
will offer a brand new lease from its own pool? I know server2 can renew
existing server1's lease(without manually put it to partner-down state),
but what happens for DISCOVER from a device with an existing valid lease?

Any help will be greatly appreciated!

Hillary
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