Because there is no stateful synchronization between pairs of redundant gateways, all pool state information is lost in a switchover event. The new gateway creates a new pool with state information for all configured reserved and static address, but has no information about dynamic addresses. When a data-triggered host is authenticated, the pool tries to recreate the lease corresponding with this source IP address. However, this is subject to race conditions. If a data trigger is delayed (for example, the device is not active upon switchover) the DHCP pool may already have assigned the IP address to a new device in the home. This not only blocks the data-trigger for the old device, but may lead to address duplication issues inside the home. To solve this issue, the controller keeps track of allocated dynamic IP addresses. After a switchover event, these addresses can be sent to the vRGW as part of the BRG configuration. In this case, the per-home pool only allocates these addresses to data-triggered devices or DHCP renew triggered devices that request this specific IP address. New devices receive addresses not present on this list. After a configurable timeout, the pool relinquishes any unclaimed IP addresses back to the pool for general use. The currently unclaimed addresses can be displayed using the following command.
show subscriber-mgmt brg gateway brg-id "00:00:5e:00:53:05" standby-ip-addresses
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Bridged Residential Gateway home-aware pool standby IP addresses
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Home-aware pool : 00:00:5e:00:53:05
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192.0.2.10
192.0.2.11
192.0.2.12
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No. of standby IP addresses: 3
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It is recommended to keep the pool state on the controller basic, by marking an address as used when a device is connected and unused when it is disconnected. Periodically, explicitly synchronize the controller with the vRGW to remove addresses for which a device disconnect notification may have been lost.