The support for interchassis stateless High Availability (HA) results in an existing DHCP session to appear as unclassified IP session. The subscriber is unaware about the reboot of iWAG on the device and continues to send data packets thereby creating an unclassified IP session. After half lease time, the subscriber may send a unicast renew which removes the existing session and creates a new DHCP session. Therefore it is mandatory to keep the existing session and continue the service to the subscriber unless the subscriber reappears on different service set identifier (SSID) or reboot and send discover packet.

On receiving the DHCP control packets, iWAG validates the packets against any existing unclassified session. If an unclassified session is found, iWAG validates the subnet of both the existing session and the DHCP control packet. If the subnets match, iWAG will update the existing session from unclassified MAC to DHCP session creating a DHCP binding.

Note	In case of any discrepancy, iWAG will bring down the existing unclassified session, discarding the DHCP control packet as well.

The following figure and the subsequent steps describes a call flow pertaining to a Ethernet over GRE (EoGRE): intra-chassis stateless HA.

Figure 1. E0GRE: Inter-Chassis Stateless HA Call Flow

1. IP session is established on iWAG when a subscriber device connects to network through open or secure SSID.

   1a. Session establishment through Open SSID

   1b. Session establishment through Secure SSID

2. In case of a fail over, session is re-established on the standby iWAG.

   2a. Coverts subscriber from existing IP session to DHCP session.