This feature provides support for 1:1 inter WLAN-GW active-backup redundancy. The failure detection and switchover mechanism is contained in WLAN-GWs, and there is no dependency on the AP to detect failure of WLAN-GW and switch traffic to tunnel endpoint on a different WLAN-GW. There is also no dependency on NAT or a particular type of NAT on WLAN-GW. If local DHCP servers are used for address allocation, then DHCP leases in the server are synchronized to the backup WLAN-GW via MCS. However, ESM state for the UE is created on the backup WLAN-GW based on data-triggered authentication after switchover. The granularity of switchover is subscriber-interface. Both WLAN-GWs are required to be configured with the same tunnel endpoint address. Also, the subscriber interfaces on both WLAN-GW must be configured with the same subnets. Only the WLAN-GW that is deemed as active announces the tunnel endpoint address in routing toward the APs.
Active-backup decision is based on monitor and export route concept (same as what is used with NAT redundancy). Monitor and export routes are configured on the subscriber-interface on both WLAN-GWs. These should be complementary with respect to the ones on the other WLAN-GW. When WLAN-GW group goes up operationally, check is made in the FDB for presence of monitor route (which is the route exported by the other WLAN-GW). If it is not found, then the WLAN-GW assumes active state with respect to ownership of the tunnel end-point address, and the tunnel end-point address is announced in IGP toward the AP (subject to configured IGP and routing policy). The active WLAN-GW also announces the aggregate subscriber subnets upstream in routing. When WLAN-GW group comes up operationally, and detects the monitor route in the FDB, it assumes standby state with respect to the tunnel endpoint address. It does not announce the tunnel endpoint or the subscriber subnets in routing.
Each WLAN-GW needs to track the monitor route in the FDB. If the monitor route is no longer in the FDB, and the WLAN-GW is in standby state, it transitions to active, and announce the tunnel end-point toward APs, and subscriber subnets upstream. This draws the traffic from the AP to the backup WLAN-GW. Redundancy is non-revertive. The monitor and export routes are configured on the subscriber-interface.
config>service>ies>sub-if
wlan-gw
redundancy
[no] export <ip-prefix/length>
[no] monitor <ip-prefix/length>
exit
exit
If the number of operationally up WLAN-GW IOMs in wlan-gw group drops below the number of active IOMs configured, the WLAN-GW group is brought down (based on the oper-down-on-group-degrade command under the WLAN-GW interface), and switchover procedures for the subscriber-interface are triggered (export route, tunnel endpoint address and subscriber subnets are withdrawn from routing).
config>service>vprn>sub-if>grp-if
config>service>ies>sub-if>grp-if
wlan-gw
[no] oper-down-on-group-degrade
The switchover can also be triggered administratively on per subscriber-interface basis using the tools perform command.
*A:vsim-07-cpm# tools perform wlan-gw redundancy force-switchover service <service-id> interface <ip-int-name>