Upon the recovery of the failed MS-ISA, all existing subscribers that are affected by the bypass continue to use the bypass. However, all new subscribers that come online after the recovery, are automatically L2-Aware NAT’d (and therefore do not use the bypass).
Restoring bypassed subscribers to the L2-Aware NAT after the recovery, requires manual intervention by the operator. This is accomplished by executing the tools> perform>nat>recover-l2aw-bypass slot/mda command:
In L2-Aware NAT, the <subscriber to outside IP, port-block> mappings are allocated during the subscriber attachment phase (when the subscriber comes online) and are maintained in the CPM. Therefore, they are preserved in the CPM during MS-ISA failure. This means that the original mappings for the recovered subscribers continue to be used when the MS-ISA is recovered.
Be aware that only the partial mappings <subscriber to outside IP, port-block> are preserved. This does not include preservation of NAT sessions sometimes referred as fully qualified flows. NAT sessions are maintained in MS-ISA and they are lost during MS-ISA failures. Hence, this model provides stateless failover to an external NAT node.
The operator is notified about the MS-ISA failure by a log message or an SNMP trap. An example of such log is:
9 2017/06/07 11:32:49.748 UTC MINOR: NAT #2020 Base NAT
"The NAT MDA 5/1 is now inactive in group 2."