When NAT pool configuration changed and service-set where this pool is called is not deactivated/re-activated properly, some sessions may stuck in NAT subscriber extension table. This causes traffic outage for subscriber when it starts traffic as NAT port block is not allocated properly.

In problematic scenario SRC_ALLOC_FAIL and SRC_ALLOC_POOL_NOT_FOUND counter will be growing in output of 'show usp nat counters' shell command for corresponding service PIC:

FLOWD_SPC3-2.0(vty)# show usp nat counters
   <snip>
   SRC_ALLOC_FAIL                   7
   SRC_ALLOC_POOL_NOT_FOUND         7

NAT subscriber extension table will contain stale entry for problematic subscriber which can be checked with 'cprod -A fpcX.picY -c "show usp nat subscriber-extension"' shell command. Example of problematic entry show bellow:

sset  pvt_ip     pub_ip     state eim ports sess flag    cpu pool

0x7  2001:DB8:0:0:0:0:0:0 192.0.2.1 0   0  8   0   0xc00   26 0x1000005

Modifying NAT pool configuration is considered as a catastrophic change. After changing NAT pool it's recommended to deactivate service-set, wait when all NAT subscriber extension entry get deleted and re-activate service-set afterwards.