Question

What happens when a NAT pool exhausts?

Solution

When a NAT pool exhausts, a session is dropped and Analytics raises an alarm.

NAT does not re-evaluate the policy for next matching rule. This implies that, after the NAT rule/policy is hit, it will try to allocate resources from that pool.    

Currently Versa Flex VNF doesn't maintain the failure reason per session when a NAT session (policy/rule/session) fails, because it is a rare scenario with automatic port selection scheme. 

Run the show debug cgnat counters internal CLI command to know the reason for NAT failure.

 Example

admin@BRANCH1002-B1002-cli> show debug cgnat counters internal
 CGNAT_CNTR_FIRST_PACKET               6739
 CGNAT_CNTR_SESS_INTEREST              440997
 CGNAT_CNTR_SESS_REEVAL                48
 CGNAT_CNTR_SESS_REEVAL_SKIP           48
 CGNAT_CNTR_SESS_ACCEPT                6739
 CGNAT_CNTR_SESS_IGNORE                434305
 CGNAT_CNTR_SESS_CLOSE                 6739
 CGNAT_CNTR_BINDINGS_ALLOCD            6739
 CGNAT_CNTR_BINDINGS_FREED             6739
 CGNAT_CNTR_SKIP_BCAST_MCAST           322028

Troubleshoot: Define multiple pools with different pool range in Rule.