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Cisco Bug: CSCta24043 - "%IPNAT-4-ADDR_ALLOC_FAIL" message seen when all ports are not allocated

Last Modified

Feb 14, 2018

Products (1)

  • Cisco IOS

Known Affected Releases


Description (partial)


"%IPNAT-4-ADDR_ALLOC_FAILURE: Address allocation failed" message may be seen when there are free ports available in the pool. As a result, you will also see an incorrect half entry in the NAT table which all traffic from this inside local IP will be natted to. 

Pro Inside global      Inside local       Outside local      Outside global
--- <inside_global>:X  <inside_local>:0       ---                ---


The problem is caused by a very specific sequence of NAT allocating and freeing ports. When the problem is triggered, the packet requesting a port for this new entry is generally the first to request a port in the pool.
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