How many PAT we can do with single global IP.

[Pawan Raut]

How many PAT we can do with a single global IP.

ip nat pool NAT-POOL 1.1.1.1 1.1.1.1 netmask 255.255.255.252
ip nat inside source list 101 pool NAT-POOL overload

[Muhammad Awais Khan]

Hi,

Find below about maximum number of translation allowed for PAT but it is theoritical limit. It depends on the platform, NAT session consumes memory so have to take care of the hardware capacity. 

Q. When configuring for PAT (overloading), what is the maximum number of translations that can be created per inside global IP address?

A. PAT (overloading) divides the available ports per global IP address into three ranges: 0-511, 512-1023, and 1024-65535. PAT assigns a unique source port for each UDP or TCP session. It attempts to assign the same port value of the original request, but if the original source port has already been used, it starts scanning from the beginning of the particular port range to find the first available port and assigns it to the conversation. 

Reference: https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/26704-nat-faq-00.html

[Muhammad Zahid]

In PAT source port number used for maintaining the uniqueness of a session can have a value from 0 to 65535, there can be a theoretical maximum of 65536 PAT entries at a time for each inside global address. Since each NAT entry requires about 160 bytes of memory, the number of translations possible is limited by the amount of memory available on the router.