Dynamic NAT is similar to static NAT in that the NAT router creates a one-to-one mapping between an
inside local and inside global address and changes the IP addresses in packets as they exit and enter the
inside network. However, the mapping of an inside local address to an inside global address happens
dynamically. Dynamic NAT accomplishes this by setting up a pool of possible inside global addresses and
defining criteria for the set of inside local IP addresses whose traffic should be translated with NAT.
With dynamic NAT, you can configure the NAT router with more IP addresses in the inside local address
list than in the inside global address pool. When the number of registered public IP addresses is defined in
the inside global address pool, the router allocates addresses from the pool until all are allocated. If a new
packet arrives, and it needs a NAT entry, but all the pooled IP addresses are already allocated, the router
discards the packet. The user must try again until a NAT entry times out, at which point the NAT function
works for the next host that sends a packet. This can be overcome through the use of Port Address
Translation (PAT).