Explain the following terms as used in the context of Network Address Translation:

Question

1. Static NAT
2. Dynamic NAT
3. NAT with IP overload
4. Port address translations
5. IP masquerading

Answer 1

1. The static address translation can be used translate between IP networks that have the same size (contain the same number of IPs). A special case is when both networks contain just one IP, i.e. the net
mask is 255.255.255.255. Implementation wise, the strategy is quite easy to implement and can be achieved using the following logic transformation:
new-address = new-network OR (old-address AND (NOT netmask)).
In addition, no information about the state of connections that are being translated needs to be kept, looking at each IP packet individually is sufficient. Connections from outside the network to inside hosts are no problem, they just appear to have a different IP than on the inside, so static NAT is (almost) completely transparent.
2. A dynamic NAT can be used to map many IP addresses onto some or a single IP address. This allows the individual networks to increase their internal address space without asking for more global IP addresses. Each new connection from the inside gets assigned an IP address from the pool of external addresses, as long as there are unused addresses left.
3. "Overload" refers to a situation in which no more free IP addresses are available from the pool and ports have to be assigned to distinguish two different connections.
4. Port Address Translation (PAT) allows many-to-one address mapping, since many inside IP addresses can be mapped to one outside IP address. The port number (TCP or UDP) is sufficient to ensure that packets are delivered properly.
5. This is an extreme case of address translation where a multiple number of IP addresses map onto just a single IP address. For each outgoing packet the source IP address is replaced by the router’s (external) IP address, and the source port is exchanged against an unused port from the range reserved
exclusively for masquerading on the router. If the destination IP of an incoming packet is the local router IP and the destination port is inside the range of ports used for masquerading on the router, the NAT router checks its masquerading table if the packet belongs to a masqueraded session; if this is the case, the destination IP and port of the internal host is inserted and the packet is sent to the internal host.