Network address translation

 NAT maps Private IPs to Public IPs.
 A short term solution to the problem of the depletion of IP addresses
 It is required because of shortage of IPv4 Address.
 Whatever connects directly into Internet must have public (globally
unique) IP address
 So Private IP addresses can be used within a private network
 Three address ranges are reserved for private usage
10.0.0.0/8
172.16.0.0/16 to 172.31.0.0/16
192.168.0.0/24 to 192.168.255.0/24
 A private IP is mapped to a Public IP, when the machine has to
access the Internet

 NAT is a router function where IP addresses (and possibly port
numbers) of IP datagram's are replaced at the boundary of a private
network
 NAT is a method that enables hosts on private networks to
communicate with hosts on the Internet.
 NAT is run on routers that connect private networks to the public
Internet, to replace the IP address-port pair of an IP packet with
another IP address-port pair.

 When you need to connect to the Internet and your hosts don’t have
globally unique IP addresses.
 When you’ve changed to a new ISP that requires you to renumber
your network.
 When you need to merge two intranets with duplicate addresses

Names Meaning
Inside Local Source host inside address before translation typically
an RFC 1918 address
Outside Local Address from which source host is known on the
Internet. This is usually the address of the router
interface connected to ISP—the actual Internet address.
Inside Global Source host address used after translation to get onto
the Internet. This is also the actual Internet address.
Outside
Global
Address of outside destination host. The real
Internet address.

 Dynamic Translation (IP Masquerading)
 Static Translation
 Load Balancing Translation
 Network Redundancy Translation

 Network Address and Port Translation (NAPT)
 Map an unregistered IP address to a registered IP address from out
of a pool of registered IP addresses.
 large number of internal users share a single external address.
 NAT only prevents external hosts from making connections to
internal hosts.

 Allow one-to-one mapping between local and global addresses.
 A block external addresses are translated to a same size block of
internal addresses
◦ Firewall just does a simple translation of each address.
 Port forwarding - map a specific port to come through the Firewall
rather than all ports.
 Useful to expose a specific service on the internal network to the
public network

 Maps multiple unregistered IP addresses to a single registered IP
address (many-to-one) by using different source ports.
 Port Address Translation (PAT) which is also commonly referred to
as NAT Overload.
 PAT allows you to permit thousands of users to connect to the
Internet using only one real global IP address.
 Only works for stateless protocols (like HTTP)

 Multiple internet connections are attached to a NAT Firewall that it
chooses.
 Uses based on bandwidth, congestion and availability.
 Can be used to provide automatic fail-over of servers or load
balancing.
 Firewall is connected to multiple ISP with a masquerade for each
ISP and chooses which ISP to use based on client load
 kind of like reverse load balancing
 Adead ISP will be treated as a fully loaded one and the client will
be routed through another ISP.

 Scenario: Corporate network has many hosts but only a small
number of public IP addresses.

 NAT solution:
 Corporate network is managed with a private address space.
 NAT device, located at the boundary between the corporate
network and the public Internet, manages a pool of public IP
addresses.
 When a host from the corporate network sends an IP datagram to
a host in the public Internet, the NAT device picks a public IP
address from the address pool, and binds this address to the
private address of the host.

 Scenario: In CIDR, the IP addresses in a corporate network are
obtained from the service provider. Changing the service provider
requires changing all IP addresses in the network.

 NAT solution:
 Assign private addresses to the hosts of the corporate network.
 NAT device has static address translation entries which bind the
private address of a host to the public address.
 Migration to a new network service provider merely requires an
update of the NAT device. The migration is not noticeable to the
hosts on the network.
Note:
 The difference to the use of NAT with IP address pooling is that
the mapping of public and private IP addresses is static.

 Scenario: Single public IP address is mapped to multiple hosts in a
private network.

 NAT solution:
 Assign private addresses to the hosts of the corporate network.
 NAT device modifies the port numbers for outgoing traffic.

 Scenario: Balance the load on a set of identical servers, which are
accessible from a single IP address

 NAT solution:
 Here, the servers are assigned private addresses.
 NAT device acts as a proxy for requests to the server from the
public network.
 The NAT device changes the destination IP address of arriving
packets to one of the private addresses for a server.
 A sensible strategy for balancing the load of the servers is to
assign the addresses of the servers in a round-robin fashion.

 Increases flexibility when connecting to the Internet.
 Eliminates address renumbering as a network evolves.
 Remedies address overlap events.
 Conserves legally registered addresses.

1. H.323, CUSeeMe, VDO Live – video teleconferencing
applications
2. Xing – Requires a back channel
3. Rshell – used to execute command on remote Unix machine
– back channel
4. IRC – Internet Relay Chat – requires a back channel
5. PPTP – Point-to-Point Tunneling Protocol
6. SQLNet2 – Oracle Database Networking Services
7. FTP – Must be RFC-1631 compliant to work
8. ICMP – sometimes embeds the packed address info in the
ICMP message
9. IPSec – used for many VPNs
10. IKE – Internet Key Exchange Protocol
11. ESP – IP Encapsulating Security Payload

 Hardware and software firewalls.
 Routers.
 Proxy servers
 RAS server that is a simple router/firewall

Network address translation

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (18)

Similar to Network address translation

Similar to Network address translation (20)

Recently uploaded

Recently uploaded (20)

Network address translation