CCNA2 LS CH11
What is NAT? - Answer NAT has many uses, but its primary use is to conserve public
IPv4 addresses. It does this by allowing networks to use private IPv4 addresses
internally and providing translation to a public address only when needed. NAT has an
added benefit of adding a degree of privacy and security to a network, because it hides
internal IPv4 addresses from outside networks.
NAT-enabled routers - Answer can be configured with one or more valid public IPv4
addresses. These public addresses are known as the NAT pool. When an internal
device sends traffic out of the network, the NAT-enabled router translates the internal
IPv4 address of the device to a public address from the NAT pool. To outside devices,
all traffic entering and exiting the network appears to have a public IPv4 address from
the provided pool of addresses. A NAT router typically operates at the border of a stub
network.
A stub network - Answer is a network that has a single connection to its neighboring
network, one way in and one way out of the network.
NAT includes four types of addresses: - Answer Inside local address
Inside global address
Outside local address
Outside global address
Inside address - Answer The address of the device which is being translated by NAT.
Outside address - Answer The address of the destination device.
Local address - Answer A local address is any address that appears on the inside
portion of the network.
Global address - Answer A global address is any address that appears on the outside
portion of the network.
Inside local address - Answer The address of the source as seen from inside the
network.
Inside global address - Answer The address of source as seen from the outside
network.
Outside global address - Answer The address of the destination as seen from the
outside network. It is a globally routable IPv4 address assigned to a host on the
Internet. Most often the outside local and outside global addresses are the same.
, Outside local address - Answer The address of the destination as seen from the inside
network. While uncommon, this address could be different than the globally routable
address of the destination.
Static address translation (static NAT) - Answer One-to-one address mapping between
local and global addresses.
Dynamic address translation (dynamic NAT) - Answer Many-to-many address mapping
between local and global addresses.
Port Address Translation (PAT) - Answer Many-to-one address mapping between local
and global addresses. This method is also known as overloading (NAT overloading).
Static NAT - Answer uses a one-to-one mapping of local and global addresses. These
mappings are configured by the network administrator and remain constant.
Static NAT is particularly useful for web servers or devices that must have a consistent
address that is accessible from the Internet, such as a company web server. It is also
useful for devices that must be accessible by authorized personnel when offsite, but not
by the general public on the Internet.
Static NAT requires that enough public addresses are available to satisfy the total
number of simultaneous user sessions.
Dynamic NAT - Answer uses a pool of public addresses and assigns them on a first-
come, first-served basis. When an inside device requests access to an outside network,
dynamic NAT assigns an available public IPv4 address from the pool. dynamic NAT
requires that enough public addresses are available to satisfy the total number of
simultaneous user sessions.
Port Address Translation (PAT) - Answer Also known as NAT overload, maps multiple
private IPv4 addresses to a single public IPv4 address or a few addresses. This is what
most home routers do. The ISP assigns one address to the router, yet several members
of the household can simultaneously access the Internet. This is the most common form
of NAT.
With PAT, multiple addresses can be mapped to one or to a few addresses, because
each private address is also tracked by a port number. When a device initiates a TCP/IP
session, it generates a TCP or UDP source port value to uniquely identify the session.
When the NAT router receives a packet from the client, it uses its source port number to
uniquely identify the specific NAT translation.
PAT ensures that devices use a different TCP port number for each session with a
server on the Internet. When a response comes back from the server, the source port
number, which becomes the destination port number on the return trip, determines to
which device the router forwards the packets. The PAT process also validates that the
incoming packets were requested, thus adding a degree of security to the session.
What is NAT? - Answer NAT has many uses, but its primary use is to conserve public
IPv4 addresses. It does this by allowing networks to use private IPv4 addresses
internally and providing translation to a public address only when needed. NAT has an
added benefit of adding a degree of privacy and security to a network, because it hides
internal IPv4 addresses from outside networks.
NAT-enabled routers - Answer can be configured with one or more valid public IPv4
addresses. These public addresses are known as the NAT pool. When an internal
device sends traffic out of the network, the NAT-enabled router translates the internal
IPv4 address of the device to a public address from the NAT pool. To outside devices,
all traffic entering and exiting the network appears to have a public IPv4 address from
the provided pool of addresses. A NAT router typically operates at the border of a stub
network.
A stub network - Answer is a network that has a single connection to its neighboring
network, one way in and one way out of the network.
NAT includes four types of addresses: - Answer Inside local address
Inside global address
Outside local address
Outside global address
Inside address - Answer The address of the device which is being translated by NAT.
Outside address - Answer The address of the destination device.
Local address - Answer A local address is any address that appears on the inside
portion of the network.
Global address - Answer A global address is any address that appears on the outside
portion of the network.
Inside local address - Answer The address of the source as seen from inside the
network.
Inside global address - Answer The address of source as seen from the outside
network.
Outside global address - Answer The address of the destination as seen from the
outside network. It is a globally routable IPv4 address assigned to a host on the
Internet. Most often the outside local and outside global addresses are the same.
, Outside local address - Answer The address of the destination as seen from the inside
network. While uncommon, this address could be different than the globally routable
address of the destination.
Static address translation (static NAT) - Answer One-to-one address mapping between
local and global addresses.
Dynamic address translation (dynamic NAT) - Answer Many-to-many address mapping
between local and global addresses.
Port Address Translation (PAT) - Answer Many-to-one address mapping between local
and global addresses. This method is also known as overloading (NAT overloading).
Static NAT - Answer uses a one-to-one mapping of local and global addresses. These
mappings are configured by the network administrator and remain constant.
Static NAT is particularly useful for web servers or devices that must have a consistent
address that is accessible from the Internet, such as a company web server. It is also
useful for devices that must be accessible by authorized personnel when offsite, but not
by the general public on the Internet.
Static NAT requires that enough public addresses are available to satisfy the total
number of simultaneous user sessions.
Dynamic NAT - Answer uses a pool of public addresses and assigns them on a first-
come, first-served basis. When an inside device requests access to an outside network,
dynamic NAT assigns an available public IPv4 address from the pool. dynamic NAT
requires that enough public addresses are available to satisfy the total number of
simultaneous user sessions.
Port Address Translation (PAT) - Answer Also known as NAT overload, maps multiple
private IPv4 addresses to a single public IPv4 address or a few addresses. This is what
most home routers do. The ISP assigns one address to the router, yet several members
of the household can simultaneously access the Internet. This is the most common form
of NAT.
With PAT, multiple addresses can be mapped to one or to a few addresses, because
each private address is also tracked by a port number. When a device initiates a TCP/IP
session, it generates a TCP or UDP source port value to uniquely identify the session.
When the NAT router receives a packet from the client, it uses its source port number to
uniquely identify the specific NAT translation.
PAT ensures that devices use a different TCP port number for each session with a
server on the Internet. When a response comes back from the server, the source port
number, which becomes the destination port number on the return trip, determines to
which device the router forwards the packets. The PAT process also validates that the
incoming packets were requested, thus adding a degree of security to the session.
