CCNA Guide to Cisco Networking - Chapter 9 Key Terms

lookup

The process of retrieving an IP address for a given name and providing it to the client that requested it.

overlapping

When an organization wants to connect to the Internet, but its internal addressing scheme is registered to another entity. Instead of renumbering the internal network, the organization uses NAT to translate its internal addressing scheme to the addresses that it was assigned by the ISP.

DHCP REQUEST

A formal request for IP configuration information intended for a specific DHCP server but broadcast so that all servers can see the association.

port forwarding

A method for sending packets from an external host system through a firewall or NAT router to an internal device. In this way, the internal device IP address is hidden from the external network, yet the internal device can still service requests from the external network.

network address translation (NAT)

A method for using a router to separate an internal network from an external network (usually the Internet), which is defined in RFC 3022. Internal hosts with private or unregistered IP addresses can effectively use one or more public registered IP addresses to communicate with external systems.

DHCP DISCOVER

A packet that is broadcast on bootup by a client when that client has no IP information or incomplete IP information.

port address translation (PAT)

A process used in overloading that allows multiple internal, unregistered IP addresses to use a single external registered address.

overloading

A type of NAT that allows multiple internal hosts to use one or more external IP addresses. The NAT router uses a table to keep track of the IP addresses and ports of each host, dynamically mapping each internal socket to a valid external socket.

static NAT

A type of network address translation (NAT) that allows for a one-to-one mapping of internal to external addresses. One internal address is mapped to one specific external address.

dynamic NAT

A type of network address translation in which the valid external IP addresses to be mapped to internal addresses are floating or not fixed. The NAT router can then dynamically assign any of the available external addresses to any of the hosts on the internal network.

DHCP ACK

A unicast acknowledgement sent by the DHCP server to the client.

DHCP OFFER

A unicast reply by a DHCP server to a client that has broadcast a DHCP DISCOVER packet.

DNS

Domain Name Services provides name-to-IP address translation so that users can use names instead of addresses in commands.

DHCP

Dynamic Host Configuration Protocol provides IP configuration information to clients when they bootup.

bindings

IP to MAC address mappings that are found in the DHCP database.

DHCP relay

If no DHCP service is found on the network, the router can be configured to relay the request to a DHCP server on a different network.