
1 Introduction to the Cisco Broadband Operating System 78-6599-01 04/09/99
Cisco Broadband Operating System User Guide
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The list below defines the terminology used in this chapter.
• Dynamic Host Configuration Protocol (DHCP)—Assigns IP addresses and other
configuration parameters to hosts dynamically. The DHCP protocol is described in RFC
2131, which obsoletes RFC 1541.
• Network Address Translation (NAT)—Converts IP addresses on a private network
(designated as “inside” or “LAN”) to global IP addresses that are valid on another
registered network (designated as “outside” or “WAN”). NAT operates on a router that
connects two or more networks together. Port-level multiplexed NAT is used to translate
all internal private addresses to ports within one or more outside registered IP addresses.
• PPP/Internet Protocol Control Protocol (IPCP)—Dynamically configures IP
addresses over Point-to-Point Protocol (PPP). The Cisco CPE family uses PPP/IPCP to
dynamically negotiate its own registered WAN interface IP address from a central
access server. PPP/IPCP and DHCP are different methods of assigning addresses. The
67x can also be provisioned to obtain its LAN-side (ETH0) address via IPCP.
• DHCP Client—An Internet host using DHCP to obtain configuration parameters such
as a network address.
• DHCP Server—An Internet host that returns configuration parameters to DHCP
clients.
• Inside—The set of network addresses that are subject to conversion by NAT. These
addresses exist on the LAN side of the router.
• Outside—Commonly referred to as legal or global addresses. These addresses exist on
the WAN side of the router.
• Outbound Traffic—Traffic from an inside host to an outside host
• Inbound Traffic—Traffic from an outside host to an inside host.
• Lease Time—The amount of time that an address given to a DHCP client by a DHCP
server remains valid. The lease time can be either:
— A finite lease-time in which the client must renew the lease before it expires in order
to continue using the address.
— An infinite lease-time in which the client maintains the same IP address as long as
it stays connected to the network
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