Cisco 7246VXR - uBR Router Software Configuration Manual page 78

Supported Software Features for the Cisco uBR7200 Series
DHCP, Time of Day (ToD) and TFTP Servers
The Cisco uBR7200 series routers support onboard Dynamic Host Configuration Protocol (DHCP)
servers, Time of Day (ToD) and TFTP servers. This allows the Cisco uBR7200 series routers to provide
cable modems with IP address information, to supply an RFC 868-compliant time-of-day timestamp, and
to download a DOCSIS configuration file, without requiring separate and external servers.
A DOCSIS-compliant cable modem requires access to three types of servers in order to successfully
come online:
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The Dynamic Host Configuration Protocol (DHCP) is a network management features that simplifies CMTS
provisioning. DHCP provides configuration parameters to Internet hosts. DHCP consists of two components:
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DHCP is built on a client/server model, where designated DHCP server hosts allocate network addresses
and deliver configuration parameters to dynamically configured hosts. DHCP supports three
mechanisms for IP address allocation:
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The Cisco IOS DHCP server feature is a full DHCP server implementation that assigns and manages IP
addresses from specified address pools within the router to DHCP clients. If the Cisco IOS DHCP server
cannot satisfy a DHCP request from its own database, it can forward the request to one or more
secondary DHCP servers defined by the network administrator.
You can configure a DHCP server in the following ways:
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DOCSIS 1.1 Quality of Service Features
DOCSIS 1.1 modifies the DOCSIS 1.0 specification to provide better performance, in particular for
real-time traffic such as voice calls. The DOCSIS 1.1 specification provides several functional
enhancements over DOCSIS 1.0 coaxial cable networks.
DOCSIS 1.1 features are supported in the Cisco IOS 12.2 BC release train, with additional DOCSIS 1.1
features being supported in certain earlier Cisco IOS 12.1 EC and 12.0 SC release trains.
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The first is a DHCP server, which provides the cable modem with an IP address, a subnet mask and
other IP related parameters.
The second is an RFC868 compliant
current time is. A cable modem needs to know the time in order to be able to properly add accurate
timestamps to its event log.
The third is a Trivial File Transfer Protocol (TFTP) server from which a cable modem is able to
download a DOCSIS configuration file containing cable modem specific operational parameters.
a protocol for delivering host-specific configuration parameters from a DHCP server to a host
a mechanism for allocating network addresses to hosts
Automatic allocation—DHCP assigns a permanent IP address to a client.
Dynamic allocation—DHCP assigns an IP address to a client for a limited period of time (or until
the client explicitly relinquishes the address).
Manual allocation—The network administrator assigns an IP address to a client and DHCP is used
simply to convey the assigned address to the client.
You can configure the DHCP server when using the Cable Interface Setup facility. For additional
information, refer to the "Configuring the Cisco uBR7200 Series Using the Setup Facility" section
on page 2-17.
You can configure DHCP services alone, or when configuring ToD and TFTP services. For
additional information, refer to the chapter titled "Configuring DHCP, ToD, and TFTP Services" in
the Cisco Cable Modem Termination System Feature Guide
Chapter 1
Time-of-Day Server which lets the modem know what the
on Cisco.com.
Overview of Cisco uBR7200 Series Software
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