Chương 7 - Thực hiện Dịch vụ IP potx

1
Chapter 7 - Implementing
IP Addressing Services
CCNA Exploration 4.0
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Introduction
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DHCP
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Introducing DHCP
 DHCP assigns IP addresses and other important
network configuration information dynamically.
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DHCP Operation
• Manual Allocation: The
administrator assigns a pre-
allocated IP address to the
client and DHCP only
communicates the IP address
to the device.
• Automatic Allocation: DHCP
automatically assigns a static
IP address permanently to a
device, selecting it from a pool
of available addresses. There
is no lease and the address is
permanently assigned to a
device.
• Dynamic Allocation: DHCP
automatically dynamically
assigns, or leases, an IP

address from a pool of
addresses for a limited
period of time chosen by the
server, or until the client tells
the DHCP server that it no
longer needs the address.
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BOOTP and DHCP
• Both DHCP and BOOTP are client/server based and
use UDP ports 67 and 68. Those ports are still known
as BOOTP ports.
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DHCP Message Format
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DHCP Discover
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DHCP Offer
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Configuring a DHCP Server
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Configuring a DHCP Server
Example
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Verifying DHCP
PC1: ipconfig /all
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Verifying DHCP
PC2: ipconfig /all
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Verifying DHCP

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Configuring a DHCP Client
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Configuring a DHCP Client
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DHCP Relay
Host Problem
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DHCP Relay
Host Renew
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DHCP Relay
• Helper address configuration that relays broadcasts to all servers on
the segment.
RTA(config)#interface e0
RTA(config-if)#ip helper-address 172.24.1.255
• But will RTA forward the broadcast?
Broadcast Unicast
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DHCP Relay
• Notice that the RTA interface e3, which connects to the server farm, is not configured
with helper addresses.
• However, the output shows that for this interface, directed broadcast forwarding is
disabled. This means that the router will not convert the logical broadcast
172.24.1.255 into a physical broadcast with a Layer 2 address of FF-FF-FF-FF-FF-
FF.
• To allow all the nodes in the server farm to receive the broadcasts at Layer 2, e3 will
need to be configured to forward directed broadcasts with the following command:
RTA(config)#interface e3
RTA(config-if)#ip directed-broadcast

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DHCP Relay
RTA(config)#interface e0
RTA(config-if)#ip helper-address 172.24.1.255
RTA(config)#interface e3
RTA(config-if)#ip directed-broadcast
L3 Broadcast L2 Broadcast
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Using helper addresses
• By default, the ip helper-address command forwards the eight UDPs services.
• The Cisco IOS provides the global configuration command ip forward-
protocol to allow an administrator to forward any UDP port in addition to the
default eight.
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Configuring a DHCP Server Using SDM
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Configuring a DHCP Server Using SDM
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Verifying and Troubleshooting DHCP