13. ARP, DHCP
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ICND1 v1.04-1
DHCP AND ARP
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Understanding DHCP
DHCP is built on a client-server model, as follows:
oThe DHCP server hosts allocate network addresses and
deliver
configuration parameters.
oThe term "client" refers to a host requesting
initialization
parameters from a DHCP server.
DHCP supports these three mechanisms for IP address
allocation:
oAutomatic allocation; DHCP assigns a permanent IP address to
a
client.
oDynamic allocation; DHCP assigns an IP address to a client for
a
limited period of time.
oManual allocation; A client IP address is assigned by the
network
administrator, and DHCP is used simply to convey the
assigned
address to the client.
Dynamic allocation is the only that allows automatic reuse of
an
address that is no longer needed by the client to which it
was
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DHCP
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Using a Router as a DHCP Server
Cisco IOS Software includes a full DHCP server
implementation:
Assigns IP addresses from specified address pools within the
router
Can be configured to assign the IP address of these
components:
oDomain Name System (DNS) server
oDefault router
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DHCP Server Using a Router
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Additional Tasks
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DHCP Pool
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Checking the DHCP Configuration
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DHCP Pool Status
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ARP operation
197.15.22.33
A.B.C.1.3.3
197.15.22.35
A.B.C.7.3.5
197.15.22.34
A.B.C.4.3.4
A B C
ARP Table:
? MACA.B.C.1.2.3
MAC
?
IP197.15.22.33
IP197.15.22.35
Data
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ARP operation:ARP request
MAC
A.B.C.1.3.3
MAC
ff.ff.ff.ff.ff.ff
IP197.15.22.3
3
IP197.15.22.3
5
What is your MAC Addr?
197.15.22.33
A.B.C.1.3.3
197.15.22.35
A.B.C.7.3.5
197.15.22.34
A.B.C.4.3.4
A B C
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ARP operation:Checking
MAC
A.B.C.1.3.3
MAC
ff.ff.ff.ff.ff.ff
IP197.15.22.3
3
IP197.15.22.3
5
What is your MAC Addr?
197.15.22.33
A.B.C.1.3.3
197.15.22.35
A.B.C.7.3.5
197.15.22.34
A.B.C.4.3.4
A B C
That is my IP !
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ARP operation:ARP reply
MAC
A.B.C.1.3.3
MAC
ff.ff.ff.ff.ff.ff
IP197.15.22.3
3
IP197.15.22.3
5
What is your MAC Addr?
197.15.22.33
A.B.C.1.3.3
197.15.22.35
A.B.C.7.3.5
197.15.22.34
A.B.C.4.3.4
A B C
ARP Reply
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ARP operation:Caching
MAC
A.B.C.1.3.3
MAC
A.B.C.7.3.
5
IP197.15.22.3
3
IP197.15.22.3
5
Data
197.15.22.33
A.B.C.1.3.3
197.15.22.35
A.B.C.7.3.5
197.15.22.34
A.B.C.4.3.4
A B C
ARP Table:
A.B.C.7.3.5 197.15.22.35
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