Transcript Module 09 Presentation

Cisco Systems CCNA Version 3 Semester 1
Module 9
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 1
Students completing this module should be able to:
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Explain why the Internet was developed and how TCP/IP fits the
design of the Internet.
List the four layers of the TCP/IP model.
Describe the functions of each layer of the TCP/IP model.
Compare the OSI model and the TCP/IP model.
Describe the function and structure of IP addresses.
Understand why subnetting is necessary.
Explain the difference between public and private addressing.
Understand the function of reserved IP addresses.
Explain the use of static and dynamic addressing for a device.
Understand how dynamic addressing can be done using RARP, BootP
and DHCP.
Use ARP to obtain the MAC address to send a packet to another
device.
Understand the issues related to addressing between networks.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 2
Module Overview
9.1 Introduction to TCP/IP
9.1.1 History and future of TCP/IP
9.1.2 Application layer
9.1.3 Transport layer
9.1.4 Internet layer
9.1.5 Network access layer
9.1.6 Comparing the OSI model and the TCP/IP model
9.1.7 Internet architecture
9.2 Internet Addresses
9.2.1 IP addressing
9.2.2 Decimal and binary conversion
9.2.3 IPv4 addressing
9.2.4 Class A, B, C, D, and E IP addresses
9.2.5 Reserved IP addresses
9.2.6 Public and private IP addresses
9.2.7 Introduction to subnetting
9.2.8 IPv4 versus IPv6
9.3 Obtaining an IP Address
9.3.1 Obtaining an Internet address
9.3.2 Static assignment of an IP address
9.3.3 RARP IP address assignment
9.3.4 BOOTP IP address assignment
9.3.5 DHCP IP address management
9.3.6 Problems in address resolution
9.3.7 Address Resolution Protocol (ARP)
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 3
Overview
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9.1.1 History and future of TCP/IP
The Department of Defense (DoD) developed the TCP/IP reference model to
provide a communication network that could continue to function in wartime.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 5
9.1.6 Comparing the OSI model and the TCP/IP model
Both have an application layer.
Both have similar transport and network layers.
Both assume packet-switched networks.
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9.1.2 Application layer
OSI layers 5, 6 & 7 are all rolled into the TCP Application Layer.
Encoding
Data
Presentation
Dialog
Control
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 7
1.
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3.
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5.
6.
7.
File Transfer Protocol (FTP)
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FTP is a reliable, connection-oriented service that uses TCP to transfer files
between systems that support FTP.
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It supports bi-directional binary file and ASCII file transfers.
Trivial File Transfer Protocol (TFTP)
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TFTP is a connectionless service that uses the User Datagram Protocol (UDP).
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TFTP is used on the router to transfer configuration files and Cisco IOS
images, and to transfer files between systems that support TFTP.
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It is useful in some LANs because it operates faster than FTP in a stable
environment.
Network File System (NFS)
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NFS is a distributed file system protocol suite developed by Sun Microsystems
that allows file access to a remote storage device such as a hard disk across a
network.
Simple Mail Transfer Protocol (SMTP)
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SMTP administers the transmission of e-mail over computer networks.
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It does not provide support for transmission of data other than plaintext.
Terminal emulation (Telnet)
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Telnet provides the capability to remotely access another computer.
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It enables a user to log in to an Internet host and execute commands.
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A Telnet client is referred to as a local host.
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A Telnet server is referred to as a remote host.
Simple Network Management Protocol (SNMP)
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SNMP is a protocol that provides a way to monitor and control network devices,
and to manage configurations, statistics collection, performance, and security.
Domain Name System (DNS)
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DNS is a system used on the Internet for translating names of domains and
their publicly advertised network nodes into IP addresses.
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9.1.3 Transport layer
There are only two protocols at the transport layer, TCP and UDP.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 9
9.1.3 Transport layer
Note: The first line is not sent.
The second line is the ACK line.
TCP
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is responsible for:
end-to-end communication
flow control
reliability of data delivery
TCP supports a logical connection between the sending and receiving hosts
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 10
9.1.3 Transport layer
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9.1.4 Internet layer
The
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IP Protocol is responsible for:
routing packets to remote hosts
defining packets
transferring data between the internet layer and the network access layer
It provides control and messaging capabilities:
eg. Ping, “Destination Unreachable” etc.
ARP & RARP also act at the network layer
(They relate MAC & IP addresses)
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 12
9.1.1 History and future of TCP/IP
IPv4
IPv6
In 1992 the standardization of a new generation of IP, often called IPng, was supported by
the Internet Engineering Task Force (IETF).
IPng is now known as IPv6.
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9.1.4 Internet layer
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9.1.5 Network access layer
A NETWORK ACCESS problem could be caused by any of these protocols.
SLIP Serial Line Internet Protocol
PPP
Point to Point Protocol
FDDI Fiber Distributed Data Interface
ATM Asynchronous Transfer Mode
SMDS Switched Multimegabit Data Service
(They relate MAC & IP addresses)
The Network Access Layer supports BOTH LAN and WAN technologies
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 15
9.1.5 Network access layer
The Network Access Layer is considered to be
the host-to-network layer of the TCP/IP model.
…and leaves at the
Network Layer (packet).
The data comes in to the NIC
at the Physical Layer (Frame)…
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 16
9.1.6 Comparing the OSI model and the TCP/IP model
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9.1.7 Internet architecture
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A network of networks is called an internet, indicated with the lowercase “i”.
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When referring to the networks that developed from the DoD on which the
Worldwide Web (www) runs, the uppercase “I” is used and is called the Internet.
192.168.1.0
192.168.2.0
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 18
9.1.7 Internet architecture
192.168.2.0
192.168.1.0
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192.168.3.0
The router keeps a list of all networks, but leaves the local delivery
details to the local physical networks.
In this situation, the routers pass messages to other routers.
Each router shares information about which networks it is connected to.
This builds the routing table.
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9.1.7 Internet architecture
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9.1.7 Internet architecture
192.168.2.0
192.168.1.0
192.168.3.0
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 21
“Scale-Free Networks”
Scientific American
May 2003
The internet somewhere
in the N.E. US
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 22
9.2.1 IP addressing
192.168.1.0
1.
192.168.1.1
2. 192.168.1.2
3. 192.168.1.3
4. 192.168.1.4
1.
2.
3.
4.
192.168.2.0
192.168.2.1
192.168.2.2
192.168.2.3
192.168.2.4
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 23
9.2.1 IP addressing
A device is not said to have an address, but that
each of the connection points, or interfaces, on
that device has an address to a network.
2 NIC cards…
•2 MAC addresses
•2 IP addresses
192.168.1.0
1.
192.168.1.1
2. 192.168.1.2
3. 192.168.1.3
4. 192.168.1.4
Does not pass data
unless programmed
to do so.
1.
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4.
192.168.2.0
192.168.2.1
192.168.2.2
192.168.2.3
192.168.2.4
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 24
9.2.1 IP addressing
These are consecutive numbers.
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9.2.3 IPv4 addressing
192.168.0.0
192.168.1.0
192.168.2.0
192.168.3.0
192.168.4.0
192.168.5.0
192.168.6.0
192.168.7.0
192.168.8.0
192.168.9.0
192.168.10.0
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 26
9.2.3 IPv4 addressing
The only time that the host numbers matter is
when the data is on the local area network.
192.168.1.0
1.
192.168.1.1
2. 192.168.1.2
3. 192.168.1.3
4. 192.168.1.4
1.
2.
3.
4.
192.168.2.0
192.168.2.1
192.168.2.2
192.168.2.3
192.168.2.4
This number must be a unique number,
because duplicate addresses would
make routing impossible.
192.168.1.
192.168.1.
192.168.1.
192.168.2.
192.168.3.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 27
9.2.3 IPv4 addressing
Classful Addressing.
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A multicast address is a unique network address that directs packets with that destination address to
predefined groups of IP addresses.
Therefore, a single station can simultaneously transmit a single stream of data to multiple recipients.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 28
9.2.3 IPv4 addressing
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9.2.3 IPv4 addressing
All of these criteria identify the class of address.
The first octet range for Class E addresses is 11110000 to 11111111, or 240 to 255
Reserved for research by IETF
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 30
9.2.4 Class A, B, C, D, and E IP addresses
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9.2.4 Class A, B, C, D, and E IP addresses
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You can use these addresses on any private LAN.
You CANNOT use them on the internet.
Internet routers will block them.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 32
9.2.4 Class A, B, C, D, and E IP addresses
Error ?
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9.2.4 Class A, B, C, D, and E IP addresses
Error ?
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9.2.5 Reserved IP addresses
An IP address that has binary 0s in all host bit
positions is reserved for the network address.
A router uses the network IP address when it forwards data on
the Internet.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 35
9.2.5 Reserved IP addresses
An IP address that has binary 1s in all host bit
positions is reserved for the broadcast address.
Data that is sent to the broadcast address will be read by all hosts
on that network
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 36
9.2.5 Reserved IP addresses
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9.2.5 Reserved IP addresses
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9.2.5 Reserved IP addresses
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9.2.5 Reserved IP addresses
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9.2.6 Public and private IP addresses
It is appropriate to use
private addressing on the
private side of routers.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 41
9.2.6 Public and private IP addresses
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Originally, an organization known as the Internet Network
Information Center (InterNIC) handled IP assignments.
InterNIC no longer exists and has been succeeded by the
Internet Assigned Numbers Authority (IANA).
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 42
9.2.6 Public and private IP addresses
•Connecting a network using private addresses to the Internet requires
translation of the private addresses to public addresses.
•This translation process is referred to as Network Address Translation (NAT).
NAT is one solution to expand the number of public IP addresses. Two others are:
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classless interdomain routing
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IPv6
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 43
9.2.7 Introduction to subnetting
For communication to occur between different physical network segments:
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IP address of the local (RARP) and destination hosts must be obtained.
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Only then, is it possible to transfer data packets from one network
segment to another to reach the destination host.
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9.2.7 Introduction to subnetting
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9.2.7 Introduction to subnetting
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9.2.8 IPv4 versus IPv6
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9.2.7 Introduction to subnetting
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9.2.8 IPv4 versus IPv6
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Module Overview
9.1 Introduction to TCP/IP
9.1.1 History and future of TCP/IP
9.1.2 Application layer
9.1.3 Transport layer
9.1.4 Internet layer
9.1.5 Network access layer
9.1.6 Comparing the OSI model and the TCP/IP model
9.1.7 Internet architecture
9.2 Internet Addresses
9.2.1 IP addressing
9.2.2 Decimal and binary conversion
9.2.3 IPv4 addressing
9.2.4 Class A, B, C, D, and E IP addresses
9.2.5 Reserved IP addresses
9.2.6 Public and private IP addresses
9.2.7 Introduction to subnetting
9.2.8 IPv4 versus IPv6
9.3 Obtaining an IP Address
9.3.1 Obtaining an Internet address
9.3.2 Static assignment of an IP address
9.3.3 RARP IP address assignment
9.3.4 BOOTP IP address assignment
9.3.5 DHCP IP address management
9.3.6 Problems in address resolution
9.3.7 Address Resolution Protocol (ARP)
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 50
9.3.1 Obtaining an Internet address
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A network host needs a globally unique address in order to function on the Internet.
The physical or MAC address that a host has is only locally significant, identifying the host
within the local area network.
Since this is a Layer 2 address, the router does not use it to forward outside the LAN.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 51
9.3.1 Obtaining an Internet address
The Packet is removed from the Frame inside the NIC card.
Usually a
router.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 52
9.3.2 Static assignment of an IP address
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9.3.2 Static assignment of an IP address
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9.3.7 Address Resolution Protocol (ARP)
The RAM ARP table or
cache contains the IP and
MAC address of other
devices on the same LAN.
For any sending device to
communicate with another local
IP host, must have BOTH the IP
address and MAC (ARP) address
of the destination device.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 55
9.3.1 Obtaining an Internet address
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IP protocol is a hierarchical addressing scheme that allows individual
addresses to be associated together and treated as groups.
These groups of addresses allow efficient transfer of data across the
Internet.
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9.3.3 RARP IP address assignment
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9.3.1 Obtaining an Internet address
The Ethernet Type/Length field has the value 0x0806 to indicate an ARP
1.
2.
3.
4.
5.
6.
7.
8.
9.
Hardware Type - this is 1 for Ethernet.
Protocol Type - the protocol used at the network layer.
Hardware Address Length - this is the length in bytes, so it would be 6
for Ethernet (MAC).
Protocol Address Length - For TCP/IP the value is 4 bytes.
Operation Code - ARP Request (1), ARP Response (2), RARP Request (3)
RARP Response (4).
Senders Hardware Address - hardware address of the source node.
Senders Protocol Address - layer 3 address of the source node.
Target Hardware Address - used in a RARP request, the response
carries both the destination's hardware and layer 3 addresses.
Target Protocol Address - used in an ARP request, the response carries
both the destination's hardware and layer 3 addresses.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 58
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 59
1
0x806 6
4
1
00:e0:18:f4:95:9d
192.168.1.100
00:00:00:00:00:00
192.168.1.102
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 60
11
0x806 6
4
2
00:06:5b:1c:35:44
192.168.1.102
00:e0:18:f4:95:9d
192.168.1.100
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 61
ARP Request
1
1
0x806 6
4
1
00:e0:18:f4:95:9d
192.168.1.100
00:00:00:00:00:00
192.168.1.102
0x806 6
4
2
00:06:5b:1c:35:44
192.168.1.102
00:e0:18:f4:95:9d
192.168.1.100
ARP Response
The Op Code tells what kind of transaction it is. The missing information is shown as all 0’s
RARP Request
1
0x8035 6
4
3
00:06:5b:1c:35:44
1
0x8035 6
4
4
00:e0:18:f4:95:9d
0.0.0.0
192.168.1.100
00:e0:18:f4:95:9d
192.168.1.100
00:06:5b:1c:35:44
192.168.1.102
RARP Response
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 62
9.3.3 RARP IP address assignment
RARP binds a known MAC address to an IP unknown address.
1
0x8035 6
4
1
00:e0:18:f4:95:9d
192.168.1.100
00:00:00:00:00:00
192.168.1.102
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 63
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9.3.3 RARP IP address assignment
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9.3.3 RARP IP address assignment
BOOTP requires the administrator to set up a static IP
and MAC address table in the BOOTP server.
DHCP uses the same message structure.
Not used in
BOOTP
Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 66
9.3.3 RARP IP address assignment
Op
Htype
Operation: 1 = Request, 2 = Reply
H/w type: 1 = Ethernet
Not used in
BOOTP
Hlen
H/w Address Length
Hops
Initialized to zero. Incremented by BOOTP relays (routers)
Xid
Secs
Flags*
Ciaddr
Yiaddr
Siaddr
Giaddr
Chaddr
Server host
name
Boot File
name
Vendor
specific area
Transaction ID: used to match responses with requests
Seconds = Number of seconds since the client started to boot
BOOTP: not used *DHCP: Flags
If a client knows its IP address, it places it in the Client IP address. If
server address/name fields are non-zero in the request, only the
indicated host can answer the request
Your IP Address: Clients IP address returned by the server
IP address of the next server to use in bootstrap.
Relay agent IP address used in booting from a relay agent.
Client Hardware Address
Specifies particular server to get BOOTP information from
Generic name like "unix" in the request. Full name in response. Allows for
multiple boot files to be used allowing hosts to run different operating
systems.
Vendor specific information that can be passed to the host. Also used for
general purpose info.
Usually a
router
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9.3.4 BOOTP IP address assignment
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9.3.4 BOOTP IP address assignment
Only one bit of 16-bit Flags has been defined
•
Left-most flag bit =1 ? Servers, please reply using IP broadcast address
•
Servers by default send hardware unicast response
Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 69
The major advantages of DHCP over BOOTP are:
1.
It allows user to be mobile.
2.
It does not require fixed profiles to assign IP addresses.
Servers with a dynamically assigned IP address would be difficult to
locate on a network. Therefore they should have IP addresses assigned
statically by a network system administrator.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 70
Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 71
Op
Htype
Hlen
Hops
Xid
Secs
Ciaddr
Yiaddr
Siaddr
Giaddr
Chaddr
Server host
name
Boot File
name
Vendor
specific area
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Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 75
Vendor specific area:
•
Magic cookie: First 4 octets =
99.130.83.99
•
Type-length-value: describes the
option
•
•
•
Vendor specific field renamed to options
Size increased to 312 bytes (from 64 bytes)
Option type 53 specifies the "type of the
message"
Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor
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Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 79
Op Htype Hlen Hops Xid Secs Flags Ciadd Yiadd Siadd Giadd Chaddr Server Host Boot File Vendor
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 80
Once DHCP is finished, some operating systems send out an
ARP to prevent duplicate IP addresses on a local area network.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 81
9.3.6 Problems in address resolution
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•
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A datagram on a local-area network must contain both a destination MAC address and IP address.
These addresses must match the destination MAC and IP addresses of the host device.
If it does not match, the datagram will be discarded by the destination host.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 82
9.3.6 Problems in address resolution
Proxy ARP
“For any messages outside your
LAN, use my MAC address.”
•
•
•
Communications between two LAN segments have an additional task.
IP and MAC addresses are needed for both the destination host AND the intermediate routing
device.
TCP/IP has a variation on ARP called Proxy ARP that will provide the MAC address of an intermediate
device for transmission outside the LAN to another network segment.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 83
9.3.7 Address Resolution Protocol (ARP)
Each device on a network
maintains its own ARP table. When
a network device wants to send
data across the network, it uses
information provided by the ARP
table.
The MAC address for this “outside network” is
the Router interface MAC
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 84
9.3.7 Address Resolution Protocol (ARP)
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•
•
•
The default gateway is a HOST option where the IP address of the router interface is stored in the
network configuration of the host.
The HOST compares IP addresses to determine if the destination is located on the same segment.
If it is not, the host sends the data using the destination IP address router’s MAC address.
It learned the router’s MAC address from the ARP table by looking up the GATEWAY IP.
Nov-03 ©Cisco Systems CCNA Semester 1 Version 3 Comp11 Mod9 – St. Lawrence College – Cornwall Campus, ON, Canada – Clark slide 85
9.3.7 Address Resolution Protocol (ARP)
•
•
If the default gateway on the host OR the proxy ARP feature on the router is NOT
configured, no traffic can leave the local area network.
One or the other is required to have a connection outside of the local area network.
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Summary
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FIN
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