Transcript Welcome to ENTC 415 - Texas A&M University

Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Local Area & IP Networking
Review of Week #1
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Course Overview
LAN
WAN
425
9/2000
Network Fundamentals (w1)
Medium Access Control (w2-3)
Local Area Networking (w4)
Routing Protocols (w5)
Transport Protocols (w6)
Examples/Review (w7) TEST 1
IP Networking Support Protocols (w8)
IP Design (w9-10)
Group Presentations
Application Support Protocols (w11-12)
Network Security (w13)
Makeup Week (w14)
TEST 2
Final Project Due last week of class
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Required Reading
Computer Communications & Networking
Technologies
pp. 229-274
RFC 1180
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“A TCP/IP Tutorial”
Sections 1-5
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Lecture Outline
IEEE Standard LAN:
IEEE Standard LAN vs. OSI Model
• LLC
• MAC
Ethernet – 802.3
• Overview
• Frame Format
Other LAN Protocols:
FDDI – ANSI X.3 (X3T9.5)
• Operation
• Frame format
MAC Addressing
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Lecture Outline
IP Addressing:
The IP Address
Subnetting (Classful, VLSM, CIDR)
Supernetting (CIDR)
Private vs. Public Addresses
• Address Resolution Protocol:
ARP
Binding
RARP
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing
The IP Address
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing Scheme
A host is assigned a unique address for each network connection.
The IP address is divided into a network ID and host ID. The
host ID indicates the host’s connection to the network.
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing Scheme (Cont..)
 The IP address is represented by 32 bits. It is often
convenient to represent the address in decimal-dot notation
as shown below:
Decimal-dot : 111.23.129.8
Binary: 1101111.0010111.10000001.00001000
 The Min value of an Octet (8bits) is 0, Max is 255
 Network Ids assigned globally, host Ids assigned locally
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Dotted Decimal Notation
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing
Three Primary Classes
 Class A : N.H.H.H
 Class B : N.N.H.H
 Class C : N.N.N.H
N = Network number assigned globally
H = Assigned by network administrator (host & subnets)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Internet Classes
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Class
Range of Vaules
A
B
C
D
E
0 through 126
128 through 191
192 through 223
224 through 239
240 through 255
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Internet Classes (Cont..)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Internet Classes (Cont..)
 Class A, B and C are primary classes
 Class D is used for multicast
- Internet hosts join a multicast group
- Packets are delivered to all members of group
- Routers manage delivery of single packet from source to
all members of multicast group
- Used for mbone (multicast backbone)
 Class E is reserved
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Computing The Class Of An Address
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First four bits
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
Index
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Class
A
A
A
A
A
A
A
A
B
B
B
B
C
C
D
E
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Class Ranges Of Internet Addresses
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing - Class A (example)
 1.222.222.222
 Network # : 1
 Host # : 222.222.222
 Range of network numbers is : 1-126 (0 and 127 reserved)
 Maximum number of class A networks : 126
 Number of available hosts : 16,777,214 (all 0’s and all 1’s
reserved)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing - Class B (example)
 128.128.222.222
 Network # : 128.128
 Host # : 222.222
 Range of network numbers is : 128 - 191
 Maximum number of networks : 16384
 Number of available hosts : 65,534
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing - Class C (example)
 192.192.192.222
 Network # : 192.192.192
 Host # : 222
 Range :192- 223
 Maximum number of networks : 2097152
 Number of available hosts : 264 per network
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP First Octet Rule
 1 - 126 :
 128 - 191 :
 192 - 223 :
 224 - 239 :
 240 - 254 :
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Class A
Class B
Class C
Class D
Class E
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Summary of Special IP Addresses
Prefix
Suffix
Type
Purpose
all 0s
network
network
all 1s
127
all 0s
all 0s
all 1s
all 1s
any
this computer
network
directed broadcast
limited broadcast
loopback
used during bootstrap
identifies a network
broadcasts on a specified net
broadcast on a local net
testing
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing Example
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Reference Information
IP Address
Class
Format
Purpose
HighOrder
Bit(s)
0
Address Range
A
N.H.H.H
Large
organizations
B
N.N.H.H
Medium
organizations
1,0
128.1.0.0 to
191.254.0.0
C
N.N.N.H
Small
organizations
1,1,0
D
N/A
Multicast
groups
E
N/A
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1.0.0.0 to
126.0.0.0
192.0.1.0
to
223.255.254.0
1,1,1,0
224.0.0.0 to
239.255.255.255
Experimental 1,1,1,1
240.0.0.0 to
254.255.255.255
# of Bits Max. Host
Network/
Host
7/24
16,777,2142
(224-2)
14/16
65,534 (2162)
22/8
254 (28-2)
N/A
N/A
N/A
N/A
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
PART 1
CLASSFUL & SUBNET MASKING
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
CLASSFUL & SUBNET MASKING
• Original classful addressing
– Did not anticipate Internet growth
– Originally allocated based on organization, not need
• Classful A, B, and C addressing
– A concept that is easy to understand
– Still wasteful
• Classic natural mask addresses
– Difficult to manage devices on each network
– A Class B address, for example, must manage large
numbers of devices
• Subnetting
– Simplified the address management process
– Better address optimization
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
THE CONCEPT OF MASKING
A Class B address:
NetID
HostID
184
.
10
.
0
.
0
1011 1000 . 0000 1010 . 0000 0000 . 0000 0000
The Mask:
1111 1111 . 1111 1111 . 0000 0000 . 0000 0000
255
.
255
.
0
.
0
Or:
184
.
10
.
0
.
0 / 16
In other words, we can write this as:
184.10.0.0/16
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
CLASSFUL ADDRESSES
A Class A classful address:
28.0.0.0/8
0001 1100 . 0000 0000 . 0000 0000 . 0000 0000
A Class B classful address:
183.248.0.0/16
1011 0111 . 1111 0000 . 0000 0000 . 0000 0000
A Class C classful address:
208.136.58.0/24
1101 0000 . 1000 1000 . 0011 1010 . 0000 0000
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
JUST A NOTE
The Class A address:
127.0.0.0
Also written:
127/8
Or:
127.0.0.0/8
Has been reserved for “Loopback” interface where a client
and server are allowed to communicate with one another
when they are located on the same host.
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
HOW MANY NETWORKS/HOSTS ARE
ALLOWED?
•
Class B address ID allows for 214 - 2 networks, or 16,382
– Because first 2-bits define a Class B address, and
– All Os (set aside for an initialization process) and all 1s (set aside for
broadcast)
•
Class B host ID allows for 216 - 2 hosts, or 65,534
– Because all 0s are set aside for meaning “this network” and
– All 1s are set aside for broadcasting to all hosts on this network
•
This applies to Class A and Class C addresses as well
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
SUBNETTING CLASSFUL ADDRESSES
•
•
•
You are given a Class B address 141.6.0.0/16
This will give you 216 - 2 hosts or 65,534 devices on this network
Subnetting this classful address potentially makes this more manageable
NOTE: Subnetting steals from the HOSTs to give to the Network ID
141 .
6 .
0
.
0
/ 16
1000 1101 . 0000 0110 . 0000 0000 . 0000 0000
141 .
6 .
0
.
0
1000 1101 . 0000 0110 . 0000 0000 . 0000 0000
141 .
6 .
0
.
0
/ 18
4 subnets & 16,382 hosts
/ 24
256 subnets & 254 hosts
1000 1101 . 0000 0110 . 0000 0000 . 0000 0000
141 .
6 .
0
.
0
1000 1101 . 0000 0110 . 0000 0000 . 0000 0000
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4096 subnets & 14 hosts
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
SUBNETTING CLASSFUL ADDRESSES
•
Let us focus on the classful address 141.6.0.0/28
141 .
6 .
0
.
0
/ 28
1000 1101 . 0000 0110 . 0000 0000 . 0000 0000
•
212 = 4096 subnets are possible but
– All 0s and all 1s are potentially not allowed - RFC 950
– Function of the Interior Gateway Protocol (IGP) in use
– Today, all 0 and all 1subnet addresses ARE available
•
24 = 16 hosts are possible, but
– All 0s and all 1s are still not allowed
– Or 24 - 2 = 30 hosts on each subnetwork
•
Therefore
– 4096 subnests and
– 30 hosts on each subnet
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
AN EXAMPLE
•
You are given the Class C address of
198 .
6 .
1
.
0 / 29
1100 0000 . 0000 0110 . 0000 0001 . 0000 0000
•
32 subnets & 6 hosts
Defining Subnet Numbers
Subnet O (000002)
Subnet 1 (000012)
•
•
•
Subnet 30 (111102)
Subnet 31 (111112)
•
Thus, the address of Host 5 on Subnet 30 is 188.6.1.21 or
1100 0000 . 0000 0110 . 0000 0001 . 1111 0101
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
A 2nd EXAMPLE OF MASKING USING
LOGICAL ‘AND’
•
You are given the Class C address and mask of
198 .
6 .
1
.
0
255 . 255 . 255 . 236
1100 0110 . 0000 0110 . 0000 0001 . 0000 0000
32 subnets & 6 hosts
1111 1111 . 1111 1111 . 1111 1111 . 1110 1100
•
Defining Subnet and Host Numbers
Subnet O (000x00xx2)
Host O (xxx0xx012)
Subnet 1 (000x01xx2)
Host 1 (xxx0xx102)
Subnet 30 (111x10xx2)
Host 4 (xxx1xx012)
Subnet 31 (111x11xx2)
Host 5 (xxx1xx102)
•
•
•
•
•
•
•
Thus, the address of Subnet 30 & Host 5 is 188.6.1.250 or
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1100 0110 . 0000 0110 . 0000 0001 . 1111 1010
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
TERMINOLOGIES
•
You are given the Class B address of
130 .
101 .
0
.
0 / 24
1000 0010 . 0110 0101 . 0000 0000 . 0000 0000
•
Masking terms
– Natural mask also called the network-prefix
1000 0010 . 0110 0101 . 0000 0000 . 0000 0000
– Subnet mask
1000 0010 . 0110 0101 . 0000 0000 . 0000 0000
– Extended-network-prefix = natural plus subnet masks
1000 0010 . 0110 0101 . 0000 0000 . 0000 0000
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
PART 2
VARIABLE LENGTH SUBNET MASKS
(VLSMs)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VARIABLE LENGTH SUBNET MASK (VLSM)
•
•
•
With subnet masking, one network, one mask
With VLSM, one network can be configured with different masks
Example: You are assigned a Class C address of 196.4.1.0/24. You
need to divide that network into 3 subnets
– Example: You are assigned a Class C address of 190.4.1.0/24. You need
to divide that network into 3 subnets
– Subnet 1 needs to host 100 devices
– Subnet 2 needs to host 50 devices, and
– Subnet 3 needs to host 50 devices.
– Subnet masking choices given X :
196.4.1.0/24
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255.255.255.X
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM EXAMPLE
– Subnet masking choices given X :
196.4.1.0/24
255.255.255.X
X = 252 (1111 1100) - 64 subnets with 2 hosts each
X = 248 (1111 1000) - 32 subnets with 6 hosts each
X = 240 (1111 0000) - 16 subnets with 14 hosts each
X = 224 (1110 0000) - 8 subnets with 30 hosts each
X = 192 (1100 0000) - 4 subnets with 62 hosts each
X = 128 (1000 0000) - 2 subnets with 126 hosts each
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM EXAMPLE - CONT’D
– Subnet masking choices given X :
196.4.1.0/24
255.255.255.X
X = 192 (1100 0000) - 4 subnets with 62 hosts each
X = 128 (1000 0000) - 2 subnets with 126 hosts each
Subnet 1 - 126 hosts
Subnet 1 - 62 hosts
Subnet 2 - 62 hosts
Subnet 3 - 62 hosts
Subnet 2 - 126 hosts
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Subnet 4 - 62 hosts
Router
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM EXAMPLE - CONT’D
•
The VLSM solution :
196.4.1.0/24
E0 1100 0100 . 0000 0100 . 0000 0001 . xxxx xxxx
E1
E2
E3
E4
E1 126 hosts
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E3 126 hosts
196.4.1.0/25
1100 0100 . 0000 0100 . 0000 0001 . 0xxx xxxx
196.4.1.0/25
1100 0100 . 0000 0100 . 0000 0001 . 1xxx xxxx
196.4.1.0/26
1100 0100 . 0000 0100 . 0000 0001 . 10xx xxxx
196.4.1.0/26
1100 0100 . 0000 0100 . 0000 0001 . 11xx xxxx
E1 126 hosts
E3 62 hosts
E4 62 hosts
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM EXAMPLE - CONT’D
•
More splitting :
E0
E1
E2
E3
E4
E5
E1 126 hosts
E0
254 hosts
E59/2000
30 hosts
E6
196.4.1.0/24
1100 0100 . 0000 0100 . 0000 0001 . xxxx xxxx
196.4.1.0/25
1100 0100 . 0000 0100 . 0000 0001 . 0xxx xxxx
196.4.1.0/25
1100 0100 . 0000 0100 . 0000 0001 . 1xxx xxxx
196.4.1.0/26
1100 0100 . 0000 0100 . 0000 0001 . 10xx xxxx
196.4.1.0/26
1100 0100 . 0000 0100 . 0000 0001 . 11xx xxxx
196.4.1.0/27
1100 0100 . 0000 0100 . 0000 0001 . 110x xxxx
196.4.1.0/27
1100 0100 . 0000 0100 . 0000 0001 . 111x xxxx
E3 62 hosts
E6 30 hosts
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
ANOTHER VIEW OF VLSM
VLSM Cascaded Routers
E1
126 hosts
E0
254 hosts
E3
62 hosts
E2
126 hosts
E5
30 hosts
E4
62 hosts
Single VLSM Router
E6
30 hosts
E1 126 hosts
E0
254 hosts
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E5 30 hosts
E3 62 hosts
E6 30 hosts
Ethernet Hub
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
AGGRIGATION & ADVERTIZMENTS
A real advantage. Here’s why:
Two-Level Classful Hierarchy
Network-Prefix
Host-Number
Three-Level Classful Hierarchy
Network-Prefix
IP
Network
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E0 141.6.0.0/ 24
Subnet
Number
Host
Number
E1
E2
E3
E4
E5
E6
E7
141.6.32.0
141.6.64.0
141.6.96.0
141.6.128.0
141.6.160.0
141.6.192.0
141.6.224.0
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM PERMITS ROUTE TABLE
AGGRIGATION & ADVERTIZEMENT
Autonomous Network
11.1.0.0/16
11.0.0.0/8
or 11/8
A
11.1.0.0/16
11.2.0.0/16
11.3.0.0/16
•
•
11.252.0.0/16
11.253.0.0/16
11.254.0.0/16
B
11.1.1.0/24
11.1.2.0/24
•
•
•
11.1.253.0/24
11.1.254.0/24
IP
Network
11.253.0.0/19
NOTE: It may help to
write these numbers
in dot binary and use
a marker to define the
appropriate mask
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C
11.253.32.0/19
11.253.64.0/19
•
•
11.253.160.0/19
11.253.192.0/19
11.1.253.0/27
D
11.1.253.32/27
11.1.253.64/27
•
•
11.1.253.160/27
11.1.253.192/27
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
VLSM PERMITS ROUTE TABLE
AGGRIGATION & ADVERTIZEMENT (con’d)
Autonomous Network
11.1.0.0/16
27
000 1011.0000 0001.1111 1101.0010 0000 32
000 1011.0000 0001.1111 1101.0100 0000 64
000 1011.0000 0001.1111 1101.0110 0000 96
000 1011.0000 0001.1111 1101.1000 0000 128
000 1011.0000 0001.1111 1101.1010 0000 160
000 1011.0000 0001.1111 1101.1100 0000 192
19
000 1011.1111 1101. 0010 0000 32
000 1011.1111 1101. 0100 0000 64
000 1011.1111 1101. 0110 0000 96
000 1011.1111 1101. 1000 0000 128
000 1011.1111 1101. 1010 0000 160
000 1011.1111 1101. 1100 0000 192
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11.1.0.0/16
11.2.0.0/16
11.3.0.0/16
•
•
11.252.0.0/16
11.253.0.0/16
11.254.0.0/16
11.253.0.0/19
C
11.253.32.0/19
11.253.64.0/19
•
•
11.253.160.0/19
11.253.192.0/19
B
11.1.1.0/24
11.1.2.0/24
•
•
•
11.1.253.0/24
11.1.254.0/24
11.1.253.0/27
D
11.1.253.32/27
11.1.253.64/27
•
•
11.1.253.160/27
11.1.253.192/27
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
SUMMING UP SUBNETS & VLSM SO FAR
• Classic natural mask addresses
– Difficult to use
– Very address wasteful
• Subnetting
– Simplified the address management process
– Better address optimization
• VLSM
–
–
–
–
9/2000
Also simplifies address management
Also improves address optimization over subnetworking
Simplifies routing tables
Simplifies address advertising
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
SUMMING UP SUBNETS & VLSM SO FAR
• Not all routing protocols can handle VLSM. Early
network protocols did not
– Routing Information Protocol (RIP) Version 1
– Interior Gateway Routing Protocol (IGRP) which is Cisco
proprietary
• Today’s routing protocols do support VLSM
– Open Shortest Path First (OSPF)
– Enhanced Internet Gateway Protocol (EIGRP), a Cisco
proprietary protocol
– Intermediate System-to-Intermediate System (IS-IS)
– RIP Version 2
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Private vs. Public Addresses
• Some IP Addresses have been reserved for private
use meaning that they cannot be routed over the
Internet. Specifically, the following networks are
reserved for private use.
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Private IP Addresses
Private addresses can only be used for internal
networks. RFC 1918 spells out a set of addresses
which are prohibited from being used on the
Internet.
Network Address
Available Allocation
10.0.0.0
1 Class A network
172.16.0.0 through 172.31.0.0
16 Class B networks
192.168.255.0 through 192.168.255.0 255 Class C networks
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
ARP - Binding
The interface between IP Addresses and MAC Addresses
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
What Is Binding ?
Association between a protocol address and a
hardware(MAC) address is called a binding
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
What Is Address Resolution ?
Translation from a computer’s protocol
address to an equivalent hardware address
or
Mapping between a protocol address and a
hardware address
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Why Address Resolution ?
Upper levels of protocol stack use protocol addresses
(example = IP addresses)
Network hardware must use hardware address for
eventual delivery (example = MAC addresses)
Protocol address must be translated into hardware address
for delivery (LAN Equipment, at layer 2, will bind MAC
addresses to IP Addresses)
Translation occurs in data link layer
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
A computer never resolves the
MAC address of a computer
attached to a remote network
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Address Resolution
How can Node A resolve the MAC address of Node B?
How can it resolve the MAC address of Node F?
How can it resolve the MAC address of Router R1?
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Address Resolution
Techniques
Three techniques :
Table lookup
Closed-form computation
Message exchange (dynamic)
TCP/IP can use any of the three methods
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Table Lookup
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IP Address
Hardware Address
197.15.3.2
197.15.3.3
197.15.3.4
197.15.3.5
197.15.3.6
197.15.3.7
0A:07:4B:12:82:36
0A:9C:28:71:32:8D
0A:11:C3:68:01:99
0A:74:59:32:CC:1F
0A:04:BC:00:03:28
0A:77:81:0E:52:FA
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Table Lookup (Cont.......)
197.15.3 .5
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A0:14:52:44:F2:91
0A:07:4B:12:82:36
0A:9C:28:71:32:8D
0A:11:C3:68:01:99
0A:74:59:32:CC:1F
0A:04:BC:00:03:28
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Closed-form Computation
Network administrator can choose hardware address
based on IP address
Example - hardware uses one octet address that can be
configured
Simply choose hardware address to be hostid
 hardware_address = ip_address & 0xff
THIS IS TECHNIQUE IS NOT ADVISED!!!!!
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Message Exchange
(Dynamic Resolution)
Message exchange
Server based
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Distributed
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Message Exchange
(Dynamic Resolution) (Cont.)
Use network to resolve IP addresses
Message exchange with other computer(s) returns
 hardware address to source
Server based :- computer sends message to server to
resolve address
Distributed (ARP):- all computers participate; destination
provides hardware address to host
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Distributed Dynamic Resolution
Or Address Resolution Protocol
(ARP)
TCP/IP uses distributed resolution technique
Address Resolution Protocol (ARP) - part of TCP/IP
protocol suite
Two-part protocol
Request from source asking for hardware address
Reply from destination carrying hardware address
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Distributed Dynamic Resolution
Or Address Resolution Protocol
(ARP)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Distributed Dynamic Resolution
Or Address Resolution protocol
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
ARP Message Format
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
ARP Message Format
(Cont........)
HARDWARE ADDRESS TYPES= 1 for Ethernet
PROTOCOL ADDRESS TYPES = 0x0800 for IP
HADDR LEN & PADDR LEN (number of octets in
hardware & protocol address)
OPERATION = 1 (for request);
= 2 (for response)
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Reverse ARP (RARP)
What is the IP address of a given hardware address ?
Hardware to IP address resolution
Used by diskless systems to find their own IP address
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
RARP Illustrated
Here’s my MAC
address. What is my
IP address ?
0800.0020.1111
I know who you are,
here’s your IP
address
131.108.3.2
Ethernet : 0800.0020.1111
IP = ????
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IP = 131.108.3.1
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
IP Addressing Protocols
RARP
BOOTP
ICMP
DHCP
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Bootstrapping
• Computer loads a simple boot program. The boot program
loads operating system
• When is protocol software loaded during booting?
• Protocol software may be:
- Run out of on-board PROM
- Loaded with bootstrap program from disk
- Loaded with operating system from disk
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Diskless Machines
• Uses network as part of the bootstrap process
• The computer needs to know the network address of the
o/s file
• It needs to know its own IP address
• It only knows its h/w address
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Configuration
• Protocols are software routines
• Protocol software employs parameters for operation on a
specific hardware and network
• Different nodes have different parameters
“Configuration = setting the parameters”
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Example Parameters
• IP address - depends on network, must be unique on
network
• Default router address - where to send packets aimed at
remote network
• Subnet mask - to specify if subnet addressing is used and
what the subnet is
• DNS server address - for DNS queries
• Server addresses
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Methods Of Protocol
Configuration
Methods
Manual
Local disk file
Automated through network
RARP
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ICMP
BOOTP
DHCP
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Automated Protocol
Configuration
• How can host use network to get network address?
• Use broadcast-based link-layer protocol
- RARP
- AppleTalk, etc.
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
RARP
• Reverse ARP (remember): “What is the IP address of
hardware address xx:xx:…..?”
• Host broadcasts RARP request with its MAC address
• But RARP uses IP => Needs IP address
• Solution: Use 00.00.00.00 as source address
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
ICMP
•
•
•
•
ICMP address mask request - find subnet mask
ICMP gateway discovery - find default router
Host broadcasts ICMP queries
Problem: What is the bootfile name for IP address
nn.nn.nn…?
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
Sequence Of Protocols Used During
Bootstrap
1.
2.
3.
4.
Broadcast RARP request
Extract IP address from RARP response
Broadcast ICMP address mask request
Extract subnet mask from ICMP address mask
reply
5. Broadcast ICMP gateway discovery request
6. Extract default router from ICMP gateway
discovery reply
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
BOOTP
• Allows remote booting from a server on the same network
or different physical network
• Broadcast BOOTP (Bootstrap protocol) request
• Reply: IP address, Boot Server IP address, Default router,
Bootfile name, subnet mask
• Host gets boot image using a simple FTP program
- Trivial File Transfer Protocol (TFTP)
• Problem: Why waste an address when it is not being used
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
BOOTP Message Format
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
DHCP
Dynamic Host Configuration Protocol (DHCP), was
devised by the IETF to automate configuration of
terminal IP addresses.
– DHCP provides a mechanism that allows a computer to
join a new network an d obtain an IP address without
manual intervention.
– Terminals use client software to send a DHCP Request
when booted.
– A terminal running DHCP software will send a DHCP
Reply containing an IP address and a default gateway to
the terminal.
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Telecommunication Engineering Technology, Texas A&M University LAN WAN Lecture Notes - Copyright Jeff M. McDougall 2001
DHCP
IP addresses are leased for a finite period of time.
When a lease ends, the terminal must request
another IP address or an extension to the lease.
– Terminals must discover if a DHCP server exists
through a DHCP Discover message. The terminal will
cach the server location for future use.
– DHCP message carry no information about DNS
servers!
What happens to servers using DHCP that have entries in
a DNS database?
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