Download Figure 8-2

TCP/IP Internetworking
Chapter 8
Panko’s
Business Data Networks and Telecommunications, 6th edition
Copyright 2007 Prentice-Hall
May only be used by adopters of the book
Recap
• Single Networks (Subnets)
– Chapters 4 and 5 covered single LANs
– Chapters 6 and 7 covered residential Internet access
and single WANs
• Internets
– Connect multiple single networks using routers
– 70%-80% of internet traffic follows TCP/IP standards
– These standards are created by the IETF
– Chapter 10 looks in more detail at TCP/IP
management
8-2
Figure 2-8: Hybrid TCP/IP-OSI Architecture
Recap
Specific Purpose
General Purpose
Layer
Application-application
communication
Application (5)
Application-application
interworking
Transmission across an
internet
Transport (4)
Host-host
communication
Internet (3)
Packet delivery across
an internet
Data Link (2)
Frame delivery across a
network
Transmission across a
single network (LAN or
WAN)
Physical (1)
Device-device
connection
TCP/IP standards dominate at the
internet and transport layers—
transmission across an internet
8-3
Figure 2-11: Internet and Transport Layer, Cont.
Recap
Client PC
Transport Layer
end-to-end (host-to-host)
TCP is connection-oriented, reliable
UDP is connectionless and unreliable
Server
Internet Layer
(usually IP)
hop-by-hop (host-router or router-router)
connectionless, unreliable
Router 1
Router 2
Router 3
8-4
Frames and Packets
Recap
• Messages at the data link layer are called frames
• Messages at the internet layer are called packets
• Within a single network, packets are encapsulated
in the data fields of frames
Frame
Trailer
Packet
(Data Field)
Frame
Header
8-5
Frames and Packets
Recap
• In an internet with hosts separated by N
networks, there will be:
– 2 hosts
– One packet (going all the way between hosts)
• One route (between the two hosts)
– N frames (one in each network)
• N-1 routers (change frames between each pair of
networks)
8-6
Figure 2-21: Combining Horizontal and Vertical
Communication
Recap
Horizontal Communication
App
Transmission Control Protocol (TCP)
Or User Datagram Protocol (UDP)
Trans
Int
Trans
Internet Protocol
(IP)
Int
IP
Router
1
Switch
3
Int
Int
DL
Phy
Source
Host
Switch
1
Switch
2
Router Destination
Host
2
8-7
Figure 8-1: Major TCP/IP Standards
User Applications
5 Application
HTTP
4 Transport
3 Internet
2 Data Link
SMTP
Many
Others
Supervisory Applications
DNS
TCP
IP
Routing Many
Protocols Others
UDP
ICMP
MPLS
ARP
None: Use OSI Standards
1 Physical
None: Use OSI Standards
Internetworking is done at the internet and transport layers.
There are only a few standards at these layers.
We will look at the shaded protocols in this chapter.
8-8
Figure 8-1: Major TCP/IP Standards, Continued
User Applications
5 Application
HTTP
4 Transport
3 Internet
2 Data Link
SMTP
Many
Others
TCP
Supervisory Applications
DNS
Routing Many
Protocols Others
UDP
IP
ICMP
ARP
None: Use OSI Standards
1 Physical
Use OSI
At the None:
application
layer,Standards
there are
user applications and supervisory applications.
We will look at two TCP/IP
application layer supervisory applications in this chapter.
8-9
Figure 8-2: IP, TCP, and UDP
Recap
Protocol Layer
Connection- Reliable /
Oriented/
Unreliable
CNLS
Lightweight /
Heavyweight
TCP
4. Trans
Connection- Reliable
oriented
Heavyweight
UDP
4. Trans
CNLS
Unreliable
Lightweight
IP
3. Int
CNLS
Unreliable
Lightweight
Note: CNLS = connectionless
8-10
IP Addresses
Figure Figure
8-3:8-3:Hierarchical
IP Address
Hierarchical IP Address
Network Part (not always 16 bits)
Subnet Part (not always 8 bits)
Host Part (not always 8 bits)
Total always is 32 bits
128.171.17.13
The Internet
UH Network (128.171)
IP addresses are not
simple 32-bit numbers.
They usually have 3 parts.
Consider the example
128.171.17.13
Host 13
CBA Subnet (17)
8-12
Hierarchical Addressing
• Hierarchical Addressing Brings Simplicity
– Phone System
• Country code-area code-exchange-subscriber
number
• 01-808-555-9889
– Long-distance switches near the top of the hierarchy
only have to deal with country codes and area codes to
set up circuits
– Similarly, core Internet routers only have to consider
network or network and subnet parts of packets
8-13
E
D
IPv4 Address Formats
0 ~ 127
C
A
B
128 ~ 191
192 ~ 223
224 ~ 239
240 ~
8-14
IP Addresses - Class A
• 32 bit global internet address
• Network part and host part
• Class A
– Start with binary 0
– All 0 reserved (0.0.0.0)
– 01111111 (127) reserved for loopback
– Range 1.x.x.x to 126.x.x.x
– All allocated
8-15
IP Addresses - Class B
• Start 10
• Range 128.x.x.x to 191.x.x.x
• Second Octet also included in network address
• 214 = 16,384 class B addresses
• All allocated
8-16
IP Addresses - Class C
• Start 110
• Range 192.x.x.x to 223.x.x.x
• Second and third octet also part of network
address
• 221 = 2,097,152 addresses
• Nearly all allocated
– See IPv6
8-17
Special IP Addresses
• All-0 host suffix Network Address
– 163.22.20.16/24  163.22.20.0/24
• All-1 host suffix All hosts on the destination net
(directed broadcast)
163.22.20.16/24  163.22.20.255
• All-0s This computer
– 0.0.0.0
• All-1s All hosts on this net (limited broadcast)
– 255.255.255.255
Subnet number cannot be all 1
• All-0s network This network.
– 163.22.20.7/24  0.0.0.7 (Host 7 on this network)
• 127.*.*.* Loopback through IP layer
– 127.0.0.1
8-18
Private IP Addresses
• Any organization can use these inside their network
• Can’t go on the internet. [RFC 1918]
– 10.0.0.0 - 10.255.255.255 (10/8 prefix)
1
– 172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
16
– 192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
256
• Network Address Translation (NAT)
– Basic NAT (one-to-one NAT)
– NAT(NAPT, Network Address Port Translation)
8-19
Router Operation
Figure 8-4: Border Router, Internet Router,
Networks, and Subnets
Figure 8-4: Border Router, Internal Router, Netw orks, and Subnets
Subnet 192.168.2.x
Internal
Router
Subnet 192.168.3.x
Subnet
192.168.1.x
Corporate
Network
192.168.x.x
Border
Router
ISP Network
60.x.x.x
Border routers connect different Internet networks
(In this case, 192.168.x.x and 60.x.x.x).
An “x” indicates anything.
8-21
Figure 8-4: Border Router, Internet Router,
Networks, and Subnets
Figure 8-4: Border Router, Internal Router, Netw orks, and Subnets
Subnet 192.168.2.x
Internal
Router
Subnet 192.168.3.x
Subnet
192.168.1.x
Corporate
Network
192.168.x.x
Border
Router
ISP Network
60.x.x.x
Internal routers connect different subnets in a network.
In this case, the three subnets are boxed in red:
192.168.1.x, 192.168.2.x, and 192.168.3.x.
8-22
Figure 8-5:
Multiprotocol Routing
Figure 8-5: Multiprotocol Routing
Site B
Site A
UNIX
Server
Ethernet
LAN 2
Ethernet
LAN 1
Edge Mainframe
IPX/
SNA
Old
Router
NetWare SPX
Z
Server TCP/
IP
Multiprotocol
Router
The Internet
TCP/
X
Ethernet
IP
Lan 3
Internal
Router
Real routers
must handle multiple
Y layer architectures—
internet and transport
WWW
Server
TCP/IP, IPX/SPX, SNA, etc.
We will only look at TCP/IP routing
8-23
Figure 8-6: Ethernet Switching Versus IP Routing
Ethernet Switching
Switch
2
5 on Switch
1
The switch readsPort
the frame’s
destination
address Port 7 on Switch 2
to Port 4 on Switch 3
to Port
3 on Switch 2
(In this case,
E5-BB-47-21-D3-56).
The switch locates the frame’s one matching row.
The switch sends the frame out the indicated port.
Switching Table Switch 1
(In this case, Port 5)
Ethernet switching is simple, fast, Port Station
and
therefore inexpensive
Switch
2
A1-44-D5-1F-AA-4C
1
A1-44-D5-1F-AA-4C
Switch 1, Port 2 B2-CD-13-5B-E4-65
Switch 1, Port 7
7
5
5
5
B2-CD-13-5B-E4-65
C3-2D-55-3B-A9-4F
D4-47-55-C4-B6-9F
E5-BB-47-21-D3-56
One Correct Row
8-24
Figure 8-6: Ethernet Switching Versus IP Routing
8-25
Figure 8-6: Ethernet Switching Versus IP Routing
Router
RoutingA
Interface
1
Router B
IP Routing
Packet to 60.3.47.129 Interface
2
Network
60.x.x.x
Routing Table for Router A
Matches
IP Address
Next-Hop
Route
Range Metric Router
Router C
Network
1
60.3.x.x
9
B
60.3.x.x
2 128.171.x.x 2
B
3
60.3.47.x
8
C
Host
4
10.5.3.x
6
B
60.3.45.129
of multiple
5Because
128.171.17.x
2 alternative
Local routes,
Routers may
have
several rows
thatCmatch an IP address.
6
10.4.3.x
2
Routers must find all matches and then select the best one.
This is slow and expensive compared to switching.
8-26
Figure 8-7: The Routing Process
• Routing
– Processing an individual packet and passing it on its way
is called routing
• Router ports are called interfaces
• Packet arrives in one interface
• The router sends the packet
out another interface
8-27
Figure 8-7: The Routing Process
• The Routing Table
C:\> route print
– Each router has a routing table that it uses to make
routing decisions
– Routing Table Rows
• Each row represents a route for a RANGE of IP
addresses—often a network or subnet
• All packets with addresses in this range are routed
according to that row
Route
IP Address Range
Governed by the route
Metric
Next-Hop
Router
1
60.3.x.x
9
B
8-28
Figure 8-7: The Routing Process
• The Routing Table
– Routing Table Columns
• Row (route) number: Not in real routing tables
• IP address range governed by the row
• Metric for the quality of the route
• Next-hop router that should get the packet next if the
row is selected as the best match
Route
IP Address
Range
Metric
Next-Hop
Router
1
2
60.3.x.x
128.171.x.x
9
2
B
B
8-29
Figure 8-7: The Routing Process
• A Routing Decision
– The router looks at the destination IP address in an
arriving packet (in this case, 60.3.47.12).
– 1. The router determines which rows match (have an IP
address range containing the packet’s destination IP
address)
• The router must check ALL rows for possible matches
Route
IP Address
Range
Metric
Next-Hop
Router
Arriving Packet
60.3.47.12
1
2
60.3.x.x
128.171.x.x
9
2
B
B
Match
No Match
8-30
Figure 8-7: The Routing Process
• A Routing Decision
– 2. After finding all matches, the router then determines
the best-match row
• 2A. Selects the row with the longest length of match
– 60.3.x.x has 16 bits of match
– 60.3.47.x has 24 bits of match so is a better match
• 2B. If two or more rows tie for the longest length of
match, router uses the metric column value
– If cost, lowest metric value is best
– If speed, highest metric value is best
– Etc.
8-31
Figure 8-7: The Routing Process
• A Routing Decision
– 3. After selecting the best-match row, the router sends
the packet on to the next-hop router indicated in the
best-match row—Next-Hop Router B in this example.
Route
IP Address
Range
Metric
Next-Hop
Router
1
2
60.3.x.x
128.171.x.x
9
2
B
B
Send Packet
out to
NHR B
Best-Match Row
8-32
Box
A More Detailed Look at
Routing Decisions
Figure 8-8: Detailed Row-Matching Algorithm
Box
• Routing Table
IP Address Range
Row
Destination
Mask
…
…
…
1
10.7.3.0
255.255.255.0
…
…
…
2
…
…
…
…
…
Actually, the table does not really have an “IP Address Range” column.
3 It has two…
… range:
…
…
columns to indicate…
the IP address
Destination (an IP address) and a mask
8-34
Figure 8-8: Detailed Row-Matching
Algorithm
Box
• 1. Basic Rule of Masking
– Information Bit
1 0 1 0
– Mask Bit
1 1 0 0
– Result
1 0 0 0
• Where mask bits are one, the result gives the
original IP address bits
• Where mask bits are zero, the result contains zeros
8-35
Figure 8-8: Detailed Row-Matching
Algorithm
Box
• 2. Example
– Address (partial)
10101010
11001110
– Mask
11111000
00000000
– Result
10101000
00000000
8-36
Figure 8-8: Detailed Row-Matching Algorithm
Box
• 3. Common 8-bit Segment Values in Dotted
Decimal Notation
– Segment
Decimal Value
00000000
0
11111111
255
• 4. Example
– 255.255.255.0 is 24 ones followed by 8 zero
– 255.255.255.0 is also called /24 in “prefix notation”
8-37
Figure 8-8: Detailed Row-Matching Algorithm
Box
Row
Destination
Mask
…
…
…
1
10.7.3.0
255.255.255.0
…
…
…
• Example 1: A Destination IP Address that is in the Range
• Destination IP Address of Arriving Packet
10.7.3.47
• Apply the Mask
255.255.255.0
• Result of Masking
10.7.3.0
• Destination Value
10.7.3.0
• Does Destination Value Match the Masking Result?
Yes
• Conclusion
Row 1 is a
match.
8-38
Figure 8-8: Detailed Row-Matching Algorithm
Box
Row
Destination
Mask
…
…
…
1
10.7.3.0
255.255.255.0
…
…
…
• Example 2: A Destination IP Address that is NOT in the Range
• Destination IP Address of Arriving Packet
10.7.5.47
• Apply the Mask
255.255.255.0
• Result of Masking
10.7.5.0
• Destination Value
10.7.3.0
• Does Destination Value Match the Masking Result?
No
• Conclusion
Row 1 is NOT
a match.
8-39
Figure 8-9: Interface and Next-Hop Router
Box
• Switches
– A switch port connects directly to a single computer or
another switch
– Sending the frame out a port automatically gets it to the
correct destination
Frame
8-40
Figure 8-9: Interface and Next-Hop Router
Box
• Routers
– Router ports (interfaces) connect to subnets, which have
multiple hosts and that may have multiple routers
– The packet must be forwarded to a specific host or router
on that subnet
Host
IP
Packet
Host
Subnet
on Router
Interface
Next-Hop
Router
8-41
Figure 8-9: Interface and Next-Hop Router
Figure 8-9:
Interface and Next-Hop Router
Next-Hop
Router
Interface (port)
Router
Forwarding
Packet
Router A
Box
Next-Hop Router
Packet to Router B out Interface 5
IP Subnet on
Interface (Port) 5
Possible
Next-Hop
Router
Router B
Router C
Packet must be sent to
a particular host or
router
Possible
Destination
Host
Possible
Next-Hop
Router
Best-match row has both an interface (indicating a subnet)
and also a next-hop router value to indicate a host or router on the subnet.
(Not just a Next Hop Router Column)
8-42
Routing table at your PC (10.10.34.161)
8-43
Routing Table (details)
8-44
Dynamic Routing
Protocols
Dynamic Routing Protocol
Routing Table Information
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Routing
– Routers constantly exchange routing table information
with one another using dynamic routing protocols
– Note that the term routing is used in two ways In
TCP/IP
• For IP packet forwarding and
• For the exchange of routing table information
through routing protocols
Dynamic Routing Protocol
Routing Table Information
8-46
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Autonomous System
– An organization’s internal network (internet)
• Interior Dynamic Routing Protocols
– Within an Autonomous System, firms use interior
dynamic routing protocols
• Exterior Dynamic Routing Protocols
– Between Autonomous Systems, companies use an
exterior dynamic routing protocol
8-47
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Interior Dynamic Routing Protocols
– As just discussed, within an Autonomous System,
firms use interior dynamic routing protocols
– The organization can freely select an interior routing
protocol
• RIP
• OSPF
• EIGRP
• Etc.
8-48
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Routing Information Protocol (RIP)
– Simple interior dynamic routing protocol from the IETF
– Low-cost management
– Poor efficiency: metric is merely the number of router
hops to the destination host
• No way to select cheapest route, etc.
– Weak security
– Useful only in small firms
8-49
8-50
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Open Shortest Path First
– Sophisticated IETF interior dynamic routing protocol
– Very efficient, having a complex metric based on a
mixture of cost, throughput, and traffic delays
– Strong security
– High management costs
– The only IETF dynamic routing protocol that makes
sense for all but the smallest networks
8-51
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Enhanced Interior Gateway Routing Protocol
(EIGRP)
– Proprietary interior dynamic routing protocol from
Cisco Systems
– “Gateway” is an obsolete term for “router”
– Very efficient because metric is a mixture of interface
bandwidth, load on the interface (0% to 100% of
capacity), delay, and reliability (percentage of packets
lost).
8-52
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Enhanced Interior Gateway Routing Protocol
(EIGRP)
– Only interior dynamic routing protocol that supports
multiprotocol routing (not just TCP/IP): IPX/SPX, SNA,
etc.
– But to use it, a company must buy Cisco routers
8-53
Figure 8-10: Dynamic Routing Protocols
(Study Figure)
• Exterior Dynamic Routing Protocols
– Between autonomous systems, companies use an
exterior dynamic routing protocol
– An organization is not free to select an exterior routing
protocol
• It must select a protocol selected by its ISP
– Border Gateway Protocol (BGP) is the main exterior
routing protocol
• Recall that “gateway” is the old term for “router”
8-54
Figure 8-11: Dynamic Routing Protocols
Figure 8-11: Dynamic Routing Protocols
Internal
Router
RIP,
OSPF, or
Internal
EIGRP
Router
RIP, OSPF, and EIGRP
Interior Dynamic Routing Protocols
Border
Router
Autonomous System
Recap
RIP,
OSPF, or
EIGRP
BGP Is an Exterior Dynamic
Routing Protocol
Autonomous System
Border
Router
8-55
The Address
Resolution Protocol
(ARP)
Figure 8-12: Address Resolution Protocol (ARP)
Figure 8-12: Address Resolution Protocol (ARP)
Packet
ARP Cache:
Known
IP addressEthernet
Address
Pairs
Frame
Originating
Router
1.
Broadcast ARP Request Message:
Host
"IPThe
HostSituation:
110.19.8.17,
110.19.8.47
whatwishes
is your 48-bit
MAC
address?"
The router
to pass
the
packet to
the
does not respond to
destination
host or to a next-hop router.
Router
B
ARP Request.
The router
knows the destination IP address of the target.
110.19.8.
notmust
reply learn the target’s MAC layer address
Thedoes
router
in order to be able to send the packet to the target in a frame.
Host
The router uses the Address Resolution Protocol
(ARP)
110.19.8.17
2.
ARP Response Message:
"My MAC address is A7-23-DA-95-7C-99".
replies.
8-57
Figure 8-12: Address Resolution Protocol (ARP)
Figure 8-12: Address Resolution Protocol (ARP)
ARP Cache:
Known
IP addressEthernet
Address
Pairs
1: Router broadcasts ARP Request to all
hosts and routers on the subnet.
Originating
Router
1.
Broadcast ARP Request Message:
"IP Host 110.19.8.17,
what is your 48-bit MAC address?"
Router B
110.19.8.
does not reply
2.
ARP Response Message:
"My MAC address is A7-23-DA-95-7C-99".
Host
110.19.8.47
does not respond to
ARP Request.
Host
110.19.8.17
replies.
8-58
Figure 8-12: Address Resolution Protocol (ARP)
Figure 8-12: Address Resolution Protocol (ARP)
ARP Cache:
Known
IP addressEthernet
Address
Pairs
2: ARP Reply sent by the host with the
target IP address.
Other hosts ignore it.
Originating
Router
1.
Broadcast ARP Request Message:
"IP Host 110.19.8.17,
what is your 48-bit MAC address?"
Router B
110.19.8.
does not reply
2.
ARP Response Message:
"My MAC address is A7-23-DA-95-7C-99".
Host
110.19.8.47
does not respond to
ARP Request.
Host
110.19.8.17
replies.
This is the
Destination host
8-59
Figure 8-12: Address Resolution Protocol (ARP)
Figure 8-12: Address Resolution Protocol (ARP)
ARP Cache:
Known
IP addressEthernet
Address
Pairs
3. Router puts the MAC address in its ARP
cache; uses it for subsequent packets to the host
Originating
Router
1.
Broadcast ARP Request Message:
"IP Host 110.19.8.17,
what is your 48-bit MAC address?"
Router B
110.19.8.
does not reply
2.
ARP Response Message:
"My MAC address is A7-23-DA-95-7C-99".
Host
110.19.8.47
does not respond to
ARP Request.
Host
110.19.8.17
replies.
8-60
8-61
arp
arp
arp
arp
arp
-a
-d 10.10.34.235
-d *
–s 157.55.85.212
-?
00-aa-00-62-c6-09
C:\>arp -a
Interface: 10.10.34.169 --- 0x2
Internet Address
Physical Address
Type
10.10.34.231
00-12-cf-28-cd-20
dynamic
10.10.34.234
00-12-cf-29-c6-80
dynamic
10.10.34.235
00-12-cf-28-1e-20
dynamic
10.10.34.238
00-12-cf-28-4d-e0
dynamic
10.10.34.239
00-12-cf-25-23-40
dynamic
10.10.34.240
00-12-cf-28-bf-e0
dynamic
10.10.34.254
00-08-e3-dd-b3-1f
dynamic
C:\>arp -s 10.10.34.235 00-12-cf-28-1e-20
C:\>arp –a
Interface: 10.10.34.169
Internet Address
10.10.34.235
10.10.34.254
--- 0x2
Physical Address
00-12-cf-28-1e-20
00-08-e3-dd-b3-1f
Type
static
dynamic
Multiprotocol Label
Switching (MPLS)
Figure 8-13: Multiprotocol Label
Switching (MPLS)
• Routers are Connected in a Mesh
– Multiple alternative routes make the choice of an
outgoing interface very expensive
• PSDNs (Chapter 7) also are Arranged in a Mesh
– However, a best path (virtual circuit) is set up before
transmission begins
– Once a VC is in place, subsequent frames are handled
quickly and inexpensively
• MPLS Does Something Like this for Routers
8-64
Figure 8-13: Multiprotocol Label
Switching (MPLS)
• MPLS Adds a Label Before Each Packet
– Label sits between the frame header and the IP
header
– Contains an MPLS label number
– Like a virtual circuit number in a PSDN frame
– Label-switching router merely looks up the MPLS
label number in its MPLS table and sends the packet
back out
IP
Packet
MPLS
Label
Data Link
Header
8-65
Figure 8-13: Multiprotocol Label
Switching (MPLS)
• Advantages of MPLS
– Router does a simple table lookup. This is fast and
therefore inexpensive per packet handled
• As fast as Ethernet switching!
– Can use multiple label numbers to give to traffic
between sites for multiple levels of priority or quality of
service guarantees
– MPLS supports traffic engineering: balancing traffic on
an internet
8-66
Figure 8-13:
Multiprotocol Label Switching (MPLS)
Figure 8-13: Multiprotocol Label Sw itching (MPLS)
Label-Switching
Router 1
Label-Switching
First router Router 2
adds the label
Legend
Packet Label
Label-Switching Table
Label Interface
A
1
C
1
F
3
LabelSwitching
Router 3
Label-Switching
Last router
Router 4
drops the label
Label-Switching
Router 5
Label-Switched
Path
MPLS reduces forwarding costs and permits traffic engineering,
including quality of service and traffic load balancing
8-67
The Domain Name
System (DNS)
Figure 8-14: Domain Name System (DNS)
Hierarchy
Figure 8-14: Domain Name System (DNS) Hierarchy
(root)
Top-Level
Domain
Names
.edu
.org
.net
A domain is a group of resources
.au of.ie
.nl
.com
.uk
under
the control
an organization.
Second-Level
The domain name system is a
Domain
general system
hawaii.edu Names microsoft.com
cnn.comfor managing names.
It is a hierarchical naming system.
cba.hawaii.edu
voyager.cba.hawaii.edu
Subnet Name
Queries to a DNS server can get
Information about a domain.
Host Names ntl.cba.hawaii.edu
8-69
Figure 8-14: Domain Name System (DNS)
Hierarchy
Figure 8-14: Domain Name System (DNS) Hierarchy
(root)
Top-Level
Domain
Names
.edu
.org
.net
.com
.au
.ie
.nl
.uk
Second-Level
The highest level is called the root.
Domain
hawaii.edu Names microsoft.com
There are 13cnn.com
DNS Root Servers.
They point to lower-level servers.
cba.hawaii.edu
voyager.cba.hawaii.edu
Subnet Name
Host Names ntl.cba.hawaii.edu
8-70
Figure 8-14: Domain Name System (DNS)
Hierarchy
Figure 8-14: Domain Name System (DNS) Hierarchy
(root)
Top-Level
Domain
Names
.edu
.org
.net
.com
Second-Level
Domain
hawaii.edu Names microsoft.com
cba.hawaii.edu
voyager.cba.hawaii.edu
.au
.ie
.nl
.uk
cnn.com
Top-level domains are
generic TLDs (.com, .net., .org, etc.) or
country TLDs (.ca, .uk, .ie, etc.)
Subnet Name
Host Names ntl.cba.hawaii.edu
8-71
Figure 8-14: Domain Name System (DNS)
Hierarchy
Figure 8-14: Domain Name System (DNS) Hierarchy
(root)
Top-Level
Domain
Names
.edu
.org
.net
.com
Second-Level
Domain
hawaii.edu Names microsoft.com
cba.hawaii.edu
voyager.cba.hawaii.edu
.au
Organizations seek
good secondlevel domain
names
.nl
.ie
.uk
cnn.com
Subnet Name
cnn.com
microsoft.com
hawaii.edu
etc.
Get them from
address registrars
Host Names ntl.cba.hawaii.edu
8-72
Figure 8-14: Domain Name System (DNS)
Hierarchy
Figure 8-14: Domain Name System (DNS) Hierarchy
(root)
Top-Level
Domain
Names
.edu
.org
.net
.com
.au
.ie
.nl
.uk
Second-Level
Host names are the bottom
Domain
the DNS hierarchy.
hawaii.edu Names microsoft.com ofcnn.com
cba.hawaii.edu
voyager.cba.hawaii.edu
A DNS request for a host name
will return its IP address.
Subnet Name
Host Names ntl.cba.hawaii.edu
8-73
The Internet Control
Message Protocol
(ICMP)
Figure 8-15: Internet Control Message Protocol
(ICMP) for Supervisory Messages
Figure 8-15: Internet Control Message Protocol (ICMP) for Supervisory Messages
Host Unreachable
Error Message
Echo Request
(Ping)
Router
ICMP
IP
Message Header
Echo
ICMP isResponse
the supervisory protocol
at the internet layer.
ICMP messages are encapsulated in the
data fields of IP packets
8-75
Figure 8-15: Internet Control Message Protocol
(ICMP) for Supervisory Messages
Figure 8-15: Internet Control Message Protocol (ICMP) for Supervisory Messages
Host Unreachable
Error Message
Router
Echo Request
ICMP
IP
When an error occurs,
the
device
Message Header
(Ping)
noting the error
may try to respond with an
Echo
ICMP error Response
message describing the problem.
ICMP error messages often are not sent
for security reasons because
attackers can use them to learn about a network
8-76
Figure 8-15: Internet Control Message Protocol
(ICMP) for Supervisory Messages
Figure 8-15: Internet Control Message Protocol (ICMP) for Supervisory Messages
To see if another host is active, a host
can send the target host an ICMP echo request
message (called a ping).
Host Unreachable
Router
If the
host
is active, it will send back an
Error
Message
echo response message confirming that it is active.
Echo
Response
Echo Request
(Ping)
ICMP
IP
Message Header
8-77
ICMP Type
8/0
3
4
5
11
12
13 / 14
17 / 18
Echo Request / Echo Reply
Destination Unreachable
Source Quench
Redirect
Time Exceeded
Parameter Problem
Timestamp Request / Timestamp Reply
Address Mask Request / Address Mask Reply
8-78
ICMP Message Formats
8-79
Figure 8-16: Dynamic Host
Configuration Protocol (DHCP)
• DHCP Gives Each Client PC at Boot-Up:
– A temporary IP Address
– A subnet mask
– The IP addresses of local DNS servers
• Better Than Manual Configuration
– If subnet mask or DNS IP addresses change, only the
DHCP server has to be updated manually
– Client PCs are automatically updated when they next
boot up
8-80
動態主機組態協定(DHCP)
• Dynamic Host Configuration Protocol
• 自動設定電腦的
– IP位址(163.22.20.223)
– 子網路遮罩(255.255.255.0)
– 預設通訊閘(163.22.20.254)
– 領域名稱伺服器(163.22.2.1)
– …
• winipcfg (Win 98/Me)
• ipconfig /all (Win 2000/XP)
8-81
1
2
3
控制台  網路和網際網路連線
8-82
8-83
ipconfig
ipconfig
ipconfig /all
ipconfig /release
ipconfig /renew
C:\>ipconfig
Windows IP Configuration
Ethernet adapter 區域連線:
Connection-specific
IP Address. . . . .
Subnet Mask . . . .
Default Gateway . .
DNS
. .
. .
. .
Suffix
. . . .
. . . .
. . . .
.
.
.
.
:
:
:
:
ncnu.edu.tw
10.10.34.169
255.255.255.0
10.10.34.254
8-84
The Internet
Protocol (IP)
Versions 4 and 6
IPv4 Packet
8-86
Figure 8-17: IPv4 and IPv6 Packets
Bit 0
IP Version 4 Packet
Bit 31
Version Header
Diff-Serv
Total Length
(4 bits) Length
(8 bits)
(16 bits)
Value (4 bits)
Length in octets
is 4
(0100)
Identification (16 bits)
Flags Fragment Offset (13 bits)
Unique value in each original
(3 bits)
Octets from start of
IP IPv4
packet
original
is the dominant version of IP
today.IP fragment’s
data field
The version number in its header is 4 (0100).
Time to Live
Protocol (8 bits)
Header Checksum
(8header
bits) length
1=ICMP,
6=TCP,
The
and total
length field tell the(16
sizebits)
of the packet.
17=UDP
The Diff-Serv field can be used for quality of service labeling.
(But MPLS is being used instead by most carriers)
8-87
Figure 8-17: IPv4 and IPv6 Packets
Bit 0
IP Version 4 Packet
Version Header
Diff-Serv
(4 bits) Length
(8 bits)
Value (4 bits)
is 4
(0100)
Identification (16 bits)
Unique value in each original
IP packet
Bit 31
Total Length
(16 bits)
Length in octets
Flags Fragment Offset (13 bits)
(3 bits)
Octets from start of
original IP fragment’s
data field
Time to Live
Protocol (8 bits)
Header Checksum
(8 bits)
1=ICMP, 6=TCP,
(16 bits)
17=UDP
The second row
is used for reassembling fragmented
IP packets, but fragmentation is quite rare,
so we will not look at these fields.
8-88
Figure 8-17: IPv4 and IPv6 Packets
The sender sets the time-to-live value (usually 64 to 128).
Each router along the way decreases the value by one.
A router decreasing the value to zero discards the packet.
Bit 0
IP Version 4 Packet
Bit 31
It may send an ICMP error message.
Version Header
Diff-Serv
Total Length
(4 bits)The
Length
(8 bits)
bits)
protocol field
describes the message(16
in the
data field
Value (4 bits)
Length in octets
(ICMP, TCP, UDP, etc.)
is 4
(0100)The header checksum is used to find errors in the header.
Identification
If a packet
(16 bits)
has an error,
Flags
the router
Fragment
dropsOffset
it.
(13 bits)
Unique value
There
in is
each
no retransmission
original
(3 bits)
at the internet
Octets layer,
from start of
IP packet
so the internet layer is still unreliable.
original IP fragment’s
data field
Time to Live
Protocol (8 bits)
Header Checksum
(8 bits)
1=ICMP, 6=TCP,
(16 bits)
17=UDP
http://www.iana.org/assignments/protocol-numbers
8-89
Traceroute
RFC 1393
• To provide a trace of the path the packet took to reach
the destination.
• Operates by first sending out a packet with a Time To
Live (TTL) of 1. The first hop then sends back an ICMP
error message indicating that the packet could not be
forwarded because the TTL expired.
• The packet is then resent with a TTL of 2, and the
second hop returns the TTL expired. This process
continues until the destination is reached.
• Record the source of each ICMP TTL exceeded
message
http://www.visualroute.com/ 8-90
8-91
8-92
8-93
Figure 8-17: IPv4 and IPv6 Packets
Bit 0
IP Version 4 Packet
Bit 31
Source IP Address (32 bits)
Destination IP Address (32 bits)
Options (if any)
Padding
Data Field
The source and destination IP addresses
Are 32 bits long, as you would suspect.
Options can be added, but these are rare.
8-94
Figure 8-17: IPv4 and IPv6 Packets
Bit 0
Version
(4 bits)
Value
is 6
(0110)
Diff-Serv
(8 bits)
IP Version
6 is the emerging
IP Version
6 Packet
Bit 31
version of the Internet protocol.
Flow Label (20 bits)
Marks
a packet
as part offor
a specific flow
Has 128
bit addresses
an almost unlimited number of IP addresses.
Growing fastest in Asia, which was
Payload Length
Hop Limit
short-changed inNext
IPv4Header
address allocations
(16 bits)
(8 bits) Name
(8 bits)
of next header
Source IP Address (128 bits)
Destination IP Address (128 bits)
Next Header or Payload (Data Field)
8-95
IPv6 Packet
8-96
IPv6 Header Fields (1)
• Version
–6
• Traffic Class (DS/ECN)
– Classes or priorities of packet
– Still under development
– See RFC 2460
• Flow Label
– Used by hosts requesting special handling
• Payload length
– Includes all extension headers plus user data
8-97
IPv6 Header Fields (2)
• Next Header
– Identifies type of header
• Extension or next layer up
• Source Address
• Destination address
8-98
Types of address
• Unicast
– Single interface
• Anycast
– Set of interfaces (typically different nodes)
– Delivered to any one interface
– the “nearest”
• Multicast
– Set of interfaces
– Delivered to all interfaces identified
8-99
Text Representation of IPv6 Addresses
• x:x:x:x:x:x:x:x
RFC 3513
• hexadecimal values of the eight 16-bit
pieces of the address.
– FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
– 1080:0:0:0:8:800:200C:417A
8-100
IPv6 Address Representation (2)
• The use of "::" indicates multiple groups of 16bits of zeros.
• Unicast address
– 1080:0:0:0:8:800:200C:417A
– 1080::8:800:200C:417A
• Multicast address
– FF01:0:0:0:0:0:0:101  FF01::101
• Loopback address
– 0:0:0:0:0:0:0:1
 ::1
• unspecified addresses (Absence of address)
– 0:0:0:0:0:0:0:0
 ::
8-101
IPv6 Address Representation (3)
• IPv4 and IPv6 mixed address
– x:x:x:x:x:x:d.d.d.d
– x: IPv6, d: IPv4
– Eg.
• 0:0:0:0:0:FFFF:129.144.52.38
• ::13.1.68.3
• ::FFFF:129.144.52.38
8-102
The Transmission
Control Protocol (TCP)
Figure 8-18: TCP Segment and UDP Datagram
Bit 0
TCP Segment
Source Port Number (16 bits)
Bit 31
Destination Port Number (16 bits)
Sequence Number (32 bits)
Acknowledgment Number (32 bits)
Header
Length
(4 bits)
Reserved
The source
Flagand
Fields
destination portWindow
numbers
Size
(6 bits)
specify a(6
particular
bits)
application on
(16the
bits)
source and destination multitasking computers
(Discussed later)
TCP Checksum (16 bits)
Urgent Pointer (16 bits)
Sequence numbers are 32 bits long.
Flag fields are one-bit fields. They include SYN, ACK, FIN,
So are acknowledgment numbers.
and RST.
8-104
Figure 8-18: TCP Segment and UDP Datagram
Flags are one-bit fields.
Bit 0
TCPvalue
Segment
Bit 31
If a flag’s
is 1, it is “set”.
If a flag’s
value isDestination
0, it is “not Port
set.”Number (16 bits)
Source Port Number
(16 bits)
TCP has six flags
Sequence Number (32 bits)
If the TCP Checksum field’s value is correct,
The receiving process sends back an acknowledgment.
Acknowledgment Number (32 bits)
Header
Length
(4 bits)
Reserved Flag Fields
(6 bits)
(6 bits)
TCP Checksum (16 bits)
Window Size
(16 bits)
Urgent Pointer (16 bits)
8-105
8-106
Figure 8-18: TCP Segment and UDP Datagram
For flow control (to
tell Segment
the other party to slow down),
TCP
Bit 31
The sender places a small value in the Window Size field.
Source Port Number (16 bits)
Destination Port Number (16 bits)
If the Window Size is small, the receiver will have to stop transmitting
Sequence
Number
(32 a
bits)
after a few more segments
(unless
it gets
new acknowledgment
extending the number of segments it may send.)
Acknowledgment Number (32 bits)
Bit 0
Header
Length
(4 bits)
Reserved Flag Fields
(6 bits)
(6 bits)
TCP Checksum (16 bits)
Window Size
(16 bits)
Urgent Pointer (16 bits)
8-107
Figure 8-18: TCP Segment and UDP Datagram
Bit 0
TCP Segment
Options (if any)
Bit 31
Padding
Data Field
TCP segment headers can end with options.
This is very common.
If an option does not end at a 32-bit boundary,
padding must be added.
8-108
The User Datagram
Protocol (UDP)
Figure 8-18: TCP Segment and UDP Datagram
Bit 0
UDP Datagram
Bit 31
Source Port Number (16 bits)
Destination Port Number (16 bits)
UDP Length (16 bits)
UDP Checksum (16 bits)
Data Field
UDP messages (datagrams) are very simple.
Like TCP, UDP has 16-bit port numbers.
The UDP length field allows variable-length application messages.
If the UDP checksum is correct, there is no acknowledgment.
If the UDP checksum is incorrect, the UDP datagram is dropped.
8-110
Figure 8-19: TCP Connection Openings and
Closings
• TCP is a connection-oriented protocol
– Each connection has a formal opening process
– Each connection has a formal closing process
– During a connection, each TCP segment is
acknowledged
• (Of course, pure acknowledgments are not
acknowledged)
8-111
Figure 8-19: TCP Connection Openings and
Closings
Normal Three-Way Opening
SYN
SYN/ACK
ACK
A SYN segment is a segment in which the SYN bit is set.
One side sends a SYN segment requesting an opening.
The other side sends a SYN/acknowledgment segment.
Originating side acknowledges the SYN/ACK.
8-112
Figure 8-19: TCP Connection Openings and
Closings
Normal Four-Way Close
FIN
ACK
FIN
ACK
A FIN segment is a segment in which the FIN bit is set.
Like both sides saying “good bye” to end a conversation.
8-113
Figure 8-19: TCP Connection Openings and
Closings
Abrupt Reset
RST
An RST segment is a segment in which the RST bit is set.
A single RST segment breaks a connection.
Like hanging up during a phone call.
There is no acknowledgment.
8-114
Port Numbers and
Sockets in TCP and
UDP
TCP and UDP Port Numbers
• Computers are multitasking devices
– They run multiple applications at the same time
– On a server, a port number designates a specific
applications
HTTP Webserver
Application
SMTP E-Mail
Applications
Port 80
Port 25
Server
8-116
Range of TCP (and UDP) Port Numbers
• 0~1023
– The range for assigned ports managed by the IANA
• 1024~49151
– Registered Port Numbers
– For non-major applications.
– Unix does not follow the rule.
• Uses some of these port numbers as ephemeral port
numbers.
• 49152~65535
– Ephemeral Port Numbers
– Dynamic and/or Private Ports
• Port numbers:
– http://www.iana.org/assignments/port-numbers
8-117
TCP and UDP Port Numbers
• Major Applications Have Well-Known Port Numbers
– 0 to 1023 for both TCP and UDP
– HTTP is TCP Port 80
– SMTP is TCP Port 25
HTTP Webserver
Application
SMTP E-Mail
Applications
Port 80
Port 25
Server
8-118
TCP and UDP Port Numbers
• Clients Use Ephemeral(短暫的) Port Numbers
– 1024 to 4999 for Windows Client PCs
– A client has a separate port number for each connection
to a program on a webserver
E-Mail
Application
on Mail
Server
Webserver
Application
on Webserver
Port 4400
Port 3270
Client
8-119
Figure 8-20: Use of TCP (and UDP) Port Numbers
A socket is an
IP address, a colon, and a port number.
Client 60.171.18.22
1.33.17.3:80
123.30.17.120:25
128.171.17.13:2849
It represents a specific application (Port number)
on a specific server (IP address)
Or a specific connection on a client.
Client PC
128.171.17.13
Port 2849
Webserver
1.33.17.13
Port 80
SMTP Server
123.30.17.120
Port 25
8-120
Figure 8-20: Use of TCP (and UDP) Port Numbers
Client 60.171.18.22
From: 60.171.18.22:2707
To: 1.33.17.13:80
This shows sockets for a client
packet sent to a webserver application
on a webserver
Webserver
1.33.17.13
Port 80
SMTP Server
123.30.17.120
Port 25
8-121
Figure 8-20: Use of TCP (and UDP) Port Numbers
Client 60.171.18.22
From: 60.171.18.22:2707
To: 1.33.17.13:80
From: 1.33.17.13:80
To: 60.171.18.22:2707
Sockets in
two-way
transmission
Webserver
1.33.17.13
Port 80
SMTP Server
123.30.17.120
Port 25
8-122
Figure 8-20: Use of TCP (and UDP) Port Numbers
Client 60.171.18.22
From: 60.171.18.22:2707
To: 1.33.17.13:80
From: 1.33.17.13:80
To: 60.171.18.22:2707
From: 60.171.18.22:4400
To: 123.30.17.120:25
Clients use a different ephemeral
Port number for different connections
Webserver
1.33.17.13
Port 80
SMTP Server
123.30.17.120
Port 25
8-123
Layer 3 Switches
Figure 8-21: Layer 3 Switches and Routers
in Site Networks
Figure 8-21: Layer 3 Sw itches and Routers in Site Internets
L3
To
Other
Sites
Layer 3
Switch
L3
Router
Layer 3 switches are
faster and cheaper to
buy than traditional
routers.
However, they are
usually limited in
functionality.
Layer 3
Switch
Ethernet Workgroup
Switch
Layer 3 switches are
routers.
Ethernet Workgroup
Switch
They also are
expensive to manage.
They are typically
used between
Usually too expensive to replace workgroup switches.
Usually too limited in functionality to replace border routers.
Replaces core switches in the middle.
8-125
Topics Covered
Topics Covered
• Internetworking Recap from Earlier Chapters
– Internetworking involves the internet and transport layers
– Packets are encapsulated in frames in single networks.
– Transport layer is end-to-end
– Internet layer is hop-by-hop between routers
– IP, TCP, and UDP are the heart of TCP/IP
internetworking
8-127
Topics Covered
• Hierarchical IP Address parts
– Network, subnet, and host parts
• Router Operation
– Border routers connect networks
– Internal routers connect subnets
– We focused on TCP/IP routing, but multiprotocol routing
is crucial
– Router meshes give alternative routes, making routing
very expensive
8-128
Topics Covered
• Routing of Packets
• Routing tables
• IP address range governed by a row—usually a route
to a network or subnet
• Metric to help select best matches
• Next-hop router to be sent the packet next
– Can be a local host on one of the router’s subnets
– Process
• Final all possible routes through row matching
• Select by length of match, then metric if tie
• Send out to next-hop router in the best-match row
8-129
Topics Covered
Box
• Detailed Look at Routing Decisions
• IP address range
– Destination
– Mask
– If the masked destination IP address in an arriving
packet matches the destination value, the row is a
match
• Next-Hop Router
– Interface
– Next-hop router or destination host
8-130
Topics Covered
• Dynamic Routing Protocols
• Interior dynamic routing protocols within an
autonomous system
– RIP, OSPF, EIGRP
• Exterior dynamic routing protocols between
autonomous systems
– BGP
• Address Resolution Protocol
– Router knows the IP address of the next-hop router or
destination host
– Must learn the data link layer address as well
8-131
Topics Covered
• Multiprotocol Label Switching
– Routing decisions are based on labels rather than
destination IP addresses
– Reduces routing costs
• Domain Name System (DNS)
– General hierarchical naming system for the Internet
• Internet Control Message Protocol (ICMP)
– General supervisory protocol at the internet layer
– Error advisements and Pings (echo requests/replies)
8-132
Topics Covered
• The Internet Protocol (IP)
– Detailed look at key fields
– Protocol field lists contents of the data field
– 32-bit IP addresses
– IPv4 is the current version
– IPv6 offers 128-bit IP addresses to allow many more IP
addresses to serve the world
8-133
Topics Covered
• The Transmission Control Protocol (TCP)
– Sequence and acknowledgement numbers
– Flag fields that are set or not set
– Window size field allows flow control
– Options are common
– Three-way openings (SYN, SYN/ACK, and ACK)
– Four-way normal closings (FIN, ACK, FIN, ACK)
– One-way abrupt closing (RST)
8-134
Topics Covered
• The User Datagram Protocol (UDP)
– Simple four-field header
• Port Numbers and Sockets in TCP and UDP
– Applications get well-known port numbers on servers
– Connections get ephemeral port numbers on clients
– Socket is an IP address, a colon, and a port number
– This designates a specific application (or connection) on
a specific server (or client)
• Layer 3 Switches
– Fast, inexpensive, and limited routers
8-135