Transcript presentation source

TCP/IP Internetting
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TCP/IP Internetting

Subnet layer
TCP/IP
OSI
Application
Transport
Internet
Subnet

Links stations on same subnet

Often IEEE LAN standards

PPP for telephone connections

TCP/IP specifies almost any subnet standard

For LANs, etc., specifies OSI

OSI further subdivides into Physical, Data Link
Data Link
Physical
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TCP/IP Internetting

Application
Transport
Internet
Subnet
Internet layer:
 Links
stations across internets
 Main
standard is the Internet Protocol (IP)
 Dominant
protocol for routers
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TCP/IP Internetting


Transport layer:
Application
Transport
Internet
Subnet

Links computers, even if different platforms

Main standards are Transmission Control Protocol
(TCP) and User Datagram Protocol (UDP)
Application layer:

Links application programs even if from different
vendors

Many standards, because many applications

SMTP for e-mail; HTTP for the WWW, etc.
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Universal Addressing

Each host has a unique IP Number

32-bit binary number

Goes in the IP header’s source and destination fields

10000000101010110001000100001101

Impossible to remember
IP Packet
Source
Destination
4 Bytes
4 Bytes
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Subnet Mask

Problem: IP numbers do not include subnetting

Solution: Create a second number: a Subnet Mask

Define which bits of the IP address refer to subnets
vs. hosts on subnet

Subnet mask is 32 bits long, in dot quad format

See the class meeting on Windows TCP/IP for
basic IP and Subnet Mask concepts.
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Routers

Routers also get IP addresses
 So
packets can be sent to them for routing
 Has network ID of the network on which it sits
 Must be assigned a host ID
 Example: 128.171.17.1
Default
Router
IP Packet
for Delivery
128.171.17.104
Another Router
128.171.17.1
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Routers

Subnets can have Multiple Routers
 There
is usually a default router for packet
delivery
 Default router is used if no router is specified
 Routers are sometimes called gateways in
TCP/IP
Default
Router
IP Packet
for Delivery
Other Router
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Routing Protocols
Routing
Table
There are no “master” routers.
Each router works independently to do routing.
This requires each router to build a “routing table” that
contains information about the locations of other routers.
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Routing Protocols
Routing
Table
Routing protocols allow
routers to exchange
information in their
routing tables.
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Peer Control Among Routers

Routers Communicate Among Themselves



To coordinate their actions without central control
Share knowledge of network connectivity
Common standards are RIP, OSPF, BGP
Router
Coordination
Message
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Routing Protocols

RIP - Router Information Protocol


OSPF - Open Shortest Path First


Optimizes routing, but complex
BGP - Border Gateway (Router) Protocol


High overhead, but simple and OK for small networks
Used in Internet Backbone Routers
Read Cisco routers for an overview
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Autonomous Systems
RIP
or
OSPF
Autonomous
Router
Organization can select any
routing protocol to synchronize
its autonomous (internal)
routers. RIP and OSPF are
common.
RIP
or
OSPF
Border routers that link
autonomous systems normally
use BPG.
BPG
Border Router
Border Router
Autonomous System
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Error Handling

TCP/IP a comprehensive set of error
handling processes

The Internet Control Message Protocol (ICMP) is used
to send error messages.

Hosts, Routers send ICMP messages to one another if a
problem occurs

“Host not found” is a common ICMP error message.
Host
ICMP Error Message
Router
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Internet Control Message
Protocol (ICMP)
The Internet Control Message Protocol (ICMP)
is for delivering supervisory messages
among hosts and routers
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Internet Control Message
Protocol (ICMP)
“Host Unreachable”
Error Messages
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Internet Control Message
Protocol (ICMP)
Flow Control
“Source Quench” tells host
to reduce transmission rate.
Source
Quench
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Internet Control Message
Protocol (ICMP)
“Echo
Request”
“Echo
Response”
Source host can ask questions of
destination hosts.
“Echo Request” asks if the other host
is reachable.
Destination host sends back
“Echo Response.”
Usually implemented with “Ping”
program.
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Autoconfiguration


Autoconfiguration Server has a bank of addresses

When a PC “logs in,” it gets a temporary IP number.

Popular standards are DHCP (in Windows NT) and RARP
Large stations receive permanent addresses
DHCP Request for Address
DHCP Response:
Your Temporary Address is
127.171.17.35
DHCP
Server
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Autoconfiguration Protocol
Source
Host
Autoconfiguration Request Message
AutoConfiguration
Host
Source host sends Autoconfigutation Request
Message to the autoconfiguration host
“My 48-bit MAC subnet address is X.
Please give me a 32-bit IP host address.”
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Autoconfiguration Protocol
Source
Host
AutoConfiguration
Autoconfiguration Response Message
Host
Autoconfiguration host sends back a
Autoconfiguration response message.
“Computer at MAC Address X,
your 32-bit IP host number is ‘110100…’.”
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Autoconfiguration Protocols

RARP: Reverse Address Resolution
Protocol
 Older

autoconfiguration protocol
Bootp
 Another

older protocol
DHCP
 Dynamic
 Built
Host Configuration Protocol
into Windows NT Server
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Domain Name Service

Hosts also have IP host names
 Voyager.cba.hawaii.edu
 Like
nicknames

IP packets require formal IP numbers to put
in their source and destination fields

If tell your software the IP host name, it
must look up the IP number
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Domain Name Service

Program knowing a host name sends
request to Domain Name Service (DNS)
Server; receives IP Number
DNS Request for
Voyager.cba.hawaii.edu
DNS
Server
DNS Response: 128.171.17.13
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Domain Name System (DNS)
Source
Host
DNS Request Message
DNS
Host
Source host sends DNS Request Message to DNS host.
“I need the 32-bit IP host number for the host named
voyager.cba.hawaii.edu.”
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Domain Name System (DNS)
Source
Host
DNS
Host
DNS Response Message
DNS host returns a DNS Reply Message.
“The 32-bit host number is 128.171.44.53”.
DNS
Host
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Domain Name System (DNS)
Source
Host

Each network has a DNS host
 May also have a secondary DNS host
 Network DNS host may only know the
IP names and numbers of local hosts on
the network
 For other IP names, contacts another
DNS host, especially root DNS hosts,
which should have extensive information
DNS
Host
DNS
Host
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