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TCP/IP networking 1-1
TCP/IP networking
TCP/IP A networking protocol suite
• Use several protocols, main ones are tcp and ip.• IP stands for Internet Protocol • TCP stands for Transmission Control Protocol.
The native language of the InternetSupported by most OSs (Unix, MacOS,
Windows, Netware, etc)Defines a uniform programming interface to
different types of network hardware
TCP/IP networking 1-2
TCP/IP and Internet
1969 ARPAnet Experimental packet-switching network Study robust, reliable, vendor-independent data
communication Very successful
1975 ARPAnet became operation network Development continuing TCP/IP was developed
1983 TCP/IP protocols were adopted as Military Standards TCP/IP was implemented in Berkeley Unix. ARPAnet was divided into MILNET and ARPAnet
TCP/IP networking 1-3
TCP/IP and Internet
1985 NSFNet Connected to the then existing Internet
( MILNET plus ARPAnet) Linked together the five NSF super
computer centers Wanted to extend the network to every
scientist 1987 new NSFNet backbone
Faster Three-tiered topology: backbone, regional
networks, and local networks.
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TCP/IP and Internet
1990 ARPAnet passed out of existence 1995 NSFnet ceased its role as a primary
Internet backbone network Today Internet is build by commercial
providers. Infrastructure is being created by
• National network provider, caller tier-one providers• Regional network provider
Local access and user services is provided by Internet Service Providers (ISPs)
Network Access Points (NAPS): major interconnection points
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TCP/IP and Internet How the internet is managed today
Commercial force Several organization
• Internet Corporation for Assigned Names and Numbers (ICANN)
– www.icann.org
• Internet Engineering Task Force (IETE) – www.ietf.org
• Internet Society (ISOC)– www.isoc.org
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TCP/IP and Internet
Network standards and documentation Request for Comments (RFC)
• Over 4000 has been created• FY• STD• BCP
Dispatch central for RFC-related matters• www.rfc-editor.org
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Networking Road Map
TCP/IP components IP, the Internet Protocol
• routes data packets from one machine to another ICMP, the Internet Control Message Protocol
• Provides several kinds of low-level support for IP– Error message
– Routing assistance
– Debugging help
ARP, the Address Resolution Protocol• Translates IP addresses to hardware addresses
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Networking Road Map
UDP, the User Datagram Protocol • Delivers data to specific applications on the
destination machine• Provides “unverified”, “best effort” transport for
individual messages TCP, the Transmission Control Protocol
• Delivers data to specific applications on the destination machine
• Provides reliable, flow controlled, error corrected conversation between processes on two hosts.
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TCP/IP network model
UTP copper, fiber, radia waves
ARP, Device Drivers
IP ICMP
TCP UDP
ARP SSH, FTP, WEB DNS, Quake Traeroute
Physical layer
Link Layer
Network Layer
Transport Layer
Application Layer
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Packets and encapsulation
Data travels on a network in the form of packets
Each packet consists of A header – where it came from and where it’s going,
protocol info, checksum, etc. A payload - data
As a packet travels down the protocol stack encapsulation
• Each protocol adds its own header information• Each protocol’s finished packet becomes the payload
part of the packet generated by the next protocol.
On a receiving machine, the encapsulation is reversed as the packet travels back up the protocol stack.
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Packets and Encapsulation
Example: A typical network packet
Ethernet header
IP header
UDP header
Application dataEthernet CRC
UDP packet(108 bytes)
IP packet(128bytes)
Ethernet frame(146 bytes)
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Addressing
Packets addressing Packets must be properly addressed in order to
reach their destination Addressing schemes
• MAC (media access control) addresses for hardware• IP addresses for software• Hostnames for people
Ports 16 bit number Address particular processes or services Well-known ports are defined in /etc/services Unix systems restrict access port under 1024 to root.
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Addressing
Address types Unicast – addresses that refer to a single host
(interface) Multicat – addresses that identify a group of hosts Broadcast – addresses that include all hosts on the
local network IP addresses
Four bytes long Network part and host part Written as decimal numbers, one for each byte
separated by periods When 127 is the first byte of an address, it denotes
the “loopback network”• Lookback address 127.0.0.1 - localhost
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Addressing
IP address classes The traditional class determine which bytes
of the address were in the network portion and which were in the host portion
• A 1-126 N.H.H.H Very early network• B 128-191 N.N.H.H large sites (65536)• C 192-223 N.N.N.H (256)• D 224-239 Multiple addresses• E 240- 254 Experimental
addresses
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Addressing
Subnetting and netmasks Host portion of an address is “borrowed” to
extend the network portion This reassignment is done by using ifconfig
command to associate an explicit “subnet mask” with a network interface.
Each bit of the netmask that corresponds to the network portion of an IP address is set to 1, host bits are set to 0
• The division of network part and host part need not fall on a byte boundary
• Network bits must be contiguous and must appear at the high order end of the addresses
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Addressing
Notation• Ipaddress netmask• Ipaddress/length of the network part
– 128.138.243.0/26 Example
• 128.138.243.100/24– Netmask? – Network?– Broadcast?
• 128.138.243.100/26 100=01100100– Netmask?– Network?– Broadcast?
Use ipcalc to get the values.
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Addressing
The IP address crisis Fundamental problems with the original
class allocating scheme• Run out of B classes• Routing table were growing so large• IP address were allocated on a first-com, first-
served basis with no locality of reference solutions
• Short term: Classless Inter-Domain Routing (CIDR)• IPV6: extend the address to 16 bytes
– 665,570,793,348,866,943,898,599 addresses
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Addressing
Address allocation Regional IP address registries
• ARIN North and South America• APNIC Asia/Pacific region• RIPE Europe and surrounding
areas
Private addresses Packets bearing private addresses can not
get into internet IP address reserved for private use
• 10.0.0.0/8• 172.16.0.0/12• 192.168.0.0/16
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Routing
Routing is the process of directing a packet through the maze of networks that stand between its source and its destination.
Routing info is stored in a table in the kernel. Examine it use “netstat –r” Configure dynamically Configure statically#route add –net 132.236.220.64 netmask 255.255.255.192
132.236.212.6#route add default 132.236.227.1
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ARP
The address Resolution Protocol discovers the hardware address associated with a particular IP address.
APR uses broadcast packets, cannot cross networks “Does anyone know the hardware address for
128.138.116.4”? Check the arp cache table with arp command
#/usr/sbin/arp –a RARP
Reverse translation Query a central server to discover its own address Need configuration
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Additions of machines to a network Basic steps are
Assign a IP address and hostname Set up the new host to configure its network
interfaces at boot time Set up a default route and perhaps fancier
routing Point to a DNS name server, to allow access
to the rest of the Internet. Debugging
• Always to reboot if changes affect booting
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Assigning hostnames and IP addresses Mapping hostnames to IP
Hosts file NIS or NIS+ DNS Or Combination above
Hosts file /etc/hosts
• Each line start with IP, continues with various symbolic names by which that address is known.
• Entries– Localhost, gateway, special hosts, …
• Replicate same hosts file on machines
Configure hostname Command hostname run at the boot time Configuration file
TCP/IP networking 1-23
Assigning hostnames and IP addresses Configure network interfaces: ifconfig
Enable or disable network interface Set IP address Set subnet mask Set other options Run at the boot time (use command with
the value from configure files ) Format
• $ifconfig interface address options … up|down• Ex:#ifconfig eth0 128.138.240.7 network 255.255.255.0 up
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Assigning hostnames and IP addresses Interface name:
Identifies the hardware to which the command applies
Two or three character device name followed by a number.
The loopback interface is named lo0 The common interface names are
• Ie0, le0, ln0, we0, hme0, eri0, lan0, …
Display the interfaces $netstat –i
Display the setting of interfaces $ifconfig –a
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Assigning hostnames and IP addresses Configure the network interface
The ifconfig commands support many options • Specify address • Specify netmask, otherwise it uses address class
(A,B,C)• Specify broadcast
– Default can be calculated from IP + netmask– Some sites set it to avoid certain types of denial of service
attacks. Not good. • Activate or deactivate the device driver
– Use keywork up, down. Ifconfig allows you to configure a interface card by
hand, but the value is only in kernel.• To make it survive the reboot, change the right
configuration file
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Configure static routes
Command route defines static routes Static route will stay in the routing table in
most case configure the default routing when adding a
host to local network Routing is performed at what layer?
• The packets’ destination IP is compared with the route , if it matches, the packet is forwarded to the “next gateway” IP address associated with that route
• Routing added when configure the interface - Packets destined for host on a directory connected network
• Default route is invoked when there is no route that matches the destination address.
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Configure static routes
The format:• #route op [type] destination gateway [hop-count]• Where
– Op: add, delete, get, change, flush, monitor– Destination: host address, network address, or the
keyword “default” ( 0.0.0.0)– Gateway: a machine to which packets should be
forwarded» Must be on a directly connected network» Forwarding can only be performed one hop at a time
– Type: -net, -host Check the routing table:
• #netstat -nr
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Configure static routes
default route• #route add default gateway_ip_address• Change the configure file
– Solaris: /etc/defaultrouter
– Hp-UX: /net/rc.config.d/netconf
– Redhat: /etc/sysconfig/network
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Configuring DNS
To configure a machine as a DNS client Configure /etc/resolv.conf
• List DBS domains that should be searched to resolve name that are incomplete
• Line the IP addresses of the name servers to contact for name lookups
• Example:[ruihong@dafinn ~]$ more /etc/resolv.conf
search cs.mtu.edu csl.mtu.edu mtu.edu
nameserver 141.219.152.253
nameserver 141.219.152.254
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Configuring DNS
Configure the service switch file• Which one take effect? /etc/hosts, NIS, DNS?• Solaris, Hp-UX, Redhat: /etc/nsswitch.conf • Example:
hosts: files nis dns
• Clause: [NOTFOUND=return]
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Network configuration files by system All
/etc/hosts /etc/recolv.conf
Solaris /etc/hostname.ifname /etc/nodename /etc/defaultrouter /etc/inet/netmasks /etc/inet/hosts
HP-UX /etc/rc.config.d/netconf
Red Hat /etc/sysconfig/network Network-scripts/ifcfg-ifname
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Practice Check
IP address/netmask/broadcast route Arp table Hostname DNS
Modify Hostname Dns research list
• Ping wopr Dns servers Remote default route
• Ping wopr Add the default route back again
Reboot
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DHCP
Dynamic Host Configuration Protocol Distribute network and administrative
parameters to DHCP client, include• IP address and netmasks• Gateways • DNS name servers• Syslog hosts• WINs Servers, X font servers, proxy servers, NTP
servers• TFTP servers ( for loading a boot image)• And more…
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DHCP
How DHCP works Client sends “Who am I” DHCPDISCOVER
message • To broadcast 255.255.255.255• With 0.0.0.0 as its own address
Server responds with OFFER messages Client sends back a REQUEST messages Server responds with ACK or NAK
Client renew the lease by sending another REQUEST message