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1
Network LayerNetwork LayerLecture 12Lecture 12
Imran AhmedImran AhmedUniversity of Management & TechnologyUniversity of Management & Technology
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Agenda
• Introduction & Network layer functions
• Routing principles
• Hierarchical routing
• The Internet protocol (IP)
• Routing in the Internet
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BOOTP• Bootstrap protocol (BOOTP) is a client-server protocol
designed to provide the four types of information for a diskless computer or a computer that is booted for the first time.– Its IP address– Its subnet mask– The IP address of a router– The IP address of a name server
• This information is usually stored in a configuration file and accessed by a computer during bootstrap process.
• In case of diskless computer, the OS & the networking software could be stored in ROM.
• So, the above information cannot be stored in the ROM by the manufacturers.
• Do we need RARP in this case?
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DHCP• Dynamic Host Configuration Protocol (DHCP) is
a dynamic configuration protocol.• DHCP is compatible with BOOTP.• DHCP provides temporary IP addresses for a
limited period of time.• In the simplest case, each network will have a
DHCP server. If no server is present then a DHCP “relay agent” (typically a router) that knows the address of the DHCP server for that network is needed.
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DHCP Client-Server Scenario
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DHCP
• For new arriving host, the DHCP protocol is a four-step process:-
• DHCP server discovery
• DHCP server offers
• DHCP request
• DHCP ACK
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DHCP Client-Server Scenario
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Mapping IP Addresses to Hardware Addresses
• IP Addresses are not recognized by hardware.
• If we know the IP address of a host, how do we find out the hardware address ?
• The process of finding the hardware address of a host given the IP address is called
Address ResolutionAddress Resolution
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Reverse Address Resolution
• The process of finding out the IP address of a host given a hardware address is called
Reverse Address ResolutionReverse Address Resolution
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ARP
• The Address Resolution Protocol is used by a sending host when it knows the IP address of the destination but needs the Ethernet address.
• ARP is a broadcast protocol - every host on the network receives the request.
• Each host checks the request against it’s IP address - the right one responds.
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ARP (cont.)
• ARP does not need to be done every time an IP datagram is sent - hosts remember the hardware addresses of each other.
• Part of the ARP protocol specifies that the receiving host should also remember the IP and hardware addresses of the sending host.
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ARP
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Services provided by IP
• Connectionless Delivery (each datagram is treated individually).
• Unreliable (delivery is not guaranteed).
• Fragmentation / Reassembly
• Routing.