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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.