a.4. internetworking, lecture 1

Category: Education

Presentation Description

Introduction to internetworking


Presentation Transcript

Slide 1:

Part A.4 Building scalable heterogeneous internets

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Application Transport Network Data Link Destination Host (Another LAN ) Bits Source Host Application Transport Network Data Link Bits Router (L3 Switch) Topic 3: Internetworking A router / L3 switch inspects destination IP to decide which port(s) to forward to The other LAN may speak/ understand another protocol (addressing/ framing/ MAC, etc.) Reca p

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No single networking technology is best for all needs The goal of internetworking is universal service across heterogeneous networks Motivations of Internetworking

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Logically a single network A communication system that supplies universal service allows arbitrary pairs of computers to communicate Motivations of Internetworking The need for ‘universal service’

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Source Internetworking example

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Internetworking example Handling heterogeneity Routing Lookup based on Destination IP address

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Internetworking example Handling heterogeneity Add a new MAC header conforming to the protocol supported between R1 and the next-hop (decided by the routing protocol).

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Fragmentation and Reassembly Internetworking example Issues relating to heterogeneity

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Internet Protocol (IP) Protocol of ‘the Internet’

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IP takes datagram approach Forwarding table at Switch 2

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IP Packet Format

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Fragmentation & Reassembly

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Fragmentation & Reassembly

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Classful / Classless IP addressing / 27 /26 / 25 / 28 /28 / 24 Internet Protocol (IP) Protocol of ‘the Internet’

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Internet Protocol IP Version 4; Address: 32 bits IP Version 6; Address: 128 bits Hierarchical addressing 2 parts: network , host determined by subnet mask 4,294,967,296 possible addresses = 2 32

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Classful IP addresses

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Classful IP addresses

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Classful IP addresses

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Classless (VLSM): Subnetting Borrowing one host bit provides two subnetworks – – –

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Subnetting – – – – – Borrowing two host bits provide four subnetworks

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Subnetting – General Definition Generalizing – for a network with m possible hosts, borrowing n bits provide 2 n subnetworks of m/n hosts

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Subnetting - Example

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CIDR uses both subnetting and supernetting Subnetting – efficient usage of IP addresses Supernetting – allows more efficient routing /24 /25 /25 Subnetting Supernetting /24 CIDR (Classless Interdomain Routing) /24 network

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Supernet (Route aggregation) /26 /26 /26 /26;;; are directly connected to me is directly connected to me Supernetting helps reduce the size of routing tables routers have to store

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CIDR (Classless Interdomain Routing) . . . . . Contains 2 6 (20 bit: /20) prefixes including the two prefixes on RHS To only advertise the two /20 prefixes on RHS, use

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Growth of Routing Table Projected growth of routing table before CIDR Longer prefixes being announced …then filtered But still the routing table grows CIDR worked for a while Source: http://potaroo.net

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http://www.subnet-calculator.com/cidr.php CIDR (Classless Interdomain Routing)

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Sidenote : How to get IP addresses? RIRs

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Exercise: Subnetting exercise Make a complete IP addressing plan for the network below assuming that you own IP block Islamabad LAN: 254 hosts Karachi LAN: 126 hosts

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Next lecture: Routing algorithms

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Chapter 4 : Internetworking [ P&D ] Section 4.1.1 to 4.1.4 Chapter 4 : The Network Layer [ K&R ] Section 4.4 (in particular) References

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[ End of lecture ]

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