a.4. internetworking, lecture 1

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Introduction to internetworking

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Slide 1: 

Part A.4 Building scalable heterogeneous internets

Slide 2: 

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’

Slide 5: 

Source Internetworking example

Slide 6: 

Internetworking example Handling heterogeneity Routing Lookup based on Destination IP address

Slide 7: 

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).

Slide 8: 

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

Slide 17: 

Classful IP addresses

Slide 18: 

Classful IP addresses

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Classless (VLSM): Subnetting 202.125.138.0/24 202.125.138.0/25 202.125.138.128/25 Borrowing one host bit provides two subnetworks 202.125.138.0 – 202.125.138.255 202.125.138.0 – 202.125.138.127 202.125.138.128 – 202.125.138.255

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Subnetting 202.125.138.0/24 202.125.138.64/26 202.125.138.128/26 202.125.138.192/26 202.125.138.0/26 202.125.138.0 – 202.125.138.255 202.125.138.0 – 202.125.138.63 202.125.138.64 – 202.125.138.127 202.125.138.192 – 202.125.138.255 202.125.138.128 – 202.125.138.191 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) 202.125.138.0 /26 202.125.138.64 /26 202.125.138.128 /26 202.125.138.192 /26 202.125.138.0/26; 202.125.138.64/26; 202.125.138.128/26; 202.125.138.192/26 are directly connected to me 202.125.138.0/24 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) 192.4.16.0/20 . . 192.4.0.0/20 . . 192.4.0.0/14 . Contains 2 6 (20 bit: /20) prefixes including the two prefixes on RHS To only advertise the two /20 prefixes on RHS, use 192.4.0.0/19

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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 202.125.128.0/23 Islamabad LAN: 254 hosts Karachi LAN: 126 hosts

Slide 30: 

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 ]