Network Layer4-1 Chapter 4: Network Layer r 4. 1 Introduction r 4.2 Virtual circuit and datagram networks r 4.3 What’s inside a router r 4.4 IP: Internet Protocol m Datagram format m IPv4 addressing m ICMP m IPv6 r 4.5 Routing algorithms m Link state m Distance Vector m Hierarchical routing r 4.6 Routing in the Internet m RIP m OSPF m BGP r 4.7 Broadcast and multicast routing

Network Layer4-2 IP Addresses

Network Layer4-3 Special IP addresses r The IP address m Is used by hosts when they are booting r IP addresses with 0 as network number m Refer to the current network

Network Layer4-4 Class A, B, and C networks: default masks without subnetting r Routers use a default mask m To define size of the network and host parts of address r Default mask m is a 32 bit binary number written in dotted- decimal m defines the structure of an IP address Identifying the size of the network part of an IP address –Class A mask has a default mask of –Class B default mask => –Class C default mask =>

Network Layer4-5 A typical campus network A B C D E F G H

Network Layer4-6 Subnets r Main objective m Allow networks to be split into several parts (subnets) For internal use and still act like a single network to outside r Idea m Some bits are taken away from the host number To create a subnet number m A third part appears in the middle of the address

Network Layer4-7 Subnets: example r The main router uses a subnet mask m Indicating the split between network + subnet and host m The subnet mask in this case is alternative notation is /22 indicating a 22 bit long mask m Outside the network, subnetting is not visible

Network Layer4-8 How IP packets are processed at a router r Without subnetting m Each router has a routing table listing Some number of network IP addresses –Telling how to get to distant networks Some number of local host IP addresses –Telling how to get to local hosts r With subnetting m Router table is reduced furthermore By creating a three-level hierarchy (network, subnet, and host) m A router on subnet k Knows how to get to all other subnets and to local hosts does not have to know details about hosts on other subnets

Network Layer4-9 Scaling the IP address for the Internet r In the early 1990s m It became apparent that Internet was growing so fast That all IP addresses would be assigned by mid-1990s –new organizations would be unable to connect to Internet r Several solutions were developed m That allowed the Internet to grow Without letting us run out of IP addresses –Classless Interdomain Routing (CIDR) –Network Address Translation (NAT)

Network Layer4-10 IP Addressing r IP address: 32-bit identifier for host, router interface r interface: connection between host/router and physical link m router’s typically have multiple interfaces m host typically has one interface m IP addresses associated with each interface =

Network Layer4-11 Subnets r IP address: m subnet part (high order bits) m host part (low order bits) r What’s a subnet ? m device interfaces with same subnet part of IP address m can physically reach each other without intervening router network consisting of 3 subnets subnet

Network Layer4-12 Subnets / / /24 Recipe r To determine the subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet. Subnet mask: /24

Network Layer4-13 Subnets How many?

Network Layer4-14 IP addressing: CIDR CIDR: Classless InterDomain Routing m subnet portion of address of arbitrary length m address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet part host part /23

Network Layer4-15 Exercises r You have a class C network, and you need to design it for 7 usable subnets with each subnet handling a minimum of 18 hosts each. Which of the following network masks should you use? m m m m m None of the above

Network Layer4-16 Exercises r If a host on a network has the address /22, what is the address of the subnetwork to which the host belongs? m m m m m

Network Layer4-17 IP Addressing r IP address: 32-bit identifier for host, router interface r interface: connection between host/router and physical link m router’s typically have multiple interfaces m host typically has one interface m IP addresses associated with each interface =

Network Layer4-18 Subnets r IP address: m subnet part (high order bits) m host part (low order bits) r What’s a subnet ? m device interfaces with same subnet part of IP address m can physically reach each other without intervening router network consisting of 3 subnets subnet

Network Layer4-19 Subnets / / /24 Recipe r To determine the subnets, detach each interface from its host or router, creating islands of isolated networks. Each isolated network is called a subnet. Subnet mask: /24

Network Layer4-20 IP addressing: CIDR CIDR: Classless InterDomain Routing m subnet portion of address of arbitrary length m address format: a.b.c.d/x, where x is # bits in subnet portion of address subnet part host part /23

Network Layer4-21 IP addresses: how to get one? Q: How does network get subnet part of IP addr? A: gets allocated portion of its provider ISP’s address space ISP's block /20 Organization /23 Organization /23 Organization /23... ….. …. …. Organization /23

Network Layer4-22 CDR – Classless InterDomain Routing A set of IP address assignments. 5-59

Network Layer4-23 CIDR (ctd) r Routing tables: m AddressMask C: … E: … O: … ….. r A packet addressed to m Matches the Oxford base r A router m with a single line for all 3 universities => Three entries may be combined: /19