RSC Part II: Network Layer 3. IP addressing Redes y Servicios de Comunicaciones Universidad Carlos III de Madrid These slides are, mainly, part of the companion slides to the book “Computer Networking: A Top Down Approach” generously made available by their authors (see copyright below). The slides have been adapted, where required, to the teaching needs of the subject above. All material copyright J.F Kurose and K.W. Ross, All Rights Reserved Computer Networking: A Top Down Approach 5 th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009.

Network LayerII-2 RSC Part II: Network Layer r II. 1 Basic Network layer concepts r II.2 Introduction to IP m Datagram format m ICMP r II.3 IP addressing r II.4 IP in operation m ARP r II.5 Network routing m Link state m Distance Vector m Hierarchical routing r II.6 Routing in the Internet m RIP m OSPF m BGP m Broadcast and multicast

Network LayerII-3 IP Addressing: introduction r IP address: 32-bit identifier for host, router interface 2 32 : hosts 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 LayerII-4 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 LayerII-5 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 LayerII-6 Subnets How many?

Network LayerII-7 IP addressing: CIDR CIDR: Classless InterDomain Routing m network portion of address of arbitrary length m address format: a.b.c.d/x, where x is number of bits in the network portion of the address Network part (network prefix) host part /23

Network LayerII-8 IP addresses: how to get one? Q: How does a host get IP address? r hard-coded by system admin in a file m Windows: control-panel->network->configuration- >tcp/ip->properties m UNIX: /etc/rc.config r DHCP: Dynamic Host Configuration Protocol: dynamically get address from as server m “plug-and-play”

Network LayerII-9 IP addresses: how to get one? Q: How does organization get prefix 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

Subnetting r A little bit more complex, Variable length subnet mask: / / / XXXXXXXXXX network subnet host Subnet mask: or /25 -> 126 interfaces 2 bits 8 bits 22 bits / / / / XXXXXXXX network subnet host 3 bits 7 bits 22 bits Subnet mask: or /24 -> 254 interfaces XXXXXXXXXX network subnet host 2 bits 8 bits 22 bits Subnet mask: or /24: /24, /24 y /24

Subnetting Network LayerII-11 r Special values: m All 0’s in host part Subnet m All 1’s in host part Broadcast address (2 h -2) possible interfaces in a subnet m Default m /8, /32 Loopback m /4 Multicast XXXXXXXXXXXXXXXX XXXXX XXX network subnet host s bits h bits XXXXXXXXXXXXXXXX XXXXX XXX network subnet host s bits h bits

Network LayerII-12 Forwarding Network Mask Gateway Interface Internet

Network LayerII-13 Hierarchical addressing: route aggregation “Send me anything with addresses beginning /20” / / /23 Fly-By-Night-ISP Organization 0 Organization 7 Internet Organization 1 ISPs-R-Us “Send me anything with addresses beginning /16” /23 Organization Hierarchical addressing allows efficient advertisement of routing information:

Network LayerII-14 Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 “Send me anything with addresses beginning /20” / / /23 Fly-By-Night-ISP Organization 0 Organization 7 Internet Organization 1 ISPs-R-Us “Send me anything with addresses beginning /16 or /23” /23 Organization

Network LayerII-15 IP addressing: the last word... Q: How does an ISP get block of addresses? A: The Internet Assigned Numbers Authority (IANA), operated by the ICANN (Internet Corporation for Assigned Names and Numbers), delegates to RIRs (Regional Internet Registry) m Address allocations m …

Network LayerII-16 Classful addressing r Disadvantages: m Too rigid: Class B too large for most organizations (65634 hosts), class C too small (254 hosts) m Either poor space address utilization or multiple entries in routing tables -> solution CIDR m Interesting for historical reasons m /4 still are multicast addresses Host Host HostNet Net Net Multicast addresses Reserved Class A Class B Class C Class D Class E X.Y.Z X.Y.Z X.Y.Z X.Y.Z

Network LayerII-17 Addresses and names r For humans, it is convenient to manage names instead of numbers m We can associate a name to an address: Eg it002.lab.it.uc3m.es m A distributed application: Domain Name System (DNS), resolves names into addresses DNS names are hierarchical to distribute their management m Nodes connected to the network need the address of a DNS server to resolve names Manual configuration or DHCP r This is the idea, DNS is a complex application that will be studied in future courses