Introduction to Computer Networks CMPE 150 Fall 2005 Lecture 25 CMPE 150 Introduction to Computer Networks 1 Announcements Homework 4 due today by midnight No class on Friday 11 25 05 IMPORTANT No lab tonight Make up lab session next week Final exam December 7th 4 7pm In class Closed books notes Course evaluation Need volunteers CE 151 will be offered in Winter 06 CMPE 150 Introduction to Computer Networks 2 Today IP Cont d CMPE 150 Introduction to Computer Networks 3 IP Internet Protocol Glues Internet together Common network layer protocol spoken by all Internet participating networks Best effort datagram service No reliability guarantees No ordering guarantees CMPE 150 Introduction to Computer Networks 4 IP Versions IPv4 IP version 4 Current predominant version 32 bit long addresses IPv6 IP version 6 aka IPng Evolution of IPv4 Longer addresses 16 byte long CMPE 150 Introduction to Computer Networks 5 IP Datagram Format IP datagram consists of header and data or payload Header 20 byte fixed mandatory part Variable length optional part CMPE 150 Introduction to Computer Networks 6 The IP v4 Header CMPE 150 Introduction to Computer Networks 7 IP Options 5 54 CMPE 150 Introduction to Computer Networks 8 IP Addresses IP address formats CMPE 150 Introduction to Computer Networks 9 IP Addresses Cont d Class A 128 networks with 16M hosts each Class B 16 384 networks with 64K hosts each Class C 2M networks with 256 hosts each More than 500K networks connected to the Internet Network numbers centrally administered by ICANN CMPE 150 Introduction to Computer Networks 10 IP Addresses Cont d Special IP addresses CMPE 150 Introduction to Computer Networks 11 Scalability of IP Addresses Problem a single A B or C address refers to a single network As organizations grow what happens CMPE 150 Introduction to Computer Networks 12 Example A Campus Network CMPE 150 Introduction to Computer Networks 13 Solution Subnetting divide the organization s address space into multiple subnets How Use part of the host number bits as the subnet number Example Consider a university with 35 departments With a class B IP address use 6 bit subnet number and 10 bit host number This allows for up to 64 subnets each with 1024 hosts CMPE 150 Introduction to Computer Networks 14 Subnets A class B network subnetted into 64 subnets CMPE 150 Introduction to Computer Networks 15 Subnet Mask Indicates the split between network and subnet number host number Subnet Mask 255 255 252 0 or 22 network subnet part CMPE 150 Introduction to Computer Networks 16 Subnetting Observations Subnets are not visible to the outside world Thus subnetting and how is a decision made by local network admin CMPE 150 Introduction to Computer Networks 17 Subnet Example Subnet 1 10000010 00110010 000001 00 00000001 130 50 4 1 Subnet 2 10000010 00110010 000010 00 00000001 130 50 8 1 Subnet 3 10000010 00110010 000011 00 00000001 130 50 12 1 CMPE 150 Introduction to Computer Networks 18 Problem with IPv4 IPv4 is running out of addresses Problem class based addressing scheme Example Class B addresses allow 64K hosts More than half of Class B networks have fewer than 50 hosts CMPE 150 Introduction to Computer Networks 19 Solution CIDR CIDR Classless Inter Domain Routing RFC 1519 Allocate remaining addresses in variablesized blocks without considering classes Example if an organization needs 2000 addresses it gets 2048 address block Forwarding had to be modified Routing tables need an extra entry a 32 bit mask which is ANDed with the destination IP address If there is a match the packet is forwarded on that interface CMPE 150 Introduction to Computer Networks 20 Network Address Translation Another quick fix to the address shortage in IP v4 Specified in RFC 3022 Each organization gets a single or small number of IP addresses This is used for Internet traffic only For internal traffic each host gets its own internal IP address Three IP ranges have been declared as private 10 0 0 0 10 255 255 255 8 172 16 0 0 172 31 255 255 12 192 168 0 0 192 168 255 255 16 No private IP address can show up on the Internet i e outside the organization s network CMPE 150 Introduction to Computer Networks 21 NAT Network Address Translation CMPE 150 Introduction to Computer Networks 22 Internet Control Protocols Companion protocols to IP Control protocols used mainly for signaling and exchange of control information Examples ICMP ARP RARP BOOTP and DHCP CMPE 150 Introduction to Computer Networks 23 ICMP Internet Control Message Protocol A way to debug the Internet and find out what is happening at routers Defines a dozen different messages that are generated typically by routers upon some unexpected event CMPE 150 Introduction to Computer Networks 24 ICMP Message Types 5 61 CMPE 150 Introduction to Computer Networks 25 Address Resolution Protocol ARP RFC 826 Protocol for machines to map IP addresses to Ethernet addresses This is needed when packet needs to be delivered to a local host on a LAN Ethernet CMPE 150 Introduction to Computer Networks 26 ARP Example Host 1 wants to send packet to host 2 Assume that host 1 knows host 2 s IP address Host 1 builds packet with host 2 s IP address IP knows it s a local destination but now needs host 2 s Ethernet address CMPE 150 Introduction to Computer Networks 27 ARP Operation Host 1 broadcasts an ARP request on the Ethernet asking who owns host 2 s IP address Host 2 replies with its Ethernet address Some optimizations ARP caches Piggybacking host s own Ethernet address on ARP requests Proxy ARP services ARP requests for hosts on separate LANs CMPE 150 Introduction to Computer Networks 28 Beyond ARP ARP solves the problem of mapping IP address to Ethernet address How do we solve the inverse problem I e how to map an Ethernet address to an IP address Older protocols RARP RFC 903 and BOOTP RFC 951 RARP broadcasts not forwarded by routers BOOTP uses UDP but requires manual configuration of IP Ethernet mappings CMPE 150 Introduction to Computer Networks 29 DHCP Dynamic Host Configuration Protocol RFCs 2131 and 2132 Assigns IP addresses to hosts dynamically DHCP server may not be on the same LAN as requesting host DHCP relay agent CMPE 150 Introduction to Computer Networks 30 DHCP Operation Newly booted host broadcasts a DHCP DISCOVER message DHCP relay agent intercepts DHCP DISCOVERs on its LAN and unicasts them to DHCP server CMPE 150 Introduction to Computer Networks 31 DHCP Operation CMPE 150 Introduction to Computer Networks 32 DHCP
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