Internetworking Internetworking Address Resolution Protocol - PDF document

Internet Protocol Suite: Transport Internet Protocol Suite: Transport • TCP: Transmission Control Protocol • Byte stream transfer Internet Protocol Suite Internet Protocol Suite • Reliable, connection-oriented service • Point-to-point (one-to-one) service only Srinidhi Varadarajan • UDP: User Datagram Protocol • Unreliable (“best effort”) datagram service • Point-to-point, multicast (one-to-many), and • broadcast (one-to-all) Internet Protocol Suite: Network Internet Protocol Suite: Network Internet Protocol Suite: Data Link Internet Protocol Suite: Data Link z IP: Internet Protocol – Unreliable service z ARP: Address Resolution Protocol – Performs routing – Translates from an IP (network) address to a – Supported by routing protocols, network interface (hardware) address, e.g. IP • e.g. RIP, IS-IS, address-to-Ethernet address or IP address-to- • OSPF, IGP, and BGP FDDI address z ICMP: Internet Control Message Protocol – Used by IP (primarily) to exchange error and z RARP: Reverse Address Resolution control messages with other nodes Protocol z IGMP: Internet Group Management – Translates from a network interface (hardware) Protocol address to an IP (network) address – Used for controlling multicast (one-to-many transmission) for UDP datagrams Internetworking Internetworking Address Resolution Protocol Address Resolution Protocol z Motivation (ARP) (ARP) – Heterogeneity ARP Query – Scale What is the Ethernet Address of 130.245.20.2 Ethernet z IP is the glue that connects heterogeneous networks giving the illusion of a homogenous one. ARP Response IP Source IP Destination 0A:03:23:65:09:FB IP: 130.245.20.1 IP: 130.245.20.2 Ethernet: 0A:03:21:60:09:FA Ethernet: 0A:03:23:65:09:FB z Salient Features z Maps IP addresses to Ethernet Addresses – Best Effort Service Model – Global Addressing Scheme z ARP responses are cached Application Layer 1

Internet Protocol: IP Internet Protocol: IP Internet Protocol: IP Internet Protocol: IP z Two transport services are commonly z The Internet Protocol (IP) delivers built on top of IP datagrams across networks through – Transmission Control Protocol (TCP) routers – User Datagram Protocol (UDP) z IP provides unreliable datagram service – Other transport protocols may also use IP, e.g. – Datagrams (packets) may or may not be the Real Time Transport Protocol (RTP, RTSP) delivered z IP functions: – Datagrams may arrive at destination out of – Route datagrams through the Internet order – Provide Internet-wide addressing – Datagrams may be arbitrarily delayed – Fragment datagrams, as needed for underlying z Datagram service is not demanding on the network underlying network, thus allowing just z Currently version: IPv4. IPv6 is “next about any network to join the Internet generation” IP Global IP Addresses Global IP Addresses Internet Addressing Internet Addressing z Properties – globally unique z Example: IP address for abc.xyz.net – hierarchical: network – 10000000 10101101 01011100 01100000 7 24 + host A: 0 Network Host – 128.173.92.96 14 16 – netmask: 255.255.0.0 z Dot Notation B: 1 0 Network Host – network: 128.173.0.0 – 10.3.2.4 21 8 C: 1 1 0 Network Host – hostid: 92.96 – 128.96.33.81 – 192.12.69.77 Internet Addressing Internet Addressing IP Datagrams IP Datagrams z IP datagrams include z Special addresses used for broadcasting – Header, minimum size of 20 bytes – Directed broadcast: network (or subnet) plus – Data hostid that is all 1’s z Data size – Limited broadcast: all 1’s (network and hostid) – Less than or equal to minimum transport unit z Example: broadcasting for abc.xyz.net (MTU) of the underlying network – Directed broadcast (using subnet): z Fragmentation 128.173.255.255 – Packets may need to be fragmented at – Limited broadcast: 255.255.255.255 intermediate nodes if packet is too big for an z The Address Resolution Protocol (ARP) intermediate network provides a translation between an IP • Path MTU less than link MTU at sender address and an appropriate local network – Receiver reassembles fragments to form entire address (e.g. Ethernet physical address) IP packet Application Layer 2

IP Datagram Datagram Format Format IP IP Header Fields IP Header Fields 0 4 8 16 19 31 Version HLen TOS Length z Identification: unique datagram identifier Ident Flags Offset z Total Length: length of this datagram + header, in bytes TTL Protocol Checksum – Hosts are required to accept datagrams up to SourceAddr 576 bytes DestinationAddr – Many applications (e.g. NFS) accept up to Pad 8,192 bytes Options (variable) (variable) – Datagram may be fragmented Data z Internet Header Length: length of header in 32-bit words IP Header Fields IP Header Fields IP Header Fields IP Header Fields z Fragment Offset: offset of fragment in this z Protocol: identifies higher level protocol datagram in 8-byte units that provided data z Flags: indicate z Version: IP version identifier (currently 4) – If this is last fragment, and z Type of Service: – If datagram should not be fragmented – Precedence field (ignored) z Time To Live: maximum number of routers – Type of service (TOS) -- maximize throughput, through which the datagram may pass minimize delay, maximize reliability, minimize cost (no guarantees, though) – Decremented at each router z Header Checksum: checksum over header – Used to prevent looping in the network (protects addresses, lengths, etc.) – Also used to limit scope of multicast datagrams – 16-bit one’s complement sum IP Header Fields IP Header Fields z Source IP Address: full address of source node z Destination IP Address: full address of destination node z Options (rarely used, may not be supported by routers): – Security and handling restrictions – Record route – Loose source routing – Strict source routing Application Layer 3