Network Model: Understanding Layered Communication and Protocols - Prof. Ala I. Al-Fuqaha, Study notes of Computer Science

Download Network Model: Understanding Layered Communication and Protocols - Prof. Ala I. Al-Fuqaha and more Study notes Computer Science in PDF only on Docsity! Network Model Why a Layered Model? All People Seem To Need Data Processing Layers with Functions Packet Propagation Each router provides its services to support upper-layer functions. LAN Devices Repeater Copies bits from one network to another Does not look at any bits Allows the extension of a network beyond physical length limitations REPEATER Bridge/Switch Copies frames from one network to another Can operate selectively - does not copy all frames (must look at data-link headers). Extends the network beyond physical length limitations. BRIDGE Router Copies packets from one network to another. Makes decisions about what route a packet should take (looks at network headers). ROUTERR UTER Ethernet LAN Segmentation • Switches break collision domains. • Routers break collision domains as well as broadcast domains. Ethernet Multi-access (shared medium). Every Ethernet interface has a unique 48 bit address (a.k.a. hardware address). Example: C0:B3:44:17:21:17 The broadcast address is all 1’s. Addresses are assigned to vendors by a central authority. Introduction to IP, Addressing, DHCP, ARP Anatomy of an IP Packet Version IP header length (HLEN) Type-of-service Total length Identification Flags Fragment offset Time-to-live Protocol Header checksum Source address Destination address Options Padding Data IP Address as a 32-Bit Binary Number Private Addresses Dynamic Host Configuration Protocol Allows a host to obtain an IP address using a defined range of IP addresses on a DHCP server. As hosts come online, contact the DHCP server, and request an address. A default gateway is the IP address of the interface on the router that connects to the network segment on which the source host is located. Default Gateway Network Address Translation Unleashing the Power of NAT Overload eae ti Eee Cd 192.168.0.1 ol a od Dee CRA Coie Padres: -200.0.0.1 Port 23 200.0.0.1 Port 23 192.168.0.1 Cre TCu Dros DU ose l ely Scie Se Lcd 192.168.0.2 ate dS —— De Ear ec Destination of Packet: Py RR a es) Pee] 192.168.0.2 EtG Gag Ect Cd PEP BULA en ad De Cm ce TP Address © -149.10.10.5 Port 23 149.10.10.5 Port 23 Frye ed Here we see how the NAT Overload router deals with multiple packets from 3 different hosts on the private network. Notice that only the ee ee) Pee Cce re CU RUC Cle Virtual Local Area Networks (VLAN) 2 VLAN Communication Typical Deployment Networks TCP Overview Connection- oriented Byte-stream app writes bytes TCP sends segments app reads bytes Full duplex Flow control: keep sender from overrunning receiver Congestion control: keep sender from overrunning network Application process Write bytes TCP Send buffer Segment Segment Segment Transmit segments Application process Read bytes TCP Receive buffer ■ ■ ■ TCP Header Options (variable) Data Checksum SrcPort DstPort HdrLen 0 Flags UrgPtr AdvertisedWindow SequenceNum Acknowledgment 0 4 10 16 31 • Flags: SYN, FIN, RESET, PUSH, URG, ACK • Checksum: IP pseudo header + TCP header + data IP Fragmentation Payload IP Header Payload Payload Payload IP Header IP Header IP Header More Fragements is Set More Fragements is NOT Set DNS: Root name servers • contacted by local name server that can not resolve name • root name server: contacts authoritative name server if name mapping not known gets mapping returns mapping to local name server • ~ 13 root name servers worldwide Further information about the root name servers can be found at: http://netmon.grnet.gr/stathost/rootns/ DNS Queries recursive query: puts burden of name resolution on contacted name server heavy load? iterated query: contacted server replies with name of server to contact “I don’t know this name, but ask this server” requesting host Sun.lopsys.net Csy01.cs.wmich.edu root name server local name server dns.lopsys.net 1 2 3 4 5 6 authoritative name server dns.cs.wmich.edu intermediate name server dns.wmich.edu 7 8 iterated query