Review of Important Networking Concepts. Recall the Example from last lecture

Transcription

1 Review of Important ing Concepts Review: ed communication architecture The TCP/IP protocol suite Jörg Liebeherr, 1998, Recall the Example from last lecture Ellington.cs.virginia.edu establishes an FTP connection to neon.cs.virginia: ftp neon.cs.virginia.edu ellington Local Campus neon We will use the example to illustrate some important networking concepts Jörg Liebeherr, 1998,

2 The example: Passing a simple packet from is not on my local network. Therefore, I need to send the packet to my default gateway with is address on my local network. DNS: ARP: What What The is IP is the address the IP MAC address of Therefore, I can send the packet directly. of address ARP: neon.cs.virginia.edu? The of MAC ? address isof is 00:e0:f9:23:a8:20 ARP: What is the MAC ellington.cs. ARP: address The of MAC ? address of neon.cs.virginia.edu virginia.edu is 00:20:af:03:98:28 ( ) ( ) router137.cs. virginia.edu ( ) router71.cs. virginia.edu ( ) frame frame Jörg Liebeherr, 1998, Communications Architecture The complexity of the communication task is reduced by using multiple protocol layers: Each protocol is implemented independently Each protocol is responsible for a specific subtask Protocols are grouped in a hierarchy A structured set of protocols is called a communications architecture or protocol suite Jörg Liebeherr, 1998,

3 TCP/IP Protocol Suite In this course, we will be mostly concerned with the TCP/IP protocol suite The TCP/IP protocol suite is the main characteristic for the networks that we call the Internet The TCP/IP suite has four layers: Application, Transport,, and (Data) Link Application Transport (Data) Link telnet, ftp, TCP, UDP IP, ICMP, IGMP Device Drivers Computers (hosts) implement all four layers. Gateways (Routers ) only have the bottom two layers. Jörg Liebeherr, 1998, Functions of the s Data Link : Service: Reliable transfer of frames over a link Functions: Synchronization, error control, flow control : Service: Moves packets inside the network Functions: Routing, addressing, congestion control Transport : Service: Controls delivery of data between hosts Functions: Connection establishment/termination, error control, flow control Application : Service: Handles details of application programs Functions: Everything is application specific Jörg Liebeherr, 1998,

4 TCP/IP Suite and OSI Reference Model You know about the OSI Reference protocol The TCP/IP protocol stack does not define the lower layers of a complete protocol stack Application Transport (Data) Link TCP/IP Suite Application Presentation Session Transport (Data) Link Physical OSI Reference Model Jörg Liebeherr, 1998, More Information on s An entity of a particular layer can only communicate with: 1. a peer layer entity using a common protocol (Peer Protocol) 2. adjacent layers to provide services and to receive services N+1 N+1 N+1 Protocol N+1 layer N+1/N interface N N N Protocol N layer N/N-1 interface N-1 N-1 N-1 Protocol N-1 Jörg Liebeherr, 1998,

5 s in the Example FTP program TCP IP Frame is an Ethernet IP datagram Driver Open ftp session to neon FTP program Establish a connection to TCP Open TCP connection to IP datagram is a Send a datagram IP (which TCP Send segment IP contains datagram to to a Send IP datagram to IP connection request) Frame is an Send Ethernet datagram toethernet IP datagram Send Ethernet datagram Driver Driver to Driver ellington.cs. router71.cs. virginia.edu Send Ethernet virginia.edu frame to :e0:f9:23:a8:20 00:e0:f9:23:a8:20 router137.cs. neon.cs. Send Ethernet virginia.edu virginia.edu frame to :20:af:03:98:28 Jörg Liebeherr, 1998, Encapsulation As data is moving down the protocol stack, each protocol is adding layer-specific control information Application User data TCP Application Header User data IP TCP segment Ethernet Driver Ethernet Header IP datagram Ethernet Trailer Jörg Liebeherr, 1998,

6 Encapsulation in our Example Let us look in detail at the first between ellington and router71.cs. This is the output of tcpdump -exn host :32: :a0:24:71:e4:44 0:e0:f9:23:a8: : > : S :607835(0) win 8192 <mss 1460> (DF) c 9d bff 808f f b b e b4 b4b4 Jörg Liebeherr, 1998, Encapsulation 6 bytes destination address source address type 4 bytes CRC Jörg Liebeherr, 1998,

7 Encapsulation: 6 bytes 00:e0:f9:23:a8:20 0:a0:24:71:e4:44 0x bytes CRC Jörg Liebeherr, 1998, Encapsulation: 32 bits version (4 bits) header length TTL Time-to-Live (8 bits) Identification (16 bits) Type of Service/TOS (8 bits) Protocol (8 bits) flags (3 bits) Total Length (in bytes) (16 bits) Fragment Offset (13 bits) Header Checksum (16 bits) Source IP address (32 bits) Destination IP address (32 bits) Jörg Liebeherr, 1998,

8 Encapsulation: 32 bits 0x4 0x5 0x d x06 8bff Jörg Liebeherr, 1998, Encapsulation: 32 bits Source Port Number Destination Port Number Sequence number (32 bits) header length Acknowledgement number (32 bits) 0 Flags TCP checksum kind=2 length window size urgent pointer Max. segment size Option: maximum segment size Jörg Liebeherr, 1998,

9 Encapsulation: 32 bits x598e Jörg Liebeherr, 1998, Encapsulation: No Application Data in this frame Jörg Liebeherr, 1998,

10 Different Views of ing Different s of the protocol stack have a different view of the network. This is FTP s and TCP s view of the network. ellington.cs FTP program neon.cs FTP program TCP TCP IP Jörg Liebeherr, 1998, View of IP Protocol Jörg Liebeherr, 1998,

11 View of Hardware ellington Olsson Hall neon Gilmer Hall 100 Mbps Ethernet 10 Mbps router71 / router137 Ethernet 155 Mbps ATM 155 Mbps ATM 622 Mbps ATM Jörg Liebeherr, 1998,