TCPIPRefresher

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,TCP/IP Refresher,Prabhaker Mateti,(ack: Many many sources ),1,TCP/IP ?,TCP = Transmission Control Protocol,IP = Internet Protocol,Almost always includes other protocols:,UDP, User (Unreliable) Datagram,ICMP, Internet Control Message,ARP, Address Resolution,2,Whats a Protocol?,An agreed upon convention for communication.,Protocols must be formally defined and unambiguous,3,Layers,The relative heights indicate the level of functionality.,4,Unix is a Layered System,Applications,Libraries,System Calls,Kernel,5,Layers,The routines/methods of Layer N will,not,call Layer N+1.,The routines/methods of Layer N typically do call the same layer methods.,The routines/methods of Layer N typically do call Layer N-1 methods.,6,DoD model: Four Layers,Network Access Layer: Delivery over physical media in use.,Internet Layer: Delivery across different physical networks that connect source and destination machines.,Host-to-Host Layer: Connection rendezvous, flow control, retransmission of lost data, etc. TCP and UDP protocols are in this layer.,Process Layer: User-level functions, such as SMTP, rlogin.,7,OSI Reference Model,Seven Layers,7. Application,6. Presentation,5. Session,4. Transport,3. Network,2. Data Link,1. Physical,8,TCP/IP & OSI,In OSI reference model terminology -the TCP/IP protocol suite covers the network and transport layers.,TCP/IP can be used on many data-link layers (can support many network hardware implementations).,9,TCP,UDP,IP,802.3,Process Layer,Transport Layer,Network Layer,Data-Link Layer,Process,Process,ICMP, ARP,&,RARP,10,Physical Layer,Responsibility:,transmission of raw bits over a communication channel.,Issues:,mechanical and electrical interfaces,time per bit,distances,11,Data Link Layer - Data Link Control,Responsibility:,provide an error-free communication link,Issues:,framing (dividing data into chunks),header & trailer bits,addressing,10110110101,10110000001,12,The Data Link Layer - The MAC sub layer,Medium Access Control (MAC) - needed by multi-access networks.,MAC provides DLC with “virtual wires” on multi-access networks.,13,Ethernet: A Data-Link Layer,IEEE 802.3,Variety of physical layers.,Multi-access (shared medium).,Interface has a unique 6-byte hardware address. (E.g. 00-D0-09-E8-08-61),The broadcast address is all 1s.,Addresses are assigned to vendors by a central authority.,14,An Ethernet Frame,Preamble is a sequence of alternating 1s and 0s used for synchronization.,CRC is Cyclic Redundancy Check,8 bytes,6,6,2,0-1500,4,Preamble,Destination,Address,Source,Address,Len,CRC,DATA,15,Ethernet Addressing,Each NIC looks at every,frame,and inspects the destination address. If the address does not match the hardware address of the interface or the broadcast address, the frame is discarded.,Some NICs can be programmed to recognize multicast addresses.,16,The Network Layer,Responsibilities:,path selection between systems (routing).,subnet flow control.,fragmentation & reassembly,translation between different network types.,Issues:,packet headers,virtual circuits,17,The Transport Layer,Responsibilities:,provides virtual end-to-end links between peer processes.,end-to-end flow control,Issues:,headers,error detection,reliable communication,18,The Session Layer,Responsibilities:,establishes, manages, and terminates sessions between applications.,service location lookup,Many protocol suites do not include a session layer.,19,The Presentation Layer,Responsibilities:,data encryption,data compression,data conversion,Many protocol suites do not include a Presentation Layer.,20,The Application Layer,Responsibilities:,anything not provided by any of the other layers,Issues:,application level protocols,appropriate selection of “type of service”,21,Layering & Headers,Each layer needs to add control information.,Typically prefixed to the data before passing on to the lower layer.,22,Headers,Process,Transport,Network,Data Link,Process,Transport,Network,Data Link,DATA,DATA,DATA,DATA,H,H,H,H,H,H,23,Example Headers,Physical: no header,Data Link:,address of the receiving endpoints,address of the sending endpoint,length of the data,checksum,24,Network layer header - examples,protocol suite version,type of service,length of the data,packet identifier,fragment number,time to live,protocol,header checksum,source network address,destination network address,25,Connecting Networks,Repeater: physical layer,Bridge: data link layer,Router: network layer,Gateway: network layer and above.,26,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,27,Bridge,Copies frames from one network to another,Can operate selectively - does not copy all frames (looks at data-link headers).,Extends the network beyond physical length limitations.,BRIDGE,28,Router,Copies packets from one network to another.,Makes decisions about what route a packet should take (looks at network headers).,ROUTER,29,Gateway,Operates as a router,Data conversions above the network layer.,Conversions:,encapsulation - use an intermediate network,translation - connect different application protocols,encryption - could be done by a gateway,30,Encapsulation Example,Gateway,Gateway,Provides service connectivity even though intermediate network does not support protocols.,31,Translation,Translate from green protocol to brown protocol,Gateway,32,Encryption gateway,Secure,Network,Secure,Network,Encryption/Decryption,Gateways,GW,GW,?,?,?,Insecure,Network,33,Hardware v. Software,Repeaters are typically hardware devices.,Bridges can be implemented in hardware or software.,Routers and gateways are typically implemented in software so that they can be extended to handle new protocols.,Many workstations can operate as routers or gateways.,34,Modes of Service,connection-oriented vs. connectionless,sequencing,error-control,flow-control,byte stream vs. message based,full-duplex vs. half-duplex.,35,Connection-Oriented Service,establishment of a logical connection between two processes.,transfer data,terminate connection.,36,Connectionless Service,Sends independent messages.,37,Sequencing,Sequencing provides support for an order to communications.,A service that includes sequencing requires that messages (or bytes) are received in the same order they are sent.,38,Error Control,Some services require error detection.,Checksums provide a simple error detection mechanism.,Error control sometimes involves notification and retransmission.,39,Flow Control,Flow control prevents the sending process from overwhelming the receiving process.,Flow control can be handled in a variety of ways.,40,Byte Stream vs. Message,Byte stream implies an ordered sequence of bytes with no message boundaries.,Message oriented services provide communication service to chunks of data called,datagrams,.,41,Full- v. Half-Duplex,Full-Duplex services support the transfer of data in both directions.,Half-Duplex services support the transfer of data in one direction.,42,End-to-End v. Hop-to-Hop,Service modes, flow control and error control can be,Either between endpoints of the communication.,Or between consecutive nodes on the path between the endpoints.,43,End-to-End,Process A,Process B,44,Hop-by-Hop,Process A,Process B,45,Buffering,Buffering can provide more efficient communications.,Buffering is most useful for byte stream services.,Process A,Process B,Send,Buffer,Recv.,Buffer,46,Addresses,Physical Layer: no address necessary,Data Link Layer: address must be able to select any host on the network.,Network Layer: address must be able to provide information to enable routing.,Transport Layer: address must identify the destination process.,47,Broadcasts,Broadcast = sending a message from one host to all other hosts on the network.,A special address called the “broadcast address” is created.,Some popular network services are based on broadcasting (,YP/NIS, rup, rusers,),48,The IP in TCP/IP,IP is the network layer,packet delivery service (host-to-host).,translation between different data-link protocols.,49,IP Datagrams,IP provides connectionless, unreliable delivery of IP datagrams.,Connectionless: each datagram is independent of all others.,Unreliable: there is no guarantee that datagrams are delivered correctly or at all.,50,IP Addresses,The address must include information about what,network,the receiving host is on. This makes routing feasible.,IP addresses are not the same as the underlying data-link (MAC) addresses.,51,IP Addresses,Includes a network ID and a host ID.,A Network ID is assigned to an organization by a global authority ( ),Host IDs are assigned locally by a system administrator.,52,IP Addresses,A single NIC is assigned one IP address.,A host may have multiple NICs, and therefore multiple,host,addresses.,Hosts that share a network all have the same IP,network,address (the network ID).,53,Subnet Addresses,An organization can subdivide its host address space into groups called subnets.,The subnet ID is generally used to group hosts based on the physical network topology.,It is possible to have a single wire network with multiple subnets.,NetID,SubnetID,HostID,54,IP4 Addresses,Class,0,NetID,10,110,NetID,1110,Multicast Address,HostID,NetID,HostID,HostID,A,B,C,D,8 bits,8 bits,8 bits,8 bits,55,IP Addresses,An IP,broadcast,address has a host- ID of all 1s.,An IP address that has a host ID of all 0s is called a,network,address and refers to an entire network.,56,IP Addresses v. MAC Addresses,IP Addresses are not recognized by NIC.,The process of finding the MAC address of a host given the IP address is called,Address Resolution.,The process of finding out the IP address of a host given a hardware address is called,Reverse Address Resolution.,57,IPv6 addresses,Address is 128 bits long (16 bytes),Addresses are written in hexadecimal,Addresses can be abbreviated,3FFE:0B00:0000:0000:0000:0000:0000:0001,3FFE:0B00:0001,3FFE:B00:1,There is no broadcast addresses, only multicast.,Loopback address is :1,Addresses are scoped,Link-local, site-local, global,58,IP6 Address,16 bits,3FFE:,0B00:,1234:,0000:,0000:,0000:,0000:,0001,128 bits,59,IP4-Compatible IP6 Address,0000 . . . 0000,IP4 Address,0000,80 bits,32 bits,16 bits,80 bits of 0s followed by 16 bits of 0s, followed by a 32 bit IP4 Address:,60,ARP,ARP is a broadcast protocol. Each host checks the request against its own host addresses - the matched one responds.,Hosts remember the hardware addresses of others.,ARP protocol specifies that the receiving host should also remember the IP and hardware addresses of the sending host.,61,Services provided by IP,Connectionless Delivery (each datagram is treated individually).,Unreliable (delivery is not guaranteed).,Fragmentation / Reassembly (based on hardware MTU).,Routing.,Error detection.,62,IP Datagram,VERS,HL,Fragment Offset,Fragment Length,Service,Datagram ID,FLAG,TTL,Protocol,Header Checksum,Source IP Address,Destination IP Address,Options (if any),(TCP) Data,1 byte,1 byte,1 byte,1 byte,63,IP Datagram Fragmentation,Fragmentation can happen when datagrams are forwarded through a network for which they are too big.,IP specifies that datagram reassembly is done only at the destination (not on a hop-by-hop basis).,If any of the fragments are lost the entire datagram is discarded (and an ICMP message is sent to the sender).,64,ICMP (Internet Control Message Protocol),ping,ICMP uses IP to deliver messages.,ICMP messages are usually generated and processed by the IP layer, not the user process.,65,ICMP,If packets arrive too fast the receiver discards excessive packets and sends an ICMP message to the sender (SOURCE QUENCH).,If an error is found (header checksum problem, say) the packet is discarded and an ICMP message is sent to the sender.,66,ICMP Message Types,Echo Request,Echo Response,Destination Unreachable,Redirect,Time Exceeded,Redirect (route change),more .,67,UDP (User Datagram Protocol),UDP is a transport protocol,Uses IP to deliver datagrams,Connectionless, Unreliable, Minimal,UDP uses,ports,to provide communication services to individual processes.,68,Ports,Port,: an abstract destination point.,Ports are identified by a positive 16-bit integer.,Operating systems provide some mechanism that processes use to specify a port.,69,Ports,Host A,Host B,Process,Process,Process,Process,Process,Process,70,UDP Datagram Format,Source Port,Destination Port,Length,Checksum,Data,71,Sockets,72,Sockets,An,active socket,is connected to a remote active socket. Closing the connection destroys the active sockets at each endpoint.,A,passive socket,is not connected, but rather awaits an incoming connection, which will spawn a new active socket.,73,Sockets v. Ports,A socket is not a port. A socket is,associated,with a port. This is a many-to-one relationship.,Each port can have a single passive socket, awaiting incoming connections, and multiple active sockets, each corresponding to an open connection on the port.,74,TCP,Transmission Control Protocol :,Connection-oriented,Reliable,Full-duplex,Byte-Stream,75,Connection,Four Numbers: Source IP Address, Source Port, Destination IP Address, Destination Port,“connection is established”: Operating Systems of both source and destination hosts are maintaining “state information” re the connection.,76,Connection-Oriented,Connection oriented,means that a virtual connection is established before any payload data is transferred.,If the connection cannot be established the user program is notified.,If the connection is ever interrupted the user program is notified.,77,Connection establishment,Connection establishment phase is required,Ensures that the receiving process is available and to synchronize sequence numbers, etc.,78,TCP State Diagram,79,Reliable,Every transmission of data is acknowledged by the receiver.,If the sender does not receive ACK within a specified amount of time, the sender retransmits the data.,ACK can be piggybacked on data.,80,Byte Stream,Stream,means that the connection is treated as a stream of bytes.,The user application does not need to package data in individual datagrams (as with UDP).,81,Buffering,TCP is responsible for buffering data and determining when it is time to send a datagram.,It is possible for an application to tell TCP to send the data it has buffered without waiting for a buffer to fill up.,82,Full Duplex,TCP provides transport in both directions.,To the application program these appear as two unrelated data streams, although TCP can piggyback control and data communication by providing control information (such as an ACK) along with user data.,83,TCP Ports,Interprocess communication via TCP is achieved with the use of ports (just like UDP).,UDP ports have no relation to TCP ports (different name spaces).,84,TCP/UDP Ports,Reserved Ports less than 1024: Only root can bind to these ports.,Local Port of a process that requested the connection. Usually a random number, 0-65535.,Remote Port: What application accepted the connection. Usually a known number. /etc/services. E.g.,80 for HTTP,143 for IMAP,443 for HTTP/SSL,85,TCP Segments,The chunk of data that TCP asks IP to deliver is called a,TCP segment,.,Each segment contains:,data bytes from the byte stream,control information that identifies the data bytes,86,TCP Segment Format,Destination Port,Options (if any),Data,1 byte,1 byte,Source Port,Sequence Number,Request Number,1 byte,1 byte,offset,Res,Control,Window,Checksum,Urgent Pointer,87,Sequence Number,The “positional” number of the first data byte in this segment, except when SYN control flag is 1.,If SYN is 1 the sequence number is the initial sequence number (ISN).,32 bit unsigned integer,88,Sequence Number,Initial Sequence Number (ISN) is randomly generated.,What if ISN is not random?,You can hijack and kill arbitrary connections!,89,Acknowledgment Number,If the ACK control bit is set, this field contains the value of the next sequence number the sender of the segment is expecting to receive. Once a connection is established this is always included.,90,Control Bits,URG: Urgent Pointer field significant,PSH: Push Function,ACK: Acknowledgment field significant,RST: Reset the connection,SYN: Synchronize sequence numbers,FIN: No more data from sender,91,TCP v. UDP,Q: Which protocol is better ? A: It depends on the application.,TCP provides a connection-oriented, reliable byte stream service (lots of overhead).,UDP offers minimal datagram delivery service (as little overhead as possible).,92,TCP three-way handshake,Establishes a connection.,A:,“I would like to talk to you B.”,A sends a SYN packet to B,B:,“Ok, lets talk.”,B sends a SYN-ACK packet to A,A:,“Thanks for agreeing.”,A sends ACK to B,93,TCP three-way handshake,Flags src dst seq ack,SYN 1037 80,102723769,0,SYN-ACK 80 1037,1527857206,102723770,ACK 1037 80,102723770,1527857207,94,Four-Way Handshake,The Four-Way Handshake terminates a previously established connection:,A to B: FIN,B to A: ACK,B to A: FIN,A to B: ACK,95,Connection Resetting,Host X sends an RST packet resetting the connection if:,Y requested a connection to a non-existent port P on host X, or,For whatever reason (idle for a long time, or an abnormal condition, .), the host X (client or the sever) wishes to close the connection.,Resetting is unilateral.,96,