ilab Lab 1+2 The Basics / Static Routing ISO/OSI Layer Model - PowerPoint PPT Presentation

Lehrstuhl für Netzarchitekturen und Netzdienste Institut für Informatik Technische Universität München ilab Lab 1+2 The Basics / Static Routing

ISO/OSI Layer Model (1979-1983) Applications, e.g. HTTP, FTP, … 7 Application Layer Representation of data 6 Presentation Layer 5 Management of Sessions Session Layer 4 Transport, e.g. TCP, UDP, SCTP Transport Layer 3 Network Layer Routing, e.g. IP 2 Data Link Layer Transmission of frames 1 Physical layer, e.g. Ethernet Physical Layer Ilab: The basics / Static Routing 2

Internet Layer Model vs. ISO/OSI 7 Applications 4 Application Layer 6 http, ftp, telnet, smtp, pop, … 5 End-to-end data transport 3 Transport Layer 4 tcp, udp, sctp, … 2 Routing in the internet Internet Layer 3 IPv4, IPv6 2 Interface to the physical medium 1 Link Layer Ethernet, WLAN, Token Ring, FDDI, … 1 • Alternative name: TCP/IP protocol hierarchy • Adaptation of the abstract ISO/OSI layer model for the internet • ISO/OSI layers 5, 6, 7 and layers 1, 2 are aggregated x = Equivalent to ISO/OSI Ilab: The basics / Static Routing 3

Horizontal Communication 4 Application Application 3 TCP TCP 2 IP IP IP IP 1 Net 1 Net 1 Net 2 Net 2 Net 3 Net 3 Router Router Telephone, SDH / SONET WLAN modem (Hi-Speed Fibre) • Horizontal communication = logical communication between instances of the same protocol layer over an abstract medium • Only the lowest layer has a real (indirect) connection with the partner instance Ilab: The basics / Static Routing 4

Vertical Communication 4 Application Application 3 TCP TCP 2 IP IP IP IP 1 Net 1 Net 1 Net 2 Net 2 Net 3 Net 3 Router Router Telefone, SDH / SONET WLAN Modem (Hi-Speed Fiber) • Vertical communication = Instances of a protocol layer communicate with instances of protocol layers above or below. Ilab: The basics / Static Routing 5

Cooperation of Protocol Instances: PDUs  A service provides a Service Access Point (SAP) to the layer above it  Protocol Data Units (PDUs) are encapsulated  TCP/UDP adds process addressing (ports) to IP  TCP adds reliability to IP  IP routes data packets through the network to the destination 4 Data Application TCP-Header Data 3 Transport Layer bzw. UDP-Header Data 2 IP-Header TCP/UDP-Header Data Internet Layer 1 MAC/LLC-Header IP-Header TCP/UDP-Header Data Trailer Link Layer Ilab: The basics / Static Routing 6

Internet Architecture: Common Design Decisions  Hold no information (state) in nodes between sender of data and destination (e.g. no need for resynchronisation)  All information specific for the stream is stored only at the sender and the destination of data: End-to-end principle  Separation of packet forwarding from one hop to the next and the creation of routing tables  Routing vs. Forwarding Ilab: The basics / Static Routing 7

TCP/IP Protocol Family – Overview  „TCP/IP “ is used often as a synonym for a whole family of protocols  The TCP/IP family and the ISO/OSI layer model: Session Layer TCP UDP Transport Layer IGMP ICMP IP Network Layer ARP RARP Data Link Layer  ICMP and IGMP use IP like an application layer (ISO/OSI) protocol, but are assigned to the network layer (ISO/OSI)  Application layer (ISO/OSI) protocols are e.g. FTP, TELNET or SMTP Ilab: The basics / Static Routing 8

Properties of IP  Paket-switched  Connectionless datagram service  Unreliable transmission:  Datagramms may get lost  Datagramms may overtake each other  Datagramms may be forwarded ad infinitum (routing loop)  Transmission errors that could not be fixed by the layer 2 protocol used, normally cannot be fixed by IP, too  ICMP (Internet Control Message Protocol) is used for error notification  No flow control  Used in private and public networks  Private home networks  Coupling of subnetworks in enterprise networks  Public (wide area) networks (e.g. in the internet backbone)  Best effort, no quality of service (QoS) guaranteed Ilab: The basics / Static Routing 9

IPv4 Datagramm Layout Don ‘ t Fragment Congestion Control (Explicit Congestion Notification) Reserved More Fragments QoS Class DiffServ Codepoint ECN 0 DF MF Bit 0 3 7 15 31 Version Hdr.Len DiffServ Total Length Identifier Flags Fragment Offset IP-Header Time to Live Protocol Header Checksum Source Address Destination Address Options and Padding Data Ilab: The basics / Static Routing 10

Control of IP: ICMP  IP only provides (unreliable) paket transmission  When errors occur or for testing purposes ICMP (Internet Control Message Protocol) is used.  ICMP uses IP Router connection Router Router interrupted Router Destination Sender ICMP message  Message type, examples:  Echo Request / Reply : Echo Reply is requested (" ping ").  Timestamp Request / Reply : similar to Echo Request: a timestamp that holds the time of arrival (query) and time of sending (response) is added. Ilab: The basics / Static Routing 11

ICMP: Error messages  Destination unreachable: A data packet could not be delivered, e.g. because of an interrupted cable or a router failure.  Time to live exceeded: A data packet was dropped by a router because the packet ‘ s TTL exceeded.  Parameter problem: A data packet was discarded due to illegal values in its IP header.  Source quench: A overloaded communication system requests the sender to throttle transmission rate.  Redirect: A data packet should be sent over another router. Ilab: The basics / Static Routing 12

ICMP: Packet layout  Transmission of ICMP messages  ICMP messages are transmitted in IP Header IP-packets. ICMP Message [Protocol = 1]  ICMP messages have the value „1 “ in the protocol field of the IP header. Type Code Checksum Info  Format of ICMP messages  Type: the type of this message, e.g. Type = 3 means „Destination unreachable “ )  Code: more specific information, e.g. „Network not reachable “ )  Checksum: Checksum over the ICMP message  The content of the Info-Field depends on the Type of the ICMP message, e.g. timestamps Ilab: The basics / Static Routing 13

Layer 2 Adresses  MAC addresses (also referred to as “ physical address ” )  Specific for the network type, e.g. Ethernet, Bluetooth, ATM  Are not unique for all network types  Ethernet / WLAN 48 Bit long (z.B.: aa:bb:cc:dd:ee:ff )  Contains information about vendor and product  MAC addresses are not hierarchically issued, e.g.:  Device with MAC aa:bb:cc:dd:ee:ff is located in the US  Device with MAC aa:bb:cc:dd:ee:fe is located in Japan  When MAC addresses would be used for global addressing of devices, routing of packets would not scale as every router would need to know the route to every possible destination Ilab: The basics / Static Routing 14

Routing Inside the Internet  IP addresses are 32 bit long  this results in 2^32 possible host addresses  A naive approach would result in huge routing tables, a router would need to know all routes to all end systems  impossible  Better approach: Hierarchical Addressing  Use first n bit of the IP address for addressing the network  Use last 32 - n bit of the IP address for addressing the host inside the network  Effect:  A router only needs to know how to reach the hosts within the own network  For reaching hosts outside the own network, the router only needs to know the router that „cares “ for the destination network Ilab: The basics / Static Routing 15

IP Address Classes 0 1 2 4 8 16 24 31 0 Net-ID Node-ID 1. Class A: Nets with up to 16 million nodes (prefix: 1 bit/ net: 7 / host: 24) 1 0 Net-ID Node-ID 2. Class B: Nets with up to 65.536 nodes (2/ 14/ 16) 1 1 0 Net-ID Node-ID 3. Class C: Nets with up to 256 nodes (3/ 21/ 8) 1 1 1 0 Multicast Address 4. Class D: used for group communication (multicast) 1 1 1 1 0 Reserved for future use 5. Class E, unused, reserved for future use Ilab: The basics / Static Routing 16

Subnetworks  Purpose: Split the static Class A, B C networks into parts (subnets)  Use:  Makes large (Class A) networks manageable  Easier network administration  Separation of business units  …  Implemented with subnetwork masks  Bsp: 255.255.255.0 Ilab: The basics / Static Routing 17

IP Subnetwork Addresses  IP-Address (in this example: Class B , prefix 10, 2/14/16): Network Part Local Part Network Part Subnet Part Host Part  Subnetwork mask marks the bits that describe the network and the subnetwork. In the binary representation of the subnetwork mask this area is represented with a sequence of set bits („1 “ )  Example: IP-Addresse: 129. 13. 3. 64 Subnetmask: 255. 255. 255. 0 1111 1111 1111 1111 1111 1111 0000 0000 Network: 129. 13. Subnetwork: 3. Endsystem: 64  The network part can be derived from the address class.  If the subnetwork mask only covers the network part (e.g. 255.255.0.0), no subnetwork is specified. Ilab: The basics / Static Routing 18