Introduction Layer 3. IP-Header: and RFC-760 Addressing schemes Subnetting Routing. Layer 3 Solution in Trains

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1 Chapter 2.3 Layer 3 Network Layer 1 Content Introduction Layer 3 IP Protocol IP-Header: and RFC-760 Addressing schemes Subnetting Routing Layer 3 Solution in Trains Communication Matrix (Information Based Communication) 2

Protocol aspect of the OSI-Model Endsystem 1 7 6 5 4 3 2 1 Layer 7 protocol Layer 6 protocol Transitsystem 3 2 1 transmission-system Endsystem 2 Protocols

2 Protocol aspect of the OSI-Model Endsystem Layer 7 protocol Layer 6 protocol Transitsystem transmission-system Endsystem 2 Protocols are defined between the same layers of two systems. They define rules and formats of message/information exchange Why network layer (1)? 4

3 Why network layer (2)? Locomotive Redundant nodes C Display Dezentrale I/O Main Control Dezentrale dez. I/O I/O Doors Türen Wagon: Single node Brake control Multimedia Hilfs- betriebe- Umrichter Dezentrale I/O Climate control Dezentrale I/O Vehicle bus WTB trainbus (UIC 556) Standard! MVB vehicle bus Climate Control Multimedia Hilfs- betriebe- Umrichter Vehicle Bus (CAN, FIP,...) Dezentrale I/O Trainset: Multiple Wagons Brake Control Dezentrale I/O Gateway WTB/MVB Doors Türen Main Control Antriebssteuerung Antriebssteuerung Dezentrale dez. I/O I/O Display C Dezentrale I/O Control-Wagon reduntand Nodes 5 MMI Subsystemes Motorr ONIX Umrichter Subsysteme Subsysteme, Motor Subsysteme, Motor Subsysteme ONIX Umrichter Subsysteme, motor MMI Why network layer (3)? 6

4 Network-Layer The Network Layer... segment network and control flow of traffic. provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks transfers packets from one network to another maintains the quality of service requested by the Transport layer. performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors. Is based on an logical addressing scheme Internet Protocol (IP) is the best known layer 3 protocol connectionless transfer of data fragmenting data into sufficiently small packets that the Layer 2 can accept it 7 Network segmentation Control network traffics and reduce broadcast traffics. Separate computer networks are managed by a single administration - Autonomous systems. 8

5 Communication among networks Networks operate in much the same manner. 9 Router Routers connect separate networks. Routers make best path decisions based on Layer 3 information. Routers actually switch packets from incoming ports to appropriate outgoing ports. Routers can change the media and Layer 2 behaviour 10

6 Data relaying 11 Path determination Path determination is the process that the router uses to choose the next hop in the path for the packet to travel to its destination based on the link bandwidth, hop, delay... 12

7 Network layer addressing Network address + Host address: Hierarchical Addressing Schemes. 13 Flat Addressing Scheme A 1 A 1 2 A 2 3 A 3 1 A 2 A 3 A 4 B 5 B 6 B B

8 MAC Addressing (Layer 2) 15 Hierarchical Addressing Scheme A1 A2 A3 A 1 A 1 B 2 A 2 3 A 3 A Local B Switch to B B1 B2 B3 16

9 Hierarchical Addressing Scheme Domestic Switch International Gateway Local Switch Network address The network address helps the router identify a path within the network cloud. The router uses the network address to identify the destination network of a packet within an internetwork. Network address is assigned by higher-level administrator. Host address is assigned manually or automatically by manager of that network. 18

Content Introduction Layer 3 IP Protocol IP-Header: www.ietf.

10 Content Introduction Layer 3 IP Protocol IP-Header: and RFC-760 Addressing schemes Subnetting Routing Layer 3 Solution in Trains Communication Matrix (Information Based Communication) 19 Network layer datagram At the network layer, the data is encapsulated within packets (also known as datagrams). Packet includes header - addressing and other control information - and actual data - whatever is passed down from the higher layers. 20

11 IP header format 21 IP header format: Version 4 bits. Indicates the version of of IP IP currently used. IPv4 :: 0100 IPv6 ::

12 IP header format: Header length 4 bits. IP IP header length : Indicates the datagram header length in in 32 bit words (4 (4 bits), and thus points to to the beginning of of the data. 23 IP header format: Service type 8 bits. Specifies the level of of importance that has been assigned by a particular upper-layer protocol. Precedence. Reliability. Speed. 24

13 IP header format: Total length 16 bits. Specifies the length of of the entire IP IP packet, including data and header, in in bytes. 25 IP header format: Identification 16 bits. Identification contains an integer that identifies the current datagram. Assigned by the sender to to aid in in assembling the fragments of of a datagram. 26

14 IP header format: Flags 3 bits. The second bit specifying whether the packet can be fragmented.. The last bit specifying whether the packet is is the last fragment in in a series of of fragmented packets. 27 IP header format: Fragment offset 13 bits. The field that is is used to to help piece together datagram fragments. The fragment offset is is measured in in units of of 8 octets (64 bits). The first fragment has offset zero. 28

15 IP header format: Time to Live 29 8 bits. Time-to-Live maintains a counter that gradually decreases to to zero, at at which point the datagram is is discarded, keeping the packets from looping endlessly. IP header format: Protocol 8 bits. Indicates which upper-layer protocol receives incoming packets after IP IP processing has been completed :: TCP TCP :: UDP UDP 30

16 IP header format: Header checksum 16 bits. A checksum on the header only, helps ensure IP IP header integrity. 31 IP header format: Addresses 32 bits each. Source IP IP Address Destination IP IP Address 32

17 IP header format: Options Variable length. Allows IP IP to to support various options, such as security, route, error report IP header format: Padding The header padding is is used to to ensure that the internet header ends on a 32 bit boundary. 34

18 Content Introduction Layer 3 IP Protocol IP-Header: and RFC-760 Addressing Schemes Subnetting Routing Layer 3 Solution in Trains Communication Matrix (Information Based Communication) 35 IP network address Network layer addresses are 32 bits long. The are presented as four octets in dotted decimal format. The IP address has two components: Network ID and Host ID. 36

19 Network ID and host ID Network ID : Assigned by Internet Network Information Center. Assigned by upper organization. Identifies the network to which a devices is attached. Host ID : Assigned by a network administrator. Identifies the specific device on that network. 37 Bits on the IP address Network Bits : Identifies network ID Identifies class of the IP address All of bits are 0: not allowed Host Bits : Identifies host ID All of bits are 0: reserved for network address All of bits are 1: reserved for broadcast address 38

20 IP address classes Different class addresses reserve different amounts of bits for the Network and Host portions of the address Provide the flexibility required to support different size networks 39 IP address classes: Class A 40

21 IP address classes: Class A The first bit of a Class A address is always 0. The first 8 bits to identify the network part of the address. Possible network address from to The remaining three octets can be used for the host portion of the address. Each class A network have up to 16,777,214 possible IP addresses. 41 IP address classes: Class B 42

22 IP address classes: Class B The first 2 bits of a Class B address is always 10. The first two octets to identify the network part of the address. Possible network address from to The remaining two octets can be used for the host portion of the address. Class B network have up to possible IP addresses. 43 IP address classes: Class C 44

23 IP address classes: Class C The first 3 bits of a Class C address is always 110. The first three octets to identify the network part of the address. Possible network address from to The remaining last octet can be used for the host portion of the address. Class C network have up to 254 possible IP addresses. 45 IP address classes: Summary : Class A : Loopback network : Class B : Class C < : Class D, multicast. >= : Class E, reserved. 46

24 Network address Network address provide a convenient way to refer to all of the addresses on a particular network or subnetwork. Two hosts with differing network address require a device, typically a router, in order to communicate. An IP address that ends with binary 0s in all host bits is reserved for the network address. 47 Broadcast address Broadcast goes to every host with a particular network ID number. An IP address that ends with binary 1s in all host bits is reserved for the directed broadcast address. An IP address with binary 1s in all network bits and host bits is reserved for the local broadcast address. 48

25 Local broadcast address STOP 49 Directed broadcast address Broadcast address

26 Example: is Class B address Network portion: Host portion: Network address: Broadcast address: Private addresses According to RFC Organizations make use of the private Internet address space for hosts that require IP connectivity within their enterprise network, but do not require external connections to the global Internet. Class A: Class B: Class C:

27 Content Introduction Layer 3 IP Protocol IP-Header: and RFC-760 Addressing Schemes Subnetting Routing Layer 3 Solution in Trains Communication Matrix (Information Based Communication) 53 Why we need to divide network? Network administrators sometimes need to divide networks, especially large ones, into smaller networks: Reduce the size of a broadcast domain. Improve network security. Implement the hierarchical managements. So we need more network addresses for your network. But I want the outside networks see our network as a single network. 54

Divide network by three 55 Subnetting Subnetworks are smaller divisions of network. Subnet addresses include the Class A, Class B, or Class C network portion, plus a subnet field and a host field.

28 Divide network by three 55 Subnetting Subnetworks are smaller divisions of network. Subnet addresses include the Class A, Class B, or Class C network portion, plus a subnet field and a host field. To create a subnet address, a network administrator borrows bits from the original host portion and designates them as the subnet field. Subnet addresses are assigned locally, usually by a network administrator. 56

and which part is the host field. 32 bits long.

29 Subnetting 57 Subnet mask Extended Network Prefix. Determines which part of an IP address is the network field and which part is the host field. 32 bits long. Divided into four octets. Network and Subnet portions all 1 s. Host portions all 0 s. 58

30 Default subnet mask: Example / Class C network: 24 bits for network portion. 0 bits for subnet portion. 8 bits for host portion. Subnet address: Subnet mask: Example / Class B network: 16 bits for network portion. 4 bits for subnet portion. 12 bits for host portion. Subnet address:

31 How many bits can I borrow? All of subnet bits are: 0 : reserved for network address. 1 : reserved for broadcast address. The minimum bits you can borrow is: 2 bits. The maximum bits you can borrow is: A: 22 bits ~ = subnets. B: 14 bits ~ = subnets. C: 06 bits ~ = 62 subnets. 61 Why we need to know Boolean ops? IP Address AND Subnet Mask Network layer performs the Boolean operations in order to find the network ID of a subnet Example: AND Network address: = Network and Subnet address 62

flooded broadcasts. Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router.

32 APR to find a MAC Address 63 Address all nodes (braodcast) Broadcasting messages are intended to be seen by every host on a network. The broadcast address is formed by using all 1s within a portion of the IP address Two kinds of broadcasts - directed broadcasts and flooded broadcasts. Broadcasts directed into a specific network/subnet are allowed and are forwarded by the router. These directed broadcasts contain all 1s in the host portion of the address. Flooded broadcasts ( ) are not propagated, but are considered local broadcasts. 64

Why we need to divide network?

Why we need to divide network? Content Introduction Layer 3 IP Protocol IP-Header: www.ietf.org and RFC-760 Addressing Schemes Subnetting Routing Layer 3 Solution in Trains Communication Matrix (Information Based Communication) 53 Why