Why we need to divide network?

Transcription

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) 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

2 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

3 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

4 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:

5 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

6 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

7 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) 65 Routing: Forward IP-Packets Initially, a router must refer to entries about networks or subnets that are directly connected to it. Each interface must be configured with an IP address and a mask. The initial source of addressing is a user who types it into a configuration file. 66

8 Routing: types of routes 67 static routes - manually defined by the system administrator as the next hop to a destination; useful for security and traffic reduction default routes - manually defined by the system administrator as the path to take when there is no known route to the destination dynamic routing - the router learns of paths to destinations by receiving periodic updates from other routers. Default route A default network must exist in a routing table. Default routes keep routing tables shorter. When an entry for a destination network does not exist in a routing table, the packet is sent to the default network. Because a router does not have complete knowledge about all destination networks, it can use a default network number to indicate the direction to take for unknown network numbers. Use the default network number when you need to locate a route, but have only partial information about the destination network. 68

9 Different routing protocols a router can use an IP routing protocol to accomplish routing through the implementation of a specific routing algorithm. Examples of IP routing protocols include: RIP - a distance-vector routing protocol IGRP - Cisco s distancevector routing protocol OSPF - a link-state routing protocol EIGRP - a balanced hybrid routing protocol. 69 Routing: RIP RIP was originally specified in RFC Its key characteristics include the following: It is a distance-vector routing protocol. Hop count is used as the metric for path selection. The maximum allowable hop count is 15. By default, routing updates are broadcast every 30 seconds 70

10 Routing Table 71 The show ip route command displays the contents of the IP routing table, which contains entries for all known networks and subnetworks, along with a code that indicates how that information was learned. 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) 72

11 Train Network Structure 73 Sources: IEC WTB Data-Frame 74

12 Routing in a train The network layer routes packets from an Origin station to a Final station. To this effect, the network layer uses the mapping provided by several directories: a) the station directory, b) the function directory, c) the group directory, and d) the node directory. The network layer is connectionless. 75 Network-Layer / Routing 76

13 Routing Situations 77 Frame Structure 78

14 Frame Structure 79 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) 80