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Basic Ethernet Principals Westermo Data Communications UK Ltd

Basic Ethernet Principals Westermo Data Communications UK Ltd. Objectives. Gain a basic understanding of Ethernet and IP with a focus on the first three layers of the OSI model.

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Basic Ethernet Principals Westermo Data Communications UK Ltd

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  1. Basic Ethernet Principals Westermo Data Communications UK Ltd

  2. Objectives Gain a basic understanding of Ethernet and IP with a focus on the first three layers of the OSI model. Be able to describe and configure a small network with an understanding of IP addresses and demonstrate knowledge of different types of network traffic

  3. What is Ethernet? • Shared communication medium • Address – based system • CSMA/CD • Fault tolerant • Protocol independent

  4. How does Ethernet work? Ethernet works on a fairly simple mechanism: CSMA/CD Carrier Sense, Multiple Access with collision detection B A C D

  5. 7 Layer OSI Model • Hierarchal model for defining communication between Ethernet devices. • Defines end-to-end communication between applications • Lower layers “encapsulate” data from higher layers

  6. Network TopologiesLAN WANLocal Area Network Wide Area Network

  7. Network TopologiesLAN WANLocal Area Network Wide Area Network

  8. Point to point (bus topology) Hub – Spoke (star topology) Ring / Mesh Network Topology

  9. Network Devices • Layer 1: • Hub / Bridge • Forwards all network traffic out of all ports • One collision domain • Simple (dumb) unit

  10. Network Devices • Layer 2: • Switch • Makes forwarding decisions based on source and destination MAC address • Builds a MAC address table to forward unicast packets • Breaks up collision domains • VLAN tagging support, and VLAN trunk support (802.1q)

  11. Network Devices • Layer 3: • Router • Makes forwarding decisions on source and destination IP Address’ • Routes data between different networks • Builds IP routing table to forward traffic between networks • Breaks up broadcast domains • Inter-VLAN routing • Firewall • Supports routing and redundancy protocols

  12. Ethernet Addressing • Layer 2 - MAC Address • 48 bit address written in HEX format • Physically hard-coded onto network adapter 00-22-FB-BB-AC-E8 OUI Organisation Unique Identifier NIC Network Interface Controller Used for local communication between devices

  13. IPv4 Addressing • Layer 3 - IP Address • 32 bit address written in “dotted decimal” • Logical addressing scheme • Uses a “Subnet Mask” to identify Network and Host portions of address 192 . 168 . 0 . 1 255 . 255 . 255 . 0

  14. IPv4 Addressing 32 Bits Network Portion Host Portion 8 Bits 8 Bits 8 Bits 8 Bits (Octet) (Octet) (Octet) (Octet) 8 Bits 8 Bits 8 Bits 8 Bits Network Host Complete IPv4 Address

  15. IPv4 Addressing 192 168 0 1 255 255 0 0 11000000 10101000 00000000 00000001 11111111 11111111 00000000 00000000 11000000 10101000 00000000 00000000 Network 192 168 0 0

  16. Network and Broadcast The first address in a subnet is always the subnet ID and the last is always the broadcast address for the network. So for our example: • 192.168.0.0 Network ID • 255.255.255.0 Subnet Mask • 192.168.0.1 to .254 Host IP Addresses • 192.168.0.255 Broadcast Address

  17. IP addressing good practice • If there is a router / gateway on the network it is usually found at the lowest IP address • In our example it would be 192.168.0.1 • This is traditionally due to some protocols such as RSTP and IGMP which elect the lowest IP address device to be the master

  18. Only through Gateways can devices talk to different networks Gateway 192.168.2.1/24 Gateway 192.168.4.1/24 Network 192.168.2.0/24 Network 192.168.4.0/24

  19. Summary of course so far We have covered: The 7 layer OSI model Network topologies Network devices Ethernet addressing IP addressing

  20. Practical Setup a small network between laptops • Decide IP address’s to use • Decide network topology AIM: To be able to ping all other devices in the network Use Wireshark to monitor network traffic

  21. Test paper • Name a layer 3 device • ___________________ • Name a layer 2 device • ___________________ • How many layers are there in the OSI model? • ___________________ • How many bits are there in an IP address? • ___________________ • 5. A device which operates at layer 3 or higher will have a logical ____ address and a hard-coded ____ address. • 6. The subnet mask allows computers to calculate the _______ and _______ portions of its own IP address • What type of network topologies are the following? • ______________ • ______________ • What do the following acronyms stand for? • LAN: _________________ • WAN: _________________ • IP: _________________

  22. Test paper • Name a layer 3 device • __Router / Redfox______ • Name a layer 2 device • __Switch / Lynx________ • How many layers are there in the OSI model? • _______7____________ • How many bits are there in an IP address? • ________32___________ • 5. A device which operates at layer 3 or higher will have a logical _IP__ address and a hard-coded _MAC___ address. • 6. The subnet mask allows computers to calculate the ___HOST____ and _Network_ portions of its own IP address • What type of network topologies are the following? • __STAR______ • __BUS_________ • What do the following acronyms stand for? • LAN: _Local Area Network_ • WAN: _Wide Area Network_ • IP: _Internet Protocol__

  23. Types of Network Traffic • Unicast - one to one • Broadcast - one to all • Multicast - one to many

  24. Types of Network Traffic cont… • UDP - User Datagram Protocol • TCP - Transmission Control Protocol UDP is like sending a letter using standard post - no notification of delivery TCP is like sending a letter via recorded post – you get a message back giving delivery confirmation

  25. TCP and UDP Ports • IP address is the postal address • UDP or TCP is the type of delivery • Ports are the person the letter is for smtp modbus Port: 80 Port: 21 Port: 502 Port: 25 http ftp

  26. ARP request packet: To: 255.255.255.255 Whois: 192.168.50.100 Tell 192.168.50.1 ARP reply packet: To: 192.168.50.1 I am:192.168.50.100! My MAC address is: 04:CA:15:99:B2:0A How devices communicate with each other: ARP 192.168.50.100 192.168.50.1 Ah! A broadcast packet, I better read this… I need to send some data to 192.168.50.100 I don’t know which device has that IP Address! Host 192.168.50.1 is looking for 192.168.50.100… that’sME! I had better tell him my physical address so that he can communicate directly with me. Aha! Host 192.168.50.100 replied, and he is on my local network! Now I know exactly where to send the data

  27. Device Device Port Port 1 1 2 2 3 3 ARP and MAC tables in Switches A B A I need to send some data to 192.168.50.100 Etc. etc… A B B A

  28. Device Device Device Device Port Port Port Port 1 1 1 1 2 2 2 2 3 3 3 3 Learning, Flooding and Forwarding Im going to send out an ARP request!! This looks like a BROADCAST packet of data. Im going to FLOOD it out of all my connected ports Hey, some guy calling himself “A” wants to know my MAC address! Suppose I better tell him.. B A C D A A C C C A A

  29. Switch MAC Tables 00:00:00:00:00:00 There has been no activity from this device for a while so the switch will remove the entry from the MAC table. This is known as MAC Ageing

  30. Communication session established! How devices communicate with each other: TCP I received some messages! I am expecting message 4 next. Sending message: Sending message: 1 2 3 4 5 6 192.168.50.100 Hey! I need to send you some data! 192.168.50.1 OK! Send me 3 messages at a time. Alright! Get ready! Sends data Acknowledges data

  31. No session established! How devices communicate with each other: UDP I received some messages! Sending message: Sending message: * * * * * * 192.168.50.100 Hey! I need to send you some data! 192.168.50.1 I hope you are ready! Sends data

  32. Connecting to other networks • So far we have covered Local Area Networks or LANs • What if we wish to talk to another LAN or remote network? • A Gateway / Router is used.

  33. The most common mistake made is forgetting to enter the Gateway address in a device that needs to communicate with another network

  34. Network: 192.168.10.0 Network: 10.10.50.0 A Typical Communication In Full I’ve received a packet from a device! Now I know that C is connected to me, he is looking for a Mac address I don’t know the location of. ARP! Aha! Someone is looking for me! I’ll tell him I am here – I only know his IP address right now – I best find his MAC This UDP packet needs to go to the 10.10.50.0 network. I know how to get there because I’ve got a VPN tunnel to him! R1 R2 Hmm, I havent spoken to my gateway’s IP before – I don’t know his mac address, I had better find out! This packet of data needs to go to 10.10.50.100, ive spoken to him recently so I know his MAC address. ARP! ARP! ARP! This packet is destined for a MAC address I’ve seen recently. I know its connected to one of my ports. This ARP reply is destined for C, I’ve spoken to him recently! I know that address is not on my own network – I wont be able to contact it directly I’ll let my gateway handle this one! From: <Mac add. Of C> Who has: 192.168.10.1? Whew! Now I know how to reach my gateway! I’ll start sending data to 10.10.50.100 B C A ARP! UDP ARP! D E F 192.168.10.1 wants to know my MAC address – I’ll gladly tell him. I am programmed to send data to 10.10.50.100 Ooh lovely! Data for me!

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