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Local Internets

Local Internets. Cabletron SmartSwitch 2100. Local Internets. Internet System of subnets such that any station on any subnet can communicate with any station on any other subnet by placing the receiver’s address in a message Subnets are individual networks in an internet. Local Internets.

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Local Internets

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  1. Local Internets Cabletron SmartSwitch 2100

  2. Local Internets • Internet • System of subnets such that any station on any subnet can communicate with any station on any other subnet by placing the receiver’s address in a message • Subnets are individual networks in an internet

  3. Local Internets LAN LAN LAN LAN • Local Internets • Links multiple LANs at a single site • Entirely on customer premises • Planned and managed by the owner • Company has no limits • Company has all the headaches • High-speed transmission (roughly LAN speeds)

  4. Why a Local Internet? • Overcome distance limitations • 10Base-T networks span only 500 meters • Overcome congestion and latency • Individual shared media networks running around 10 Mbps become saturated at 200-300 stations. • Connect dissimilar LANs • Link Ethernet and Token-Ring Network LANs

  5. Local Internetting to Increase Distance Spans Internetting Device 10Base-T LAN in Headquarters Building (500 m maximum distance) HQ LAN Transmission Link (no max distance) Internetting Device 10Base-T LAN in Factory Building (500 m maximum distance) Factory LAN

  6. A Congested Shared Media LAN Before: Single LAN Department 1: 150 Stations Department 2: 150 Stations Stations A B C D Stations All stations in Department 2 hear the message B transmits to A Each station hears the traffic of 300 stations: Heavily congested.

  7. Internetting keep most traffic within LANs After Resegmentation Department 1: 150 Stations Department 2: 150 Stations Internetting Device Stations A B C D Stations Internetting Device Blocks the Transmission of this message to Department 2 B transmits to A Traffic of 150 stations: Not Congested Traffic of 150 stations: Not Congested

  8. Internetting Devices: Bridges • Simple, automatic, inexpensive, fast • Usually only two ports • A fast, cost-effective choice for small internets • See CISCO whitepaper for more details

  9. Multiple Bridges LAN 2 X LAN 3 LAN 1 No Loops Allowed Problematic for large bridged internets LAN 4 LAN 5

  10. Multiple Bridges Route Between LANs 1, 5 LAN 2 LAN 3 X LAN 1 No loops means only one path between LANs No alternative routing if failures, congestion No way to optimize routing for security, etc. LAN 5

  11. 802.1 Spanning Tree Standard Route Between LANs 1, 5 LAN 2 LAN 3 Backup Link LAN 1 Allows backup links Disabled during normal operation If a failure occurs, automatically initiated LAN 5

  12. Bridging LANs with Different Physical and MAC Layers Bridge 802.5 Token-Ring Network 802.3 10Base-T Ethernet LAN Hub 10Base-T Connection 802.5 Connection

  13. Bridging LANs with Different Physical and MAC Layers 802.2 LLC Standard 802.2 LLC Standard LLC Layer (Same) 802.1 Bridging Standard 802.1 Bridging Standard Bridging Layer (Same) 802.5 MAC Layer (Token-Passing) 802.3 MAC Layer (CSMA/CD) MAC Layer (Different) 802.5 Connection to Access Unit Physical Layer (Different) 10Base-T Connection to Hub

  14. Problems of Bridges • Do Not Stop Broadcast Messages • Servers broadcast their existence about twice a minute • In contrast to normal messages, which are designed to go to single stations, broadcast messages go to all stations. • Goes to all stations on the network; bridges pass these messages on • Problematic in large bridged intranets

  15. Problems of Bridges • Do Not Stop Any Client from Logging into Any Server • Poor security. Only password protection on servers • Bad if servers hold grades in a university • Bad for departmental servers holding key personnel or financial data in a firm

  16. Switches Solve Bridge Problems • Begin as Multiport Bridges • Add broadcast reduction, security

  17. Simple Switched Internet Connection 1 LAN A Connection 1 LAN C No Waiting! LAN B Connection 2 Switches can carry messages between several pairs of LANs simultaneously. Connection 2 LAN D

  18. Switched Internet with Multiple Switches Switch A Switch B Switch C Switch D LAN 1 LAN 2 Switches are arranged in a hierarchy Only one route between any two LANs No routing around failure, congestion No optimization of routes Route: 1-B-A-C-2

  19. Switch Hierarchy • Switches can be arranged hierarchically • Levels of Switches • Desktop switches (only a few MAC addresses can be supported) • Workgroup switches (MAC addresses for members of a department) • Enterprise switches (large number of MAC addresses)

  20. Virtual LANs Reduce Broadcasting • Stations are Divided into Groups • Called Virtual LANs (VLANs) • Server, other broadcasts limited to VLANs • Not to all stations on all ports LAN A LAN B LAN C LAN D Server only broadcasts to its VLAN stations on LAN A, LAN C

  21. VLANs Add Security • Only stations on the same VLAN as a server can reach it to log in On VLAN 36 On VLAN 7 X LAN A LAN B LAN C LAN D Client can only reach server if they are on the same VLAN

  22. Simple Local Internet Using Ethernet Switching and 10Base-T Ethernet Switch 10Base-T Hub 10Base-T Hub 10Base-T Hub In a switched Ethernet internet: Stations connect to hubs. Hubs connect to switches. LAN LAN

  23. Switched Internets • The Move Toward Switched Networks • All-switched LANs with stations connected to switches are still too expensive for most firms. Need a port for each station. • Using switches as internetting devices is cost-effective today. Only hubs connect to switches. Only need a port for each hub • As switching costs fall, companies can later move switching down to individual LANs by replacing hubs by switches. See CISCO white paper for details.

  24. Routers • Most sophisticated internetting devices • Provide services for linking thousands of subnets • Used in the worldwide Internet, also within firms • Efficient for long-distance transmission • Provide wide range of management services to give relatively automatic operation • By far the most expensive internetting devices

  25. Route • End-to-End Connection 1 LAN A LAN B 3 2 4 LAN D LAN A - 1 - 3 - 5 - LAN D 5

  26. Alternative Routes • Multiple Ways to Get from LAN A to LAN D 1 LAN A LAN B 3 2 4 A-1-3-5-D A-1-3-4-D A-2-5-D Etc. LAN D 5

  27. Advantages of Alternative Routing • Routing Around Failures • Failed switches, trunk lines connecting switches • Routing Around Congestion • More common than outright failures • Route Optimization • Least cost route • Most reliable route • Most secure route, etc.

  28. Mixing Switches and Routers Site A LAN LAN Site B Switch LAN Router Switch Router LAN Site C Router

  29. Distributed Backbone Network LAN 1 LAN 2 FDDI Backbone Ring Router Router Router LAN 3

  30. Backbone Network • Network that Links Subnets • Subnets take the place of stations • Distributed Backbone • Backbone runs past all stations • If a single router (or other internettingdevice) fails, only that station is disconnected • FDDI is popular because of its possible 200 km circumference, 100 Mbps speeds

  31. Local Internet Using Collapsed Backbone LAN A LAN B LAN C Routers at LANs Routers at LANs Central Switch or Router

  32. Collapsed Backbone • Single point of maintenance • Easy to maintain the network • Single point of failure • If the central device fails, serious problems • Types of central devices • Switches • Routers

  33. OSI Layers • Layer 1 (Physical) • Electrical signaling over a physical link • Layer 2 (Data Link) • Data framing and administration of communication over a single data link • Point to point connection • Shared media LAN with only one possible path between two station • Layer 3 (Network) • Routing across an internet with multiple alternative routes • Or a subnet that offers alternative routes, but these rarely exist

  34. Internetting Devices • Hubs • Layer 1: merely reflect bits back out • Bridges, Switches • Layer 2: Work with MAC addresses • No alternative routing • Routers • Layer 3: routing across internet • Only device with alternative routing

  35. TCP/IP Internetting TCP/IP OSI Application Transport Internet • Subnet layer • Links stations on same subnet • Often IEEE LAN standards • PPP for telephone connections • TCP/IP specifies almost any subnet standard • For LANs, etc., specifies OSI • OSI further subdivides into Physical, Data Link Subnet Data Link Physical

  36. Application TCP/IP Internetting Transport Internet Subnet • Internet layer: • Links stations across internets • Main standard is the Internet Protocol (IP) • Dominant protocol for routers

  37. Application TCP/IP Internetting Transport Internet Subnet • Transport layer: • Links computers, even if different platforms • Main standards are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) • Application layer: • Links application programs even if from different vendors • Many standards, because many applications • SMTP for e-mail; HTTP for the WWW, etc.

  38. Universal Addressing • Each host has a unique IP Number • 32-bit binary number • Goes in the IP header’s source and destination fields • 10000000101010110001000100001101 • Impossible to remember Source Destination 4 Bytes 4 Bytes IP Packet

  39. Subnet Mask • Problem: IP numbers do not include subnetting • Solution: Create a second number: a Subnet Mask • Define which bits of the IP address refer to subnets vs. hosts on subnet • Subnet mask is 32 bits long, in dot quad format • See last meeting TCP/IP in NT for basic IP and Subnet Mask concepts.

  40. Routers • Routers also get IP addresses • So packets can be sent to them for routing • Has network ID of the network on which it sits • Must be assigned a host ID • Example: 128.171.17.1 128.171.17.104 IP Packet for Delivery Default Router Another Router 128.171.17.1

  41. Routers • Subnets can have Multiple Routers • There is usually a default router for packet delivery • Default router is used if no router is specified • Routers are sometimes called gateways in TCP/IP IP Packet for Delivery Default Router Other Router

  42. Routing Protocols Routing Table There are no “master” routers. Each router works independently to do routing. This requires each router to build a “routing table” that contains information about the locations of other routers.

  43. Routing Protocols Routing Table Routing protocols allow routers to exchange information in their routing tables.

  44. Peer Control Among Routers • Routers Communicate Among Themselves • To coordinate their actions without central control • Share knowledge of network connectivity • Common standards are RIP, OSPF, BGP Router Coordination Message

  45. Routing Protocols • RIP - Router Information Protocol • High overhead, but simple and OK for small networks • OSPF - Open Shortest Path First • Optimizes routing, but complex • BGP - Border Gateway (Router) Protocol • Used in Internet Backbone Routers • Read Cisco whitepaper for more on routing

  46. Autonomous Systems RIP or OSPF Autonomous Router Organization can select any routing protocol to synchronize its autonomous (internal) routers. RIP and OSPF are common. Border routers that linkautonomous systems normally use BPG. RIP or OSPF Border Router BPG Autonomous System Border Router

  47. Error Handling • TCP/IP a comprehensive set of error handling processes • The Internet Control Message Protocol (ICMP) is used to send error messages. • Hosts, Routers send ICMP messages to one another if a problem occurs • “Host not found” is a common ICMP error message. ICMP Error Message Host Router

  48. Internet Control Message Protocol (ICMP) The Internet Control Message Protocol (ICMP) is for delivering supervisory messages among hosts and routers

  49. Internet Control Message Protocol (ICMP) “Host Unreachable” Error Messages

  50. Internet Control Message Protocol (ICMP) Flow Control “Source Quench” tells host to reduce transmission rate. Source Quench

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