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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 • 100Base-T networks span only 500 meters • Overcome congestion and latency • Individual shared media networks running around 100 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 100Base-T LAN in Headquarters Building (500 m maximum distance) HQ LAN Transmission Link (no max distance) Internetting Device 100Base-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. 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

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

  24. 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

  25. 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.

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

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

  28. 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, but Gigabit Ethernet gaining.

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

  30. 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

  31. Backbone Network Architectures • Identifies the way backbone interconnects LANs • Defines how it manages packets moving through BB • Fundamental architectures • Bridged Backbones • Routed Backbones • Collapsed Backbones • Rack-based • Chassis-based • Virtual LANs • Single-switch VLAN • Multiswitch VLAN

  32. Backbone Architecture Layers • Access Layer (not part of BB) • Closest to the users; • Backbone Design Layers • Distribution Layer • Connects the LANs together (often in one building • Core Layer (for large campus/enterprise networks) • Connects different BNs together (building to building)

  33. Bridged Backbone bus topology Entire network is just one subnet

  34. Bridged Backbones • Move packets between networks based on their data link layer addresses • Cheaper (since bridges are cheaper than routers) and easier to install (configure) • Just one subnet to worry • Change in one part may effect the whole network • Performs well for small networks • For large networks broadcast messages (e.g., address request, printer shutting down) can lower performance • Formerly common in the distribution layer • Declining due to performance problems

  35. Example of a routed BB at the Distribution layer Routed Backbone Usually a bus topology Each LAN is a separate subnet

  36. Routed Backbones • Move packets using network layer addresses • Commonly used at the core layer • Connecting LANs in different buildings in the campus • Can be used at the distribution layer as well • LANs can use different data link layer protocols • Main advantage: LAN segmentation • Each message stays in one LAN; unless addressed outside the LAN • Easier to manage • Main disadvantages • Tend to impose time delays compared to bridging • Require more management than bridges & switches

  37. Most common type BB mainly used in distribution layer Collapsed Backbone A connection to the switch is a separate point-to-point circuit Star topology

  38. Collapsed Backbones • Replaces the many routers or bridges of the previous designs • Backbone has more cables, but fewer devices • No backbone cable used; switch is the backbone. • Advantages: • Improved performance (200-600% higher) • Simultaneous access; :switched” operations • A simpler more easily managed network – less devices • Two minor disadvantages • Use more and longer cables • Reliability: • If the central switch fails, the network goes down.

  39. Rack-Based Collapsed Backbones • Places all network equipment (hubs and switch) in one room (rack room) • Easy maintenance and upgrade • Requires more cables (but cables are cheap) • Main Distribution Facility (MDF) or Central Distribution Facility • Another name for the rack room • Place where many cables come together • Patch cables used to connect devices on the rack • Easier to move computers among LANs • Useful when a busy hub requires offloading

  40. Chassis-Based Collapsed Backbones • Use a “chassis” switch instead of a rack • A collection of modules • Number of hubs with different speeds • L2 switches • Example of a chassis switch with 710 Mbps capacity • 5 10Base-T hubs, 2 10Base-T switches (8 ports each) • 1 100Base-T switch (4 ports), 100Base-T router •  ( 5 x 10) + (2 x 10 x 8) + (4 x 100) + 100 = 710 Mbps • Flexible • Enables users to plug modules directly into the switch • Simple to add new modules

  41. Virtual LANs (VLANs) • A type of LAN-BN architecture • Made possible by high-speed intelligent switches • Computers assigned to LAN segments by software • Often faster and provide more flexible network management • Much easier to assign computers to different segments • More complex and so far usually used for larger networks • Basic VLAN designs: • Single switch VLANs • Multi-switch VLANs

  42. Single Switch VLAN Collapsed Backbone acting as a large physical switch Computers assigned to different LANs by software Switch

  43. Types of Single Switch VLANs • Port-based VLANs (Layer 1 VLANs) • Use physical layer port numbers on the front of the VLAN switch to assign computers to VLAN segments • Use a special software to tell the switch about the computer - port number mapping • MAC-based VLANs (Layer 2 VLANs) • Use MAC addresses to form VLANs • Use a special software to tell the switch about the computer - MAC address mapping • Simpler to manage • Even if a computer is moved and connected to another port, its MAC address determines which LAN it is on

  44. Types of Single Switch VLANs • IP-based VLANs (Layer 3 VLANs, protocol based VLANs) • Use IP addresses of the computers to form VLANs • Similar to MAC based approach (use of IP instead of MAC address) • Application-based VLANs (Layer 4 VLANs, policy-based VLANs) • Use a combination of • the type of application (Indicated by the port number in TCP packet) and • The IP address to form VLANs • Complex process to make assignments • Allow precise allocation of network capacity

  45. Multi-switch VLAN-Collapsed Backbone Switch Switch Switch Switch

  46. Multi-switch VLAN Operations • Inter-switch protocols • Must be able to identify the VLAN to which the packet belongs • Use IEEE 802.1q • When a packet needs to go from one switch to another • 16-byte VLAN tag inserted into the 802.3 packet by the sending switch • When the IEEE 802.1q packet reaches its destination switch • Its header (VLAN tag) stripped off and Ethernet packet inside is sent to its destination computer

  47. VLAN Operating Characteristics • Advantages of VLANs • Faster performance • Precise management of traffic flow • Ability to allocate resources to different type of applications • Traffic prioritization (via 802.1q VLAN tag) • Include in the tag: a priority code based on 802.1p • Can have QoS capability at MAC level • Similar to RSVP and QoS capabilities at network and transport layers • Drawbacks • Cost • Management complexity

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