1 Local Internets Cabletron SmartSwitch 2100

2 Local Internets ä Internet ä 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 ä Subnets are individual networks in an internet

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

4 Why a Local Internet? ä Overcome distance limitations ä 100Base-T networks span only 500 meters ä Overcome congestion and latency ä Individual shared media networks running around 100 Mbps become saturated at stations. ä Connect dissimilar LANs ä Link Ethernet and Token-Ring Network LANs

5 Local Internetting to Increase Distance Spans 100Base-T LAN in Headquarters Building (500 m maximum distance) 100Base-T LAN in Factory Building (500 m maximum distance) Transmission Link (no max distance) Internetting Device Internetting Device HQ LAN Factory LAN

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

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

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

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

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

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

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

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

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

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

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

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

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

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

20 Virtual LANs Reduce Broadcasting ä Stations are Divided into Groups ä Called Virtual LANs (VLANs) ä Server, other broadcasts limited to VLANs ä 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 ä Only stations on the same VLAN as a server can reach it to log in LAN A LAN B LAN C LAN D Client can only reach server if they are on the same VLAN On VLAN 7 On VLAN 36 X

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

23 Route ä End-to-End Connection LAN A LAN D LAN B LAN A LAN D

24 Alternative Routes ä Multiple Ways to Get from LAN A to LAN D LAN A LAN D LAN B A DA DA-2-5-DEtc.

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

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

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

28 Backbone Network ä Network that Links Subnets ä Subnets take the place of stations ä Distributed Backbone ä Backbone runs past all stations ä If a single router (or other internetting device) fails, only that station is disconnected ä 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 ä Single point of maintenance ä Easy to maintain the network ä Single point of failure ä If the central device fails, serious problems ä Types of central devices ä Switches ä Routers

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

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

33 Bridged Backbone bus topology Entire network is just one subnet

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

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

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

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

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

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

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

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

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

43 Types of Single Switch VLANs ä Port-based VLANs (Layer 1 VLANs) ä Use physical layer port numbers on the front of the VLAN switch to assign computers to VLAN segments ä Use a special software to tell the switch about the computer - port number mapping ä MAC-based VLANs (Layer 2 VLANs) ä Use MAC addresses to form VLANs ä Use a special software to tell the switch about the computer - MAC address mapping ä Simpler to manage ä 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 ä IP-based VLANs (Layer 3 VLANs, protocol based VLANs) ä Use IP addresses of the computers to form VLANs ä Similar to MAC based approach (use of IP instead of MAC address) ä Application-based VLANs (Layer 4 VLANs, policy-based VLANs) ä Use a combination of ä the type of application (Indicated by the port number in TCP packet) and ä The IP address to form VLANs ä Complex process to make assignments ä Allow precise allocation of network capacity

45 Multi-switch VLAN-Collapsed Backbone Switch

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

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