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CIT 384: Network Administration

CIT 384: Network Administration. Switches. Topics. TCP/IP Architecture OSI Reference Model Cisco certification overview. Switching at Data Link Layer. Forwards Ethernet frames between two devices on same LAN. Logical link control Flow control Error correction Media access control

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CIT 384: Network Administration

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  1. CIT 384: Network Administration Switches CIT 384: Network Administration

  2. Topics • TCP/IP Architecture • OSI Reference Model • Cisco certification overview CIT 384: Network Administration

  3. Switching at Data Link Layer • Forwards Ethernet frames between two devices on same LAN. • Logical link control • Flow control • Error correction • Media access control • Who can transmit when. • Breaks data into frames. CIT 384: Network Administration

  4. Hubs Advantages over 10BASE2 bus • Problem on 1 cable didn’t impact entire network. • Easier to run cables for star topology. Disadvantages of hubs • Collisions • Shared bandwidth, only one device can send at a time. • Broadcasts seen by all hosts. CIT 384: Network Administration

  5. Bridges A bridge segments a network into two parts. • Each part is a collision domain. • Frames in domain A can collide with each other. • But they cannot collide with frames in domain B. Bridges buffer packets. • If domain A is busy, then frame is buffered until the segment is no longer busy. CIT 384: Network Administration

  6. Bridges Bridges reduce collisions + add bandwidth. CIT 384: Network Administration

  7. Switches A switch works like a collection of bridges. • Each port is its own collision domain. • If only one device connected to a port, the switch can communicate at full duplex. CIT 384: Network Administration

  8. Ethernet Address Types Unicast addresses represent a single device. Multicast addresses represent a subset of devices on the LAN. They begin with 0100.5E The broadcast address represents all devices on the LAN. It is FFFF.FFFF.FFFF CIT 384: Network Administration

  9. Switch Functions • Decide whether to forward a frame or not, based on its destination MAC address. • Learn MAC addresses by examining source MAC addresses received. • Create a layer 2 loop-free environment using Spanning Tree Protocol (STP.) CIT 384: Network Administration

  10. Forwarding Frames • Switch receives frame on a port. • Extracts destination MAC address from Ethernet header. • Looks up destination MAC address in internal address table. • Forwards frame to port specified in table unless that port is the same port on which the frame was received. • If no entry exists in table for MAC address, forward the frame out all interfaces except the port it originated from. CIT 384: Network Administration

  11. CIT 384: Network Administration

  12. Learning MAC Addresses • Switch receives frame on a post. • Retrieves source MAC address from Ethernet header of frame. • Searches address table for MAC address. • If MAC address not found, add the (MAC address, port) pair to the table. CIT 384: Network Administration

  13. MAC Address Table Switches have a finite amount of memory. • Can only store a fixed # of addresses. Maintain an inactivity timer for each address. • Timer reset to 0 each time address is seen. • If switch runs out of space, oldest entries are removed from table. CIT 384: Network Administration

  14. Loops • Bob is off, so no switch has his address. • Therefore switches flood frames to Bob. • Switches receive flood from other switches, which they flood again, looping indefinitely. CIT 384: Network Administration

  15. Avoiding Loops Don’t have physically redundant switches. • Redundancy is needed for reliability. • It’s easy for someone to add a switch and create a loop in a complex campus network. Create a logical network without loops: STP. • Dynamically disable switch ports that could allow loops. • Re-enable disabled ports when a link fails so that network retains benefit of redundancy. CIT 384: Network Administration

  16. Collision Domains A collision domain is the set of devices whose frames can collide with each other. Bridges, switches, and routers separate the network into collision domains. CIT 384: Network Administration

  17. Collision Domains • All devices share the available bandwidth. • Bandwidth may be inefficiently used due to effects of collision, especially under high use. CIT 384: Network Administration

  18. Broadcast Domains A broadcast domain is the set of devices for which, when one device sends a broadcast, all devices receive the broadcast. Routers separate the network into broadcast domains. CIT 384: Network Administration

  19. Broadcast Domains • Bandwidth is not shared. • Some bandwidth and processing may be wasted by broadcasts in large domains. • A LAN consists of all devices in the same broadcast domain. CIT 384: Network Administration

  20. Segmenting Device Features CIT 384: Network Administration

  21. Virtual LANs (VLANs) Without VLANs, switches consider all devices on same broadcast domain (LAN.) With VLANs • Switch can support multiple broadcast domains. • Assign ports to specific VLANs. CIT 384: Network Administration

  22. VLAN Purposes • Create more flexible network designs, without having more switches. • Segment devices into smaller broadcast domains to increase performance. • Reduce STP workload by limiting VLAN to a single access switch. • To enforce security by aggregating sensitive hsots on specific VLANs. • To separate VOIP traffic from PC traffic. CIT 384: Network Administration

  23. Switch Design Hierarchy Three layers • Access • Distribution • Core Differences • Whether switch connects to end-user devices. • Whether switch should forward frames between other switches by connecting to multiple different switches. CIT 384: Network Administration

  24. Switch Layers Access switches • Connect directly to end-user devices. • Send traffic to connected end-user devices. • Send other traffic to distribution layer. Models • Catalyst 3750 • Catalyst 3560 • Catalyst 2960 Catalyst 3750 switches CIT 384: Network Administration

  25. Distribution Switches • Provide path through which access switches can forward traffic to each other. • Models • Catalyst 6500 • Catalyst 4500 CIT 384: Network Administration

  26. Core Switches • Aggregate distribution switches. Not needed on smaller networks. • Models • Catalyst 6500 • Nexus 7000 CIT 384: Network Administration

  27. CIT 384: Network Administration

  28. Catalyst 2960 Ethernet ports • 29600-24TT-L: 24 10/100 + 2 10/100/1000 ports • Series ranges from 8+1 to 48 gigabit ports. Operating System: Cisco IOS Other features • Some models support Power over Ethernet • QoS support for IP phones • Security features (MAC binding, NAC) CIT 384: Network Administration

  29. Catalyst 2960 LEDs CIT 384: Network Administration

  30. Accessing the IOS CLI CIT 384: Network Administration

  31. CLI Access Methods Console • 9600 bps 8N1 serial connection • Available before switch has been configured. • Available during problems: down network, OS. • Only one connection at a time. ssh and telnet • Switch must be configured with an IP address. • Provides remote access from anywhere on net. • Up to 16 simultaneous connections. • All data (including passwords) revealed by telnet, so ssh is preferred. CIT 384: Network Administration

  32. CLI configuration CIT 384: Network Administration

  33. User and Enable Mode User Exec mode can read most data. Enable mode is needed to reconfigure switch. CIT 384: Network Administration

  34. Cisco IOS Internetwork Operating System • Multitasking, no memory protection • CLI copied by many network vendors. IOS is available with different feature sets: • IP data • Voice + data • Security + VPN Older switches run CatOS CIT 384: Network Administration

  35. CLI Help Features CIT 384: Network Administration

  36. CLI Editing CIT 384: Network Administration

  37. Configuration Mode Commands in Configuration Mode update the active configuration file. CIT 384: Network Administration

  38. Configuration Submodes CIT 384: Network Administration

  39. Example CLI Session Switch> enable Switch# configure terminal Switch(config)# enable secret letmein Switch(config)# interface FastEthernet 0/1 Switch(config-if)# speed 100 Switch(config-if)# ip address 10.1.1.1 255.0.0.0 Switch(config-if)# no shutdown Switch(config-if)# exit Switch(config)# line console 0 Switch(config-line)# password spam Switch(config-line)# exit Switch(config)# copy running-config startup-config Switch(config)# disable Switch> CIT 384: Network Administration

  40. Switch Memory Types RAM: Working storage, includes the active configuration file. ROM: Stores boot program that finds Cisco IOS image and loads into RAM. Flash: Stores IOS image and other files. NVRAM: Stores startup configuration file that is used when switch is booted. CIT 384: Network Administration

  41. Switch Configurations Configurations Running: currently used config in RAM. Startup: will be used at next reboot. Viewing show running-config show startup-config Saving running-config (replaces old startup) copy running-config startup-config CIT 384: Network Administration

  42. References • James Boney, Cisco IOS in a Nutshell, 2nd edition, O’Reilly, 2005. • Cisco, Catalyst 2960 series switches, http://www.cisco.com/en/US/products/ps6406/index.html, 2008. • Cisco, Cisco Connection Documentation, http://www.cisco.com/univercd/home/home.htm • Cisco, Internetworking Basics, http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/introint.htm • Wendell Odom, CCNA Official Exam Certification Library, 3rd edition, Cisco Press, 2007. • Priscilla Oppenheimer and Joseph Bardwell, Troubleshooting Campus Networks, Addison-Wesley, 2002. • W. Richard Stevens, TCP/IP Illustrated, Addison-Wesley, 1994. CIT 384: Network Administration

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