CIT 384: Network Administration

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