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Building a Simple Network

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  1. Understanding Ethernet Building a Simple Network

  2. Local Area Network

  3. LAN Components • Computers • PCs • Servers • Interconnections • NICs • Media • Network devices • Hubs • Switches • Routers • Protocols • Ethernet • IP • ARP • DHCP

  4. Functions of a LAN • Data and applications • Share resources • Provide communication path to other networks

  5. LAN Sizes

  6. Ethernet Evolution

  7. LAN Standards

  8. Ethernet Frame Structure

  9. Communicating Within the LAN

  10. MAC Address Components

  11. Understanding the Challenges of Shared LANs Ethernet LANs

  12. LAN Segment Limitations • Signals degrade with transmission distance. • Each Ethernet type has a maximum segment length.

  13. Extending LAN Segments • Shares bandwidth • Extends cable distances • Repeats or amplifies signal

  14. Collisions

  15. CSMA/CD

  16. Solving Network Challenges with Switched LAN Technology Ethernet LANs

  17. Network Congestion • High-performance PCs • More networked data • Bandwidth-intensive applications

  18. Bridges • Operate at Layer 2 of the OSI model • Forward, filter, or flood frames • Have few ports • Are slow

  19. LAN Switch • High port density • Large frame buffers • Mixture of port speeds • Fast internal switching • Switching modes: • Cut-through • Store-and-forward • Fragment-free

  20. LAN Switch Features

  21. Switches Supersede Bridges • Operate at Layer 2 of the OSI model • Forward, filter, or flood frames • Have many ports • Are fast

  22. Switching Frames

  23. LANs Today • Users grouped by physical location • More switches added to networks • Switches connected by high-speed links

  24. Implementing VLANs and Trunks Medium-Sized Switched Network Construction

  25. Issues in a Poorly Designed Network • Unbounded failure domains • Large broadcast domains • Large amount of unknown MAC unicast traffic • Unbounded multicast traffic • Management and support challenges • Possible security vulnerabilities

  26. VLAN Overview • Segmentation • Flexibility • Security VLAN = Broadcast Domain = Logical Network (Subnet)

  27. Designing VLANs for an Organization • VLAN design must take into consideration the implementation of a hierarchical network addressing scheme. • The benefits of hierarchical addressing are: • Ease of management and troubleshooting • Minimization of errors • Reduced number of routing table entries

  28. Guidelines for Applying IP Address Space • Allocate one IP subnet per VLAN. • Allocate IP address spaces in contiguous blocks.

  29. VLAN Operation

  30. VLAN Membership Modes

  31. 802.1Q Trunking

  32. 802.1Q Frame

  33. Understanding Native VLANs

  34. Configuring 802.1Q Trunking SwitchX(config-if)# switchport mode {access | dynamic {auto | desirable} | trunk} • Configures the trunking characteristics of the port SwitchX(config-if)# switchport mode trunk • Configures the port as a VLAN trunk

  35. Verifying a Trunk SwitchX# show interfaces interface [switchport | trunk] SwitchX# show interfaces fa0/11 switchport Name: Fa0/11 Switchport: Enabled Administrative Mode: trunk Operational Mode: down Administrative Trunking Encapsulation: dot1q Negotiation of Trunking: On Access Mode VLAN: 1 (default) Trunking Native Mode VLAN: 1 (default) . . . SwitchX# show interfaces fa0/11 trunk Port Mode Encapsulation Status Native vlan Fa0/11 desirable 802.1q trunking 1 Port Vlans allowed on trunk Fa0/11 1-4094 Port Vlans allowed and active in management domain Fa0/11 1-13

  36. VLAN Creation Guidelines • The maximum number of VLANs is switch-dependent. • Most Cisco Catalyst desktop switches support 128 separate spanning-tree instances, one per VLAN. • VLAN 1 is the factory default Ethernet VLAN. • Cisco Discovery Protocol and VTP advertisements are sent on VLAN 1. • The Cisco Catalyst switch IP address is in the management VLAN (VLAN 1 by default). • If using VTP, the switch must be in VTP server or transparent mode to add or delete VLANs.

  37. Adding a VLAN SwitchX# configure terminal SwitchX(config)# vlan 2 SwitchX(config-vlan)# name switchlab99

  38. Verifying a VLAN SwitchX# show vlan [brief | id vlan-id || name vlan-name] SwitchX# show vlan id 2 VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 2 switchlab99 active Fa0/2, Fa0/12 VLAN Type SAID MTU Parent RingNo BridgeNo Stp BrdgMode Trans1 Trans2 ---- ----- ---------- ----- ------ ------ -------- ---- -------- ------ ------ 2 enet 100002 1500 - - - - - 0 0 . . . SwitchX#

  39. Assigning Switch Ports to a VLAN SwitchX(config-if)# switchport access [vlan vlan# | dynamic] SwitchX# configure terminal SwitchX(config)# interface range fastethernet 0/2 - 4 SwitchX(config-if)# switchport access vlan 2 SwitchX# show vlan VLAN Name Status Ports ---- -------------------------------- --------- ---------------------- 1 default active Fa0/1 2 switchlab99 active Fa0/2, Fa0/3, Fa0/4

  40. Verifying VLAN Membership SwitchX# show vlan brief SwitchX# show vlan brief VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Fa0/1 2 switchlab99 active Fa0/2, Fa0/3, Fa0/4 3 vlan3 active 4 vlan4 active 1002 fddi-default act/unsup 1003 token-ring-default act/unsup VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1004 fddinet-default act/unsup 1005 trnet-default act/unsup

  41. Verifying VLAN Membership (Cont.) SwitchX(config-if)# show interfaces interface switchport SwitchX# show interfaces fa0/2 switchport Name: Fa0/2 Switchport: Enabled Administrative Mode: dynamic auto Operational Mode: static access Administrative Trunking Encapsulation: dot1q Operational Trunking Encapsulation: native Negotiation of Trunking: On Access Mode VLAN: 2 (switchlab99) Trunking Native Mode VLAN: 1 (default) --- output omitted ----

  42. Improving Performance with Spanning Tree Medium-Sized Switched Network Construction

  43. Advantages of EtherChannel • Logical aggregation of similar links between switches • Load-shares across links • Viewed as one logical port to STP • Redundancy

  44. Redundant Topology • Redundant topology eliminates single points of failure. • Redundant topology causes broadcast storms, multiple frame copies, and MAC address table instability problems.

  45. Broadcast Frames • Station D sends a broadcast frame. • Broadcast frames are flooded to all ports except the originating port.

  46. Multiple Frame Copies • Host X sends a unicast frame to router Y. • The MAC address of router Y has not been learned by either switch. • Router Y will receive two copies of the same frame.

  47. MAC Database Instability • Host X sends a unicast frame to router Y. • The MAC address of router Y has not been learned by either switch. • Switches A and B learn the MAC address of host X on port 1. • The frame to router Y is flooded. • Switches A and B incorrectly learn the MAC address of host X on port 2.

  48. Broadcast Storms • Host X sends a broadcast. • Switches continue to propagate broadcast traffic over and over.

  49. Loop Resolution with STP • Provides a loop-free redundant network topology by placing certain ports in the blocking state • Published in the IEEE 802.1D specification • Enhanced with the Cisco PVST+ implementation

  50. Spanning-Tree Operation • One root bridge per broadcast domain. • One root port per nonroot bridge. • One designated port per segment. • Nondesignated ports are unused.