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CIT 384: Network Administration

CIT 384: Network Administration. VLANs. Topics. What is a VLAN? VLAN Tagging Subnets VTP IOS VLAN Commands. What is a VLAN?. A LAN consists of all the hosts in a single broadcast domain. A VLAN is the same. Without VLANs, all ports on a switch belong to the same LAN.

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CIT 384: Network Administration

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  1. CIT 384: Network Administration VLANs CIT 384: Network Administration

  2. Topics • What is a VLAN? • VLAN Tagging • Subnets • VTP • IOS VLAN Commands CIT 384: Network Administration

  3. What is a VLAN? • A LAN consists of all the hosts in a single broadcast domain. • A VLAN is the same. • Without VLANs, all ports on a switch belong to the same LAN. • With VLANs, a switch can support one broadcast domain per VLAN. CIT 384: Network Administration

  4. Why use VLANs? • Organize the network logically instead of by which hosts are plugged into which switch. • Reduce size of broadcast domains to reduce broadcast overhead. • To enforce security by restricting sensitive hosts to specific VLANs. • To reduce workload of STP. • Separate VoIP from data traffic. CIT 384: Network Administration

  5. VLANs can span switches • A LAN spans multiple connected switches unless there is a router between switches. • A VLAN needs extra data to span switches • VLAN ID identifies the VLAN. • Packets are tagged with a header containing VLAN ID so that recipient switch knows which VLAN packet is for. CIT 384: Network Administration

  6. VLAN Trunking CIT 384: Network Administration

  7. VLAN Trunking Protocols ISL: Cisco proprietary VLAN protocol • Ethernet frame encapsulated in ISL. • ISL header contains source and destination MAC addresses of the two switches. CIT 384: Network Administration

  8. VLAN Trunking Protocols 802.1Q: IEEE standard VLAN protocol. • Inserts 32-bit tag into Ethernet header. • Requires FCS to be recalculated. CIT 384: Network Administration

  9. VLAN IDs 12-bit number between 1-4094 • Lowest and highest VLAN IDs excluded. • Normal range: 1-1005 • Extended range: 1006-4094 CIT 384: Network Administration

  10. Native VLAN 802.1Q supports one native VLAN per trunk. • Native VLAN is VLAN 1 by default. • Native VLAN packets are not tagged. • Helps support switches that do not understand VLAN tagging. CIT 384: Network Administration

  11. Subnets and VLANs • Hosts on a single VLAN must be on the same IP subnet. • Hosts on different VLANs must be on different IP subnets. • For hosts on two different VLANs to communicate, a router is needed even if the hosts are plugged into the same switch. CIT 384: Network Administration

  12. Subnets and VLANs CIT 384: Network Administration

  13. VTP: VLAN Trunking Protocol • Manual configuration requires creating a VLAN individually on each switch. • VTP will transmit VLAN configuration information from one switch to all other switches using VTP. • VPT messages sent on configuration change and once every 5 minutes. • Similar to a routing protocol. CIT 384: Network Administration

  14. VTP Modes Server Mode • Accepts VLAN configuration. • Sends and receives VTP udpates. Client Mode • Receives VTP updates. Transparent Mode • Ignores VTP updates. CIT 384: Network Administration

  15. VTP Updates • Updates are processes only if VLAN configuration database number in update is higher than current configuration number. • Each time VLAN configuration is updated, server increments VLAN config number. • Good practice t CIT 384: Network Administration

  16. VTP Updates CIT 384: Network Administration

  17. VTP Requirements • Switches must be connected using a VLAN trunk. • Switches must share the same case-sensitive VTP domain name. • If a password is configured, switches must share case-sensitive VTP password. CIT 384: Network Administration

  18. VTP Pruning (for VLAN 10) CIT 384: Network Administration

  19. VLAN Configuration DB VLAN configuration database • Not stored in running-config. • Stored in vlan.dat file in flash RAM. • Use show commands to access. CIT 384: Network Administration

  20. Creating a VLAN Configure new VLAN (config)# vlan vlan-id (config-vlan)# name vlan-name Configure interfaces for VLAN (config)# interface name (config-if)# switchport access vlan vlan-id CIT 384: Network Administration

  21. VLAN Configuration Example CIT 384: Network Administration

  22. VLAN Configuration Example CIT 384: Network Administration

  23. VLAN Configuration Example CIT 384: Network Administration

  24. Protecting unused switch ports Administratively disable unused ports. shutdown Prevent trunking from being negotiated. switchport nonegotiate Assign port to unused VLAN. switchport access vlan vlan-id CIT 384: Network Administration

  25. References • James Boney, Cisco IOS in a Nutshell, 2nd edition, O’Reilly, 2005. • 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 • Matthew Gast, 802.11 Wireless Networks: The Definitive Guide, O’Reilly, 2005. • Wendell Odom, CCNA Official Exam Certification Library, 3rd edition, Cisco Press, 2007. CIT 384: Network Administration

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