CIT 384: Network AdministrationSlide #1 CIT 384: Network Administration VLANs

CIT 384: Network AdministrationSlide #2 Topics 1.What is a VLAN? 2.VLAN Tagging 3.Subnets 4.VTP 5.IOS VLAN Commands

CIT 384: Network AdministrationSlide #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 AdministrationSlide #4 Why use VLANs? 1.Organize the network logically instead of by which hosts are plugged into which switch. 2.Reduce size of broadcast domains to reduce broadcast overhead. 3.To enforce security by restricting sensitive hosts to specific VLANs. 4.To reduce workload of STP. 5.Separate VoIP from data traffic.

CIT 384: Network AdministrationSlide #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 AdministrationSlide #6 VLAN Trunking

CIT 384: Network AdministrationSlide #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 AdministrationSlide #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 AdministrationSlide #9 VLAN IDs 12-bit number between –Lowest and highest VLAN IDs excluded. –Normal range: –Extended range:

CIT 384: Network AdministrationSlide #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 AdministrationSlide #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 AdministrationSlide #12 Subnets and VLANs

CIT 384: Network AdministrationSlide #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 AdministrationSlide #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 AdministrationSlide #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 AdministrationSlide #16 VTP Updates

CIT 384: Network AdministrationSlide #17 VTP Requirements 1.Switches must be connected using a VLAN trunk. 2.Switches must share the same case- sensitive VTP domain name. 3.If a password is configured, switches must share case-sensitive VTP password.

CIT 384: Network AdministrationSlide #18 VTP Pruning (for VLAN 10)

CIT 384: Network AdministrationSlide #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 AdministrationSlide #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 AdministrationSlide #21 VLAN Configuration Example

CIT 384: Network AdministrationSlide #22 VLAN Configuration Example

CIT 384: Network AdministrationSlide #23 VLAN Configuration Example

CIT 384: Network AdministrationSlide #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 AdministrationSlide #25 References 1.James Boney, Cisco IOS in a Nutshell, 2 nd edition, O’Reilly, Cisco, Cisco Connection Documentation, Cisco, Internetworking Basics, k/ito_doc/introint.htm k/ito_doc/introint.htm 4.Matthew Gast, Wireless Networks: The Definitive Guide, O’Reilly, Wendell Odom, CCNA Official Exam Certification Library, 3 rd edition, Cisco Press, 2007.