1 © 2003, Cisco Systems, Inc. All rights reserved. CCNA 3 v3.0 Module 8 Virtual LANs

222 © 2003, Cisco Systems, Inc. All rights reserved. Objectives VLAN concepts VLAN configuration Troubleshooting VLANs

333 © 2003, Cisco Systems, Inc. All rights reserved. Introduction to VLANs

444 © 2003, Cisco Systems, Inc. All rights reserved. VLANs VLANs logically segment switched networks based on an organization's functions, project teams, or applications as opposed to a physical or geographical basis.

555 © 2003, Cisco Systems, Inc. All rights reserved. Broadcast Domains

666 © 2003, Cisco Systems, Inc. All rights reserved. Example with 3 Broadcast Domains, 3 VLANs

777 © 2003, Cisco Systems, Inc. All rights reserved. Static VLANs

888 © 2003, Cisco Systems, Inc. All rights reserved. Dynamic VLANs

999 © 2003, Cisco Systems, Inc. All rights reserved. Port-Centric VLANs

10 © 2003, Cisco Systems, Inc. All rights reserved. VLAN Configuration

11 © 2003, Cisco Systems, Inc. All rights reserved. Benefits of VLANs Easily move workstations on the LAN Easily add workstations to the LAN Easily change the LAN configuration Easily control network traffic Improve security

12 © 2003, Cisco Systems, Inc. All rights reserved. Communicating Between VLANs

13 © 2003, Cisco Systems, Inc. All rights reserved. VLAN Types

14 © 2003, Cisco Systems, Inc. All rights reserved. Inter-Switch Link

15 © 2003, Cisco Systems, Inc. All rights reserved. Concurrent Transmissions in a Switch

16 © 2003, Cisco Systems, Inc. All rights reserved. End-to-End VLANs VLAN membership for users is based on department or job function, regardless of where the users are located. All users in a VLAN should have the same 80/20 traffic flow patterns.

17 © 2003, Cisco Systems, Inc. All rights reserved. Static VLANs Static VLANs work well in networks where the following is true: Moves are controlled and managed. There is robust VLAN management software to configure the ports. It is not desirable to assume the additional overhead required when maintaining end- station MAC addresses and custom filtering tables.

18 © 2003, Cisco Systems, Inc. All rights reserved. Configuring Static VLANs When configuring VLAN on CAT2950 switches: Maximum number of VLANs is switch dependent. VLAN 1 is default Ethernet VLAN. CDP and VTP advertisements are sent on VLAN 1. CAT2950 IP address is in VLAN 1 broadcast domain by default. Switch must be in VTP server mode to create, add or delete VLANs.

19 © 2003, Cisco Systems, Inc. All rights reserved. Assign ports to the VLAN Switch(config)#interface fastethernet 0/9 Switch(config-if)#switchport access vlan vlan_number Create the VLAN: (This step is not required and will be discussed later.) Switch#vlan database Switch(vlan)#vlan vlan_number Switch(vlan)#exit Creating VLANs

20 © 2003, Cisco Systems, Inc. All rights reserved. Creating VLANs

21 © 2003, Cisco Systems, Inc. All rights reserved. Verifying VLAN Configuration

22 © 2003, Cisco Systems, Inc. All rights reserved. Saving VLAN Configuration Back up using the copy running-config tftp command, or you can use the HyperTerminal Capture Text feature to store the configuration settings.

23 © 2003, Cisco Systems, Inc. All rights reserved. Deleting VLANs The command below is used to remove a VLAN from a switch: Switch#vlan database Switch(vlan)#no vlan 300

24 © 2003, Cisco Systems, Inc. All rights reserved. VLAN Problem Isolation

25 © 2003, Cisco Systems, Inc. All rights reserved. Problem Isolation in Catalyst Networks 1.Check the physical indications, such as LED status. 2.Start with a single configuration on a switch and work outward. 3.Check the Layer 1 link. 4.Check the Layer 2 link. 5.Troubleshoot VLANs that span several switches.

26 © 2003, Cisco Systems, Inc. All rights reserved. Preventing Broadcast Storms If it becomes necessary to reduce BPDU traffic, put the timers on the root bridge at their maximum values. Specifically, set the forward delay parameter to the maximum of 30 seconds, and set the max_age parameter to the maximum of 40 seconds.

27 © 2003, Cisco Systems, Inc. All rights reserved. Common Problems in Troubleshooting VLANs

28 © 2003, Cisco Systems, Inc. All rights reserved. Catalyst IOS show vlan Command

29 © 2003, Cisco Systems, Inc. All rights reserved. Catalyst IOS Keyword Syntax Description

30 © 2003, Cisco Systems, Inc. All rights reserved. Catalyst IOS show spanning-tree Command

31 © 2003, Cisco Systems, Inc. All rights reserved. VLAN Troubleshooting Scenarios A trunk link cannot be established between a switch and a router 1.Make sure that the port is connected and not receiving any physical-layer, alignment or frame- check-sequence (FCS) errors. This can be done with the show interfaces command on the switch. 2.Verify that the duplex and speed are set properly between the switch and the router. This can be done with the show interface status command on the switch or the show interfaces command on the router. 3.Configure the physical router interface with one subinterface for each VLAN that will route traffic. Verify this with the show interfaces IOS command. Also, make sure that each subinterface on the router has the proper encapsulation type, VLAN number, IP address, and subnet mask configured. This can be done with the show interfaces or show running-config IOS commands. 4.Confirm that the router is running an IOS release that supports trunking. This can be verified with the show version command.

32 © 2003, Cisco Systems, Inc. All rights reserved. VLAN Troubleshooting Scenarios Dropped packets and loops In this scenario, Switch A, Switch B, and Switch C are running the IEEE spanning-tree algorithm. Switch D is inadvertently configured to use the DEC spanning-tree algorithm. Switch A claims to be the IEEE root and Switch D claims to be the DEC root. Switch B and Switch C propagate root information on all interfaces for IEEE spanning tree. However, Switch D drops IEEE spanning-tree information. Similarly, the other routers ignore Router D's claim to be root. The result is that in none of the bridges believing there is a loop and when a broadcast packet is sent on the network, a broadcast storm results over the entire internetwork. This broadcast storm will include Switches X and Y, and beyond. To resolve this problem, reconfigure Switch D for IEEE. Although a configuration change is necessary, it might not be sufficient to reestablish connectivity. There will be a reconvergence delay as devices exchange BPDUs and recompute a spanning tree for the network.