Switching Layer 2 Switching By: Mohand For: arabhardware

Low cost and latency Switching limitations: .Must break up collision domains correctly .Wire speed .Cost – effective – resilient internetworking Switching services: .address learning: enter this info into a MAC database - Station A sends a frame to station C Switch caches the MAC address of station A to port E0 by learning the source address of data frames ‎ The frame from station A to station C is flooded out to all ports except port E0‎ Forward/filter decisions - Station A sends a frame to station C Destination is know : frame is not flooded .Switching Layer 2 Switching Purposes for using switching: .Both make forwarding decisions based on layer 1 address Switching functions at layer 2: .Make sure that users spend 80 percent of their time on the local segment .Switches do not break broadcast domains by default Bridging VS.Hardware – based bridging (ASIC) . LAN Switching: Bridge Switch Software based Hardware based ASIC chips Have one STP per bridge Have many Low number of ports Many numbers of ports .Breaks up collision domains .

multiple frame copies and MAC Database instability Common Spanning-tree protocol: Used to make the switches communicate Prevent redundant paths Prevent loops Create from the block path a backup . STP used to stop network loops Redundant topology: - - - Redundant topology: eliminates single points of failure Redundant topology causes: broadcast storms .- Station A sends a frame to station B The switch has the address for station B in the MAC address table Loop avoidance: if multiple connections between the switches are created for redundancy network loops can occur .

Disable: by administrator manually VLAN'S: A logical grouping of network users and resources connected to administratively ports on a switch VLANs Features: .Blocking 20 seconds .Flexibility and scalability .Bridge id = bridge priority (2byte) |Mac address (6byte) .If equal  the lowest bridge id .Listening 15 seconds .Non designated port unused Spanning-tree path cost: Link speed 10 Gbps 1 Gbps 100 Mbps 10 Mbps Cost by IEEE 2 4 19 100 Root Bridge: (DF) .Operation: .All ports at the root bridge are designated forward Root port: (RF) .Learning 15 seconds .The lowest cost to root bridge .If equal  the lowest bridge id .One root bridge per network .If equal  the low port number Spanning-tree port state: .Root bridge = bridge with lowest bridge id .One root port per non root bridge .Forwarding .One designated port per segment .The lowest cost to root bridge .Provides a level of security over a flat network .Simplify network management (Segmentation) .If equal  the low port number Designated port: (DF) .BPDU : bridge protocol data unit .

Inter-switch link (ISL) : Cisco proprietary | Fast Ethernet & Giga Ethernet only .Dynamic VLAN's : automatic  (VMPS) VLAN management policy server VLAN Identifying: .Truck links : carries multiple VLANs Frame Tagging: .VLAN Operation: - Each logical VLAN is like a separate physical bridge VLANS can span across multiple switches Trunks carry traffic for multiple VLANS Trunks use special encapsulation distinguish between different VLANs VLAN Memberships: .Static VLANs : typical and most secure .Access links : a link that is part of only one VLAN .IEEE 802.1Q Trucking : used for Cisco and non-Cisco switch VLAN 1 native VLAN untagged traffic (Save size for another application like voip) .

VTP advertisements are sent every 5 minutes or when there is a change . delete and rename VLANs VTP Modes: VTP Operation: .VTP advertisements are sent as multicast frames .Per-VLAN Spanning-Tree: VLAN Trunking protocol: (VTP) Manage all configuration VLANs.VTP servers and clients are synchronized to the latest revision number . allow an administrator to add.

When a change is made to the VLAN database. . it is propagated to all switches via VTP advertisements. Cisco alway s “thinks big” to create a method for you to just sit at the “Main Sw”. right? It is not a dream. Your technical colleagues can sit anywhere on the floors to access Technical VLAN (VLAN 4). such as duplicate VLAN names or incorrect VLAN-type specifications. other switches automatically learn about this VLAN. they need to be configured in the same VTP domain. Now let’s discuss about VTP role in this topology! Suppose VTP is not running on these switches. sweet. your boss decides to add a new department to your office. Suppose you are working in a medium company in a 5-floor office. it will surely become a daunting task to add a new VLAN like this. To help you understand the basic concept.This topic describes the features that VLAN Trunking Protocol (VTP) offers to support VLANs. This is the best design because each person’s permission is not limited by the physica l location. You assigned each floor to a switch for easy management and of course they can be assigned to different VLANs. adding your new VLANs and magically. it is what VTP does for you! How VTP Works To make switches exchange their VLAN information with each other. this is a summary of what VTP is: “VTP allows a network manager to configure a switch so that it will propagate VLAN configurations to other switches in the network” VTP minimizes misconfigurations and configuration inconsistencies that can cause problems. Only switches belonging to the same domain share their VLAN information. For example. Fortunately your office only has 5 floors so you can finish this task in some hours :) But just imagine if your company was bigger with 100-floor office and some VLANs needed to be added every month! Well. How will you do that? Well. without VTP you have to go to each switch to enable this new VLAN. VTP helps you simplify management of the VLAN database across multiple switches. let’s discuss a real and popular network topology. Why we need VTP? To answer this question. your bosses can sit in any floor and still access Manage VLAN (VLAN 7). Luckily. VTP is a Cisco-proprietary protocol and is available on most of the Cisco switches. One day. and you are tasked to add a new SUPPORT VLAN for this department. the Support Department.

Now return to the example above. we can configure any switches as the “server” but for our convenience. Client switches first . the “Main Sw” should be assigned this function and we should place it in a safe place. For example. So the higher the revision number. They are operated in Client mode. In some cases. This is also the default mode. the configuration revision is incremented by one. This switch is like the “master” of the whole VTP domain and it is operated in Server mode. This number is used in order to determine whether the VTP advertisement is more recent than the current version of that switch. it will send a VTP advertisement with the Revision number of 2. only one switch should be allowed to create (or delete. Other switches are only allowed to receive and forward updates from the “server” switch. He can set it toTransparent mode. modify) new VLAN. the first time the Main Sw sends a VTP advertisement.To maintain domain consistency. VTP advertisements bring VLAN information to all the switches in a VTP domain. In this mode. Because each time you make a VLAN change in a switch. its Revision number is 1. it still forwards VTP advertisements from the server to other switches (but doesn’t read that update). A transparent switch can add. When you add a new VLAN to the Main Sw. the network manager doesn’t want a switch to learn VTP information from other switches. As said above. Each VTP advertisement is sent with a Revision number. the better your VTP advertisement. a switch maintains its own VLAN database and never learn VTP information from other switches (even the server). delete and modify VLAN database locally. However.

client. By default. + VTP V2 Mode: displays if VTP version 2 mode is enabled. The “show vtp status” command analysis The most important command to view the status of VTP on Cisco switches that each CCNA learners must grasp is the “show vtp status” command. it deletes its whole VTP information and copy the new information from the better VTP advertisement to its VLAN database. Let’s have a look at the output of this command: + VTP Version: displays the VTP version the switch is running. + Maximum VLANs Supported Locally: maximum number of VLANs supported locally. + Configuration Revision: current Revision number on this switch. + MD5 Digest: a 16-byte checksum of the VTP configuration. it continues comparing with its current Revision number (1) -> it continues update its VLAN database. a switch operates in VTP Server mode with a NULL (blank) domain name with no password configured (the password field is not listed in the output) + VTP Pruning Mode: displays whether pruning is enabled or disabled. + VTP Domain Name: name that identifies the administrative domain for the switch. Next it receives the VTP advertisement with the Revision number of 2. We will discuss about VTP Pruning later. + VTP Operating Mode: can be server. By default. VTP version 2 is disabled by default. Displays the IP address of the switch that caused the configuration change to the database. One important thing you must know is when a switch receives a better VTP advertisement. which is bigger than its current Revision number (0) so it updates its VLAN database. + Number of Existing VLANs: Number of existing VLANs.receive the VTP advertisement with the Revision number of 1. the switch runs version 1 but can be set to version 2. the two VTP versions are not interoperable so make sure to configure the same VTP version on every switch in a domain. Within a domain. or transparent. + Configuration Last Modified: date and time of the last configuration modification. A switch does not try to compare its own VLAN database with information from the received VTP advertisements to find out and update the difference! Note: VTP advertisements are sent as multicast frames and all neighbors in that domain receive the frames. . + VTP Traps Generation: displays whether VTP traps are sent to a network management station.

VTP Pruning makes more efficient use of trunk bandwidth by forwarding broadcast and unknown unicast frames on a VLAN only if the switch on the receiving end of the trunk has ports in that VLAN. and Sw3 all receive broadcast frames from PC A. let’s see an example: When PC A sends a broadcast frame on VLAN 10. Sw2. For example. the switch sends an advertisement to its neighbors to inform that it has active ports on that VLAN.VTP Pruning: Increases available bandwidth by reducing unnecessary flooded traffic To understand what VTP Pruning is. Server switch doesn’t send broadcast frame to Sw2 because Sw2 doesn’t have ports in VLAN 10. Switches Server. Moreover. The link between switches Server and Sw2 does not carry any VLAN 10 traffic so it can be “pruned”. But only Sw3 has user on VLAN 10 and it is a waste of bandwidth on Sw2. that broadcast traffic also consumes processor time on Sw2. In the above example. Sw3 sends an advertisement to Server switch to inform that it . When a switch has a port associated with a VLAN. it travels across all trunk links in the VTP domain.

the VTP server increments its configuration revision number and then advertises the new revision throughout the VTP domain via VTP advertisements. the change affects only the local switch and does not propagate to other switches in the VTP domain. In Server mode we can create. however. Your trunk link can automatically be formed if both of your switches are not 2960 or 3560 because ports on the 2960 and 3560 switches are set to dynamic auto by default. To configure trunk between these ports. the link will remain in access mode. delete VLANs. VTP client also forwards VTP advertisements (but cannot create VTP advertisements). VTP transparent mode does forward VTP advertisements that it receives within the domain. VTP modes: * Server: The default mode. + VTP operates in one of three modes: server. You only need to enable pruning on one VTP server switch in the domain. modify. or client. the change is propagated to all switches in the VTP domain. * Client: cannot make changes to the VLAN configuration when in this mode. VTP messages are transmitted out of all the trunk connections. VTP Pruning makes more efficient use of trunk bandwidth by forwarding broadcast and unknown unicast frames on a VLAN only if the switch on the receiving end of the trunk has ports in that VLAN . * Transparent: When you make a change to the VLAN configuration in this mode. When you make a change to the VLAN configuration on a VTP server. transparent. a VTP client can send any VLANs currently listed in its database to other VTP switches. VTP Configuration Main Main Main Main Sw(config)#vtp Sw(config)#vtp Sw(config)#vtp Sw(config)#vtp version 2 domain 9tut mode server password keepitsecret On client switches Client(config)#vtp Client(config)#vtp Client(config)#vtp Client(config)#vtp version 2 domain 9tut password keepitsecret mode client Notice: Before configuring VTP make sure the links between your switches are trunk links. Sw2 has not advertised about VLAN 10 so Server switch will prune VLAN 10 on the trunk to Sw2. Below summaries important notes about VTP: + Whenever a change occurs in the VLAN database. use these commands: Client(config)#interface fa0/1 (or the interface on the link you want to be trunk) Client(config-if)#switchport mode trunk These commands only need to be used on one of two switches to form the trunk.has active port for VLAN 10. If both sides are set to dynamic auto.