Switching Layer 2 Switching By: Mohand For: arabhardware

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 .Low cost and latency Switching limitations: .Wire speed . 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 .Must break up collision domains correctly .Hardware – based bridging (ASIC) .Switching Layer 2 Switching Purposes for using switching: .Both make forwarding decisions based on layer 1 address Switching functions at layer 2: .Cost – effective – resilient internetworking Switching services: .Switches do not break broadcast domains by default Bridging VS.Breaks up collision domains .Make sure that users spend 80 percent of their time on the local segment .

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 .- 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 . STP used to stop network loops Redundant topology: - - - Redundant topology: eliminates single points of failure Redundant topology causes: broadcast storms .

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

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: .Truck links : carries multiple VLANs Frame Tagging: .1Q Trucking : used for Cisco and non-Cisco switch VLAN 1 native VLAN untagged traffic (Save size for another application like voip) .Dynamic VLAN's : automatic  (VMPS) VLAN management policy server VLAN Identifying: .IEEE 802.Inter-switch link (ISL) : Cisco proprietary | Fast Ethernet & Giga Ethernet only .Access links : a link that is part of only one VLAN .Static VLANs : typical and most secure .

VTP servers and clients are synchronized to the latest revision number . 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 advertisements are sent every 5 minutes or when there is a change . allow an administrator to add.

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

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

+ Maximum VLANs Supported Locally: maximum number of VLANs supported locally. We will discuss about VTP Pruning later. One important thing you must know is when a switch receives a better VTP advertisement. Let’s have a look at the output of this command: + VTP Version: displays the VTP version the switch is running. + VTP Domain Name: name that identifies the administrative domain for the switch. it continues comparing with its current Revision number (1) -> it continues update its VLAN database. Displays the IP address of the switch that caused the configuration change to the database. or transparent. VTP version 2 is disabled by default. + VTP V2 Mode: displays if VTP version 2 mode is enabled. 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 Operating Mode: can be server. it deletes its whole VTP information and copy the new information from the better VTP advertisement to its VLAN database. Within a domain. the switch runs version 1 but can be set to version 2.receive the VTP advertisement with the Revision number of 1. which is bigger than its current Revision number (0) so it updates its VLAN database. By default. + Number of Existing VLANs: Number of existing VLANs. By default. + VTP Traps Generation: displays whether VTP traps are sent to a network management station. + Configuration Revision: current Revision number on this switch. . + Configuration Last Modified: date and time of the last configuration modification. 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. client. the two VTP versions are not interoperable so make sure to configure the same VTP version on every switch in a domain. + MD5 Digest: a 16-byte checksum of the VTP configuration. Next it receives the VTP advertisement with the Revision number of 2. 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.

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

however. the VTP server increments its configuration revision number and then advertises the new revision throughout the VTP domain via VTP advertisements. 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. a VTP client can send any VLANs currently listed in its database to other VTP switches. 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. modify. If both sides are set to dynamic auto. * Client: cannot make changes to the VLAN configuration when in this mode. 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. * Transparent: When you make a change to the VLAN configuration in this mode. delete VLANs. In Server mode we can create. the change is propagated to all switches in the VTP domain. or client. VTP modes: * Server: The default mode. To configure trunk between these ports. 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 . + VTP operates in one of three modes: server. VTP messages are transmitted out of all the trunk connections. VTP transparent mode does forward VTP advertisements that it receives within the domain. Sw2 has not advertised about VLAN 10 so Server switch will prune VLAN 10 on the trunk to Sw2. You only need to enable pruning on one VTP server switch in the domain. transparent. the link will remain in access mode.has active port for VLAN 10. VTP client also forwards VTP advertisements (but cannot create VTP advertisements). When you make a change to the VLAN configuration on a VTP server. the change affects only the local switch and does not propagate to other switches in the VTP domain.