reaches that point, the counter will reset back to
zero. There are two types of VTP advertisements:
- Requests from clients that want information at bootup
- Response from servers
There are three types of
VTP messages: - Advertisement requests
- Summary
advertisements
- Subset advertisements
With
advertisement requests, clients request VLAN information and
the server responds with summary and subset advertisements. By
default, server and client Catalyst switches issue summary
advertisements every five minutes. Servers inform neighbor
switches what they believe to be the current VTP revision
number. Assuming the domain names match, the receiving server
or client compares the configuration revision number. If the
revision number in the advertisement is higher than the current
revision number in the receiving switch, the receiving switch
then issues an advertisement request for new VLAN information.
Subset advertisements contain detailed information about VLANs
such as VTP version type, domain name and related fields, and
the configuration revision number. The following can trigger
these advertisements: - Creating or deleting a
VLAN
- Suspending or activating a VLAN
- Changing
the name of a VLAN
- Changing the maximum transmission
unit (MTU) of a VLAN
Advertisements may contain
some or all of the following information: - Management
domain name. Advertisements with different names are ignored.
- Configuration revision number. The higher number
indicates a more recent configuration.
- Message Digest
5 (MD5). MD5 is the key that is sent with the VTP when a
password has been assigned. If the key does not match, the
update is ignored.
- Updater identity. The updater
identity is the identity of the switch that is sending the VTP
summary advertisement.
Web Links
Understanding and Configuring VLAN Trunk Protocol (VTP)
http://www.cisco.com/en/US/tech/
tk389/tk689/technologies_tech_note
09186a0080094c52.shtml
Content 9.2 VTP 9.2.5 VTP
configuration The following basic tasks must be considered
before configuring VTP and VLANs on the network.
- Determine the version number of VTP that will be
utilized.
- Decide if this switch is to be a member of
an existing management domain or if a new domain should be
created. If a management domain exists, determine the name and
password of the domain.
- Choose a VTP mode for the
switch.
Two different versions of VTP are
available, Version 1 and Version 2. The two versions are not
interoperable. If a switch is configured in a domain for VTP
Version 2, all switches in the management domain must be
configured for VTP Version 2. VTP Version 1 is the default. VTP
Version 2 may be implemented if some of the specific features
that VTP Version 2 offers are not offered in VTP Version 1. The
most common feature that is needed is Token Ring VLAN support.
To configure the VTP version on a Cisco IOS command-based
switch, first enter VLAN database mode. Use the following
command to change the VTP version number on a set command-based
switch. Switch#vlan database
Switch(vlan)#vtp
v2-mode If the switch being installed is the first switch
in the network, create the management domain. If the management
domain has been secured, configure a password for the domain.
To create a management domain use the following command:
Switch(vlan)#vtp domain cisco The domain name can be
between 1 and 32 characters. The password must be between 8 and
64 characters long. To add a VTP client to an existing VTP
domain, always verify that its VTP configuration revision
number is lower than the configuration revision number of the
other switches in the VTP domain. Use the show vtp
status command. Switches in a VTP domain always use the
VLAN configuration of the switch with the highest VTP
configuration revision number. If a switch is added that has a
revision number higher than the revision number in the VTP
domain, it can erase all VLAN information from the VTP server
and VTP domain. Choose one of the three available VTP modes for
the switch. If this is the first switch in the management
domain and additional switches will be added, set the mode to
server. The additional switches will be able to learn VLAN
information from this switch. There should be at least one
server. VLANs can be created, deleted, and renamed at will
without the switch propagating changes to other switches. If a
large number of people are configuring devices within the
network, there is a risk of overlapping VLANs with two
different meanings in the network but with the same VLAN
identification. To set the correct mode of the Cisco IOS
command-based switch, use the following command:
Switch(vlan)#vtp {client | server | transparent} Figure
shows the output of the show vtp status command. This
command is used to verify VTP configuration settings on a Cisco
IOS command-based switch. Figure shows an example of the
show vtp counters command. This command is used to
display statistics about advertisements sent and received on
the switch. Lab Activity Lab Exercise: VTP Client and
Server Configurations This lab is to configure the VTP protocol
to establish server and client switches . Lab Activity
e-Lab Activity: VTP Client and Server Configurations In this
lab, the student will configure the VTP protocol to establish
server and client switches . Web Links Multilayer
Switching Commands http://www.cisco.com/univercd/cc/
td/doc/product/software/ios120/12cgcr/
switch_r/xrmls.htm
Content 9.3 Inter-VLAN Routing
Overview 9.3.1 VLAN basics A VLAN is a logical grouping
of devices or users that can be grouped by function,
department, or application regardless of their physical
location. VLANs are configured at the switch through software.
The number of competing VLAN implementations can require the
use of proprietary software from the switch vendor. Grouping
ports and users into communities of interest, referred to as
VLAN organizations, may be accomplished by the use of a single
switch or more powerfully among connected switches within the
enterprise. By grouping the ports and users together across
multiple switches, VLANs can span single building
infrastructures or interconnected buildings. VLANs assist in
the effective use of bandwidth as they share the same broadcast
domain or Layer 3 network. VLANs optimize the collection and
use of bandwidth. VLANs contend for the same bandwidth although
the bandwidth requirements may vary greatly by workgroup or
department. The following are some VLAN configuration issues:
- A switch creates a broadcast domain
- VLANs
help manage broadcast domains
- VLANs can be defined on
port groups, users or protocols
- LAN switches and
network management software provide a mechanism to create
VLANs
VLANs help control the size of broadcast
domains and localize traffic. VLANs are associated with
individual networks. Therefore, network devices in different
VLANs cannot directly communicate without the intervention of a
Layer 3 routing device. When a node in one VLAN needs to
communicate with a node in another VLAN, a router is necessary
to route the traffic between VLANs. Without the routing device,
inter-VLAN traffic would not be possible.
Content
9.3 Inter-VLAN Routing Overview
9.3.2 Introducing inter-VLAN routing When a host in one
broadcast domain wishes to communicate with a host in another
broadcast domain, a router must be involved. Port 1 on a switch
is part of VLAN 1, and port 2 is part of VLAN 200. If all of
the switch ports were part of VLAN 1, the hosts connected to
these ports could communicate. In this case however, the ports
are part of different VLANs, VLAN 1 and VLAN 200. A router must
be involved if hosts from the different VLANs need to
communicate. The most important benefit of routing is its
proven history of facilitating networks, particularly large