Trunk
·
A switch port that can
carry multiple traffic types, each tagged with a unique VLAN ID.
Switchport
·
Command (only required
on Layer 3-capable or Multilayer switches) that configures the desired
interface as a Layer 2 switch port.
DISL (Dynamic Inter-Switch
Link Protocol)
·
Simplifies the
creation of an ISL trunk from two interconnected FastEthernet devices.
Minimizes VLAN trunk configuration procedures because only one end of a link
needs to be configured as a trunk.
DTP (Dynamic Trunking
Protocol)
·
Cisco proprietary
point-to-point protocol that negotiates a common trunking mode between two
switches. This dynamic negotiation can also include trunking encapsulation. The
two modes of DTP which a switch port can use are Dynamic Desirable and Dynamic
Auto.
switchport mode trunk
·
Interface
configuration command that forces the port into a permanent (static) trunking
mode. Although this configuration of a trunk link forces the switch to
establish a trunk, Dynamic ISL and DTP packets will still be sent out of the
interface.
show interfaces
[interface#] switchport
·
Shows the
configuration of a trunk link.
switchport nonegotiate
·
Interface
configuration command that allows you to disable the sending of DISL and DTP
packets.
Dynamic Desirable (DTP
Mode)
·
The port will actively
attempt to become a trunk.
Dynamic Auto (DTP
Mode)
·
The port will revert
to being a trunk only if the neighboring switch port is set to Dynamic
Desirable mode.
show DTP
·
Command that shows DTP
information globally for the switch or for the specified hardware.
show dtp interface
[name]
·
Command that prints
DTP information about the specified interfae, which includes the type of
interface (trunk or access), the current port DTP configuration, the trunk
encapsulation, and DTP packet statistics.
VLAN1
·
A VLAN used by the
switch to carry specific protocol traffic, like CDP, VTP, PAgp, and DTP
information.
switchport trunk
native vlan [number]
·
Interface
configuration mode command that allows you to change the native VLAN.
Inter-VLAN Routing
·
Routing traffic
between different VLANs. The three methods of accomplishing this are: using
physical router interfaces, using router subinterfaces, using switched virtual
interfaces (SVIs)
Physical Router
Interfaces (Inter-VLAN Routing)
·
If you use a router
with multiple physical interfaces as the default gateway for each individually
configured VLAN, then you can route packets received from one VLAN to another
using these physical LAN interfaces. Not a scalable solution due to the
required physical interfaces. Each physical interface is configured as an
access link in the desired VLAN; the physical interfaces are then configured
with the appropriate IP addresses. This type of Inter-VLAN Routing is also
known as "Router-on-a-Stick." The only problem is that the routers
bandwidth is being shared between all of the various VLANs on the
subinterfaces, and thus the router can become a bottleneck.
Router Subinterfaces
(Inter-VLAN Routing)
·
Only a single physical
interface is required to setup this type of inter-VLAN routing. Subinterfaces
are configured using the main physical router interface. Ensure that you've
assigned an IP address to the interface. The link connected to the physical interface
must be configured as a trunk link because routers don't support DTP.
interface [name]
[subinterface number]
·
Global Configuration
command that allows you to assign a subinterface to a physical interface.
encapsulation [isl |
dot1Q] [vlan]
·
Subinterface
configuration command that allows you to associate a subinterface with a
particular VLAN.
Switched Virtual
Interfaces (Inter-VLAN Routing)
·
Not a Layer 2 VLAN,
but a way for Inter-VLAN Routing to occur by assigning and IP address to this
and creating a logical interface. Also the most recommended Inter-VLAN Routing
solution when using multilayer switches.
show sdm prefer
·
Global Configuration
mode command that shows the preferences for Switch Database Management. To
configure Inter-VLAN Routing on a Cisco switch you must have lanbase-routing
enabled.
VTP (VLAN Trunking
Protocol)
·
A Cisco proprietary
Layer 2 messaging protocol that manages the addition, deletion, and renaming of
VLANS on switches in the same kind of this domain. This protocol allows VLAN
information to propagate through the switched network, which reduces
administration overhead in a switched network, whilst enabling switched to
exchange and maintain consistent VLAN information.
vtp mode <Server,
Client, Transparent>
·
Global Configuration
mode command that sets the vtp mode.
vtp domain [name]
·
Global Configuration
mode command that sets the name of a vtp domain.
vtp password
[password]
·
Global Configuration
mode command that sets the password of a vtp domain.
Server (VTP Mode)
·
The switch is
authorized to create, modify, and delete VLAN information for the entire VTP
domain. Any changes you make to a server are propagated throughout the whole
domain.
Client (VTP Mode)
·
The switch will
receive VTP information and apply any changes, but it does not allow adding,
removing, or changing VLAN information on the switch. The client will also send
the VTP packet received out of its trunk ports. Remember that you cannot add a
swith port on a VTP client switch to a VLAN that does not exist on the VTP
server.
Transparent (VTP Mode)
·
The switch will
forward the VTP information received out of its trunk ports, but it will not
apply the changes. This VTP mode can create, modify, and delete VLANs, but the
changes are not propagated to other switches. This mode is needed to configure
the extended VLAN range (1006 - 4096).
VTP Pruning
·
Switches can use this
method to prune unnecessary VLAN information on switches to reduce broadcast
traffic. The problem is that if there's a switch set to transparent mode
in-between two switches, then pruning will not work.
vtp pruning
·
Global Configuration
command that adds VTP pruning to your switch.
Configuration Revision
Number
·
A 32-bit number that
indicates the level of revision for a VTP packet. This information is used to
determine whether t he received information is more recent than the current
version. Each time that you make a VLAN change on a switch in VTP server mode,
the configuration revision is incremented by one and change will be propagated
to VTP clients (switches in VTP transparent mode will have a revision number of
0 and will not increase when the database changes).
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