virtual access GW Series Instruction sheet

Configuring VLAN and CDP on a
GW Series Router
Issue
1.4
Date
10 May 2012

Table of contents
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company.
Configuring VLAN and CDP on a GW Series Router
Issue 1.4 Page 2 of 12
1About this document ............................................................................... 3
1.1 Scope ..................................................................................................... 3
1.2 Readership ............................................................................................. 3
1.3 Terminology ........................................................................................... 3
2Introduction to VLAN............................................................................... 4
2.1 Configuring the router for VLAN ............................................................. 4
2.2 Configuring an individual interface for VLAN .......................................... 5
2.3 Viewing VLAN tags ................................................................................. 6
2.4 Deployment scenario example ............................................................... 7
2.5 Debugging VLAN .................................................................................... 8
3CDP ....................................................................................................... 10
3.1 Configuring the router for CDP ............................................................. 10
3.2 CDP flows ............................................................................................. 11
3.3 Debugging CDP .................................................................................... 11
3.3.1 Tracing using the command line ..............................................................11

1: About this document
Configuring VLAN and CDP on a GW Series Router
Issue 1.4 Page 3 of 12
© 2012 Virtual Access.
1About this document
1.1 Scope
This configuration guide explains:
how to set up and configure VLAN and CDP on a GW Series router; and
the basic functionality of VLAN and CDP on a GW Series router.
1.2 Readership
This document is for engineers who have previous experience configuring and managing
Virtual Access routers.
1.3 Terminology
CDP
Cisco Discovery Protocol
QoS
Quality of Service
VLAN
Virtual Local Area Network
VoIP
Voice over Internet Protocol

2: Introduction to VLAN
Configuring VLAN and CDP on a GW Series Router
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© 2012 Virtual Access.
2Introduction to VLAN
Virtual Access routers support 802.1Q tagged-based VLAN. Tagging is the process of
adding a 4 byte tag containing the VID (VLAN ID) to an Ethernet frame.
Hosts send traffic with or without a VLAN tag. The Virtual Access router assigns this
traffic to a particular Ethernet port based on the 802.1Q tag.
VLANs can be used to group hosts together as if they exist physically on the same wire or
alternatively, hosts that are already physically on the same wire can be logically
separated.
VLANs are used to allow different logical networks to be connected to the same physical
hardware without any cross-leakage of data from one VLAN to any other at layer 2.
For cross-communication between the VLANs, you need a router to route at the layer 3
level. The VLANs can be thought of as layer 2 broadcast domains.
The IEEE 802.1Q Ethernet frame is shown in figure 1. The VLAN ID specifies to which
VLAN the Ethernet traffic belongs. This feature can be used to define a fixed voice VLAN,
so that all VoIP telephones can be kept on a dedicated VLAN, with a higher layer
switching at routers or switches.
Figure 1: IEEE 802.1Q Ethernet tag
VLAN tagging is useful when VoIP telephones are used on internal networks. The QoS
feature can be used to prevent timing-critical services, such as voice, from being
interrupted by other less timing-sensitive services, such as data transmission.
As a security feature, the SMG allows the connection of different VLANs to different
physical interfaces on the SMG, with only the inter-VLAN traffic being passed to the
CPU/router. The allowed VLAN tags are configured on the router and any tagged traffic
that does not belong to the allowed VLAN tags group will not be allowed.
2.1 Configuring the router for VLAN
The Virtual Access router has a 4 port Ethernet switch. This switch can be grouped as a
complete segment or as individual segments.

2: Introduction to VLAN
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To configure a global setting, from the Start page, click Advanced -> Expert view ->
system -> Ethernet -> system. The System page appears.
Figure 2: The Ethernet system page
Field name
Description
Command Line
VLAN Enabled
Configures Ethernet switch for
VLAN tagging.
Option
Description
yes
Enables VLAN
no
Disables VLAN
Set Ethernet vlan tags
enabled
Media Sense Enabled
Media Sense shows whether or
not changes in the Ethernet
physical state are reflected in
the routing table. If disabled,
the ports will always stay up at
the IP level regardless of
whether the physical cable is
plugged or unplugged.
Set Ethernet media
sense enabled
Table 1: The Ethernet system fields and their descriptions
Note: when you have enabled the Ethernet switch for VLAN tagging, the Ethernet switch
is no longer a segmented LAN and it defaults to a logical interface based on the assigned
VLAN tags.
2.2 Configuring an individual interface for VLAN
To configure an interface setting, from the Start page, click Advanced -> Expert View
-> interface -> eth-x -> vlan interface. The Ethernet Interface page appears.

2: Introduction to VLAN
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Figure 3: The Ethernet interface VLAN page
Field name
Description
Command Line
VLAN Tag
Defines the VLAN tag ID for a
logical interface.
Option
Description
Minimum
value
0
Default
value
0
Maximum
value
65535
Units
Unspecified
Set the Ethernet interface
VLAN tag to eth-x, y where x is
the interface and y is the VLAN
tag.
Set Ethernet interface
vlan tag
Table 2: The VLAN tag field, description and command line
2.3 Viewing VLAN tags
When you have enabled VLAN tagging, to view your tags, from the Expert View Menu,
click operations -> performances -> interface stats -> VLAN table. The VLAN Info
page appears.

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Figure 4: The VLAN information page showing Ethernet VLAN mapping
Alternatively, you can use a Telnet session to issue the following command:
Show Ethernet vmap
VLAN Tag Logical If
-------- ----------
0 Eth-0
100 Eth-1
200 Eth-2
300 Eth-3
Port Neg S100 Fulldpx Loopbk Pwrdown Isolate Quality Loop?
---- --- ---- ------- ------ ------- ------- ------- -----
A 1 0 0 0 0 0 0 No
B 1 0 0 0 0 0 0 No
C 1 0 0 0 0 0 0 No
D 1 0 0 0 0 0 0 No
Table 3: Screen grab showing results of the show Ethernet vmap command
2.4 Deployment scenario example
The use of VLANs in a VoIP scenario is very important. You can use VLANs to optimise
QoS control and to reduce the number of Ethernet cables used.
You can tag Voice traffic from the LAN to allow the router to apply the appropriate QoS
settings.
When PCs and IP phones exist on separate VLANs, you can use a single Ethernet cable to
daisy chain the PC from the back of the IP phone to reduce cable runs or the number of
Ethernet ports used.

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Figure 5: An example of a deployment scenario
Command Line
Set Ethernet interface vlan tag = eth-0,0
Set Ethernet interface vlan tag =eth-1,100
Set Ethernet VLAN tags enabled = yes
Table 4: Command lines used for the deployment scenario
2.5 Debugging VLAN
To view the Ethernet switch information, in the Expert View menu, click operations ->
performance -> interface stats -> ethernet switch. The Statistics for Ethernet
Switch page appears.

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Figure 6: The statistics for Ethernet switch page
Alternatively, you can use a Telnet session to issue the following commands:
Show switch info
Show switch table

3: CDP
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3CDP
The CDP feature on the router allows it to pass out CDP MAC address broadcasts. This
broadcast can indicate to a client host what VLAN tag to use. Certain IP handsets are
enabled as CDP clients by default.
This means that IP phones that are required to operate on a specific VLAN do not have to
be pre-staged. In conjunction with Virtual Access’ phone provisioning service, IP phones
and routers can be shipped directly to a customer site requiring no pre-configuration.
3.1 Configuring the router for CDP
To configure the router for CDP, from the Start page, click Advanced -> Expert View -
> system ->Ethernet -> CDP server. The CDP Server page appears.
Figure 7: The CDP server page
Field name
Description
Command Line
Enabled
Enables or disables CDP (Cisco
Discovery Protocol) for
advertising Voice VLAN ID.
Option
Description
yes
Enables CDP
no
Disables CDP
Set CDP server enabled
=yes
Voice VLAN Id
Defines Voice VLAN Identifier
to be advertised.
Option
Description
Minimum
value
1
Default
value
1
Maximum
value
65535
Units
Unspecified
Set CDP server voice
vlan identifier = 100
Time to Live
Defines Time to Live for CDP
Set cdp server time to

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broadcast.
Option
Description
Minimum
value
0
Default
value
180
Maximum
value
65535
Units
Secs
live =180
Broadcast Interval
Defines broadcast interval in
seconds.
Option
Description
Minimum
value
1
Default
value
60
Maximum
value
65535
Units
Secs
Set cdp Server
Broadcast Interval
Table 5: The CDP server fields, descriptions and their command lines
The critical setting is number Voice VLAN Id. This specifies the VLAN tag to offer as part
of the CDP broadcast. Any host acting as a CDP client will use this tag.
3.2 CDP flows
The table below describers the flow and mapping between CDP and DHCP.
Figure 8: Flow and mapping between CDP and DHCP
3.3 Debugging CDP
3.3.1 Tracing using the command line
Tracing via the command line is more flexible than using the trace analyser as you can
specify the event severity and use the all class event to trace all event classes.

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Command line tracing also allows you to trace to a log file for examining events over a
protracted period of time.
If you enter no event severity, all event severities are displayed.
If you choose an event severity, all events of the chosen severity and greater are
displayed.
To stop tracing, entering –(minus) followed by the event class will stop tracing for this
event class. Entering –(minus) on its own will stop all tracing.
Syntax
Description
++cdp
Starts tracing CDP events
-cdp
Stops CDP tracing
Table 6: The command line tracing syntax and their descriptions
Show cdp server info
CDP Server info
Enabled: yes
Voice VLAN id: 100
Broadcast interval: 60
Time to live: 180
Table 7: Output from the CLI command show cdp server info