Comment: Router-On-A-Stick Article

Hey All, I would first thanks the guys behind Cisco Knowledgebase Articles, they are extremely helpful in topics, depth and illustrations.

And I would appreciate if you accept my comment on the article “Router-On-A-Stick”.

I did use this technique with a Cisco Call Manager Express 2821 Router Model and a Cisco Switch 3750G.

Hopefully my comments will be reviewed first and if they are right they will help to tweak the Article in the right direction.

1. I have noticed that the Article did not mention a very important point and that is the Interface on the Router to be configured as a trunk port has to be at least a Fast Ethernet Interface, so an Ethernet Interface on a Router will not do the job.

You will be able to create the subinterfaces on the Ethernet Interface but once you try the encapsulation command to implement a dot1Q or ISL encapsulation type the IOS will throw you an unrecognized Message.

2. VLANs creation on the Switch is not the right way. When you type interface VLAN1, that is the Switch Interface Management, we put IP address on the switch Interface Management which is VLAN 1 to be able to Telnet to the switch for remote management or use Cisco Tools for remote configuration, so it does not relate in any means to VLANs creation.

[code:1]SW1# configure terminal
SW1(config)# interface vlan1
SW1(config-if)# ip address 192.168.0.2 255.255.255.0
SW1(config-if)# exit
[/code:1]
In the above lines the Interface Management VLAN 1 assigned an IP address to be able to Ping or Access the Switch Remotely regardless if there is VLANs created on the switch or not. This Interface is only for Management Purposes

3. The write way to create a VLAN on a switch is simply the command: vlan <number>

[code:1]SW1(config)#vlan 10
SW1(config-vlan)#name VOICE
SW1(config-vlan)#exit
SW1(config)#
[/code:1]
By the above technique I created a VLAN 10 and named it VOICE to refer that this VLAN 10 is for VOICE

[code:1]SW1(config)#vlan 50
SW1(config-vlan)#name DATA
SW1(config-vlan)#exit
SW1(config)#
[/code:1]
By the above technique I created a VLAN 50 and named it DATA to refer that this my DATA VLAN

4. After creating my VLANs for DATA and VOICE, I then start to assign the desired ports to my VLANs

[code:1]SW1(config)#interface fastEthernet 0/3
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 50
SW1(config-if)#switchport voice vlan 10
SW1(config-if)#exit
SW1(config)#
[/code:1]
By the above technique I have placed the Fast Ethernet 0/3 Port on the Switch into two VLANs.

The DATA vlan 50 referred by the access parameter, and the Voice vlan 10 by the voice paramter.

Please not we always give the VOICE VLAN a lower number than the DATA VLAN because lower VLAN numbers have precedence and high priority if a failure happens in our infrastructure.

For example if we have multiple switches and a switch or a path went down the lower VLAN traffic will take precedence over the higher VLAN numbers, in that case we want or VOICE traffic to be prioritize over other traffic like DATA.

5. We never put the command spanning-tree portfast on a trunk port, this command is only used when and interface is in access mode and is directly connected to an End Device like IP Phone or Host or Server. Applying spanning-tree portfast on a trunk port leads to loop occurrence in our network.

6. Router-On-A-Switch can be used not only when we have Call Manager with VOICE and DATA traffic. It is used if we have multiple subnets in our network and we need to allow communication between these VLANs, Inter-VLAN. In this case we can also benefit and apply Router-On-A-Stick Technique.

Hopefully my points will be beneficial, Thanks for listening.

2/3. Your way of creating VLANs is indeed how things went before 12.1(T) i believe. Currently creating an SVI and assigning your access ports will do the trick. This indeed does not give your VLAN a name. For your administration it is most recommended to give your VLAN a name.

4. the number of your VLAN will not determine if your VOICE or DATA has privileges. To make data/voice more important you have to classify and use QoS to give a guarantee that Voice will be more important than Data.

5. Good point. Making the trunk port a portfast is only desirable when having a single uplink or on the access ports.

hey Chojin, thanks for your reply.

I did not worked with SVI for now, I only know that SVI represents a logical layer 3 interface on a switch. but thanks for the information.

Sorry I did not mean it in a privilege way, but I only recall from my study that giving your VOICE lower VLAN number than your DATA VLAN will help takign precedence in case of redundancy failure, so the lower VLAN number will be processed before highe VLAN numbers. Although, I should maybe check my info again.

I hope the fellows responsible for the Article will check our info first, test them, and if right modify the Article for better results.

thanks in return,