configure vlans for my video network

[Horacio Gutierrez]

Hello,

I have two Cisco video conferencing devices that are located in different locations, I need to know what is the best practice when configuring vlans for this two video network devices to communicate with each other.  Should I just put them on the same vlan or create two vlans one for each Cisco video network device and route does two vlans so the two devices can communicate with each other, keep in mind they will be connected to my 3750 switches and go through my 6509 core switches.  Please le me know what is the best practice.

Thank You.

[Richard Burts]

Horacio

The choice of what is best depends somewhat on the topology of the network and we do not know much about that. How far apart will there video conferencing devices be? Are the 3750 switches acting as layer 3 devices and routing or are they just layer 2 switches and the layer 3 is provided by the 6509 core switches?

In general I think it is a best practice to have each of the video conferencing sites be in its own VLAN and to route between the VLANs.

HTH

Rick

[Horacio Gutierrez]

Hello Rick,

The video conferencing devices are in different cities from San Diego, California all they way to San Jose, California.  the

3750 are acting as layer 2 switches and the 6509 switches are routing between cities.  What is the advantage of having the two devices in different VLANs versus having them on the same VLAN?

Thanks.

[Richard Burts]

Horacio

The big issue is whether any broadcast traffic from one site is forwarded to the other site. Especially if the sites are in different cities I believe that the Best Practice would be to configure separate VLANs.

HTH

Rick

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[Horacio Gutierrez]

Rick,

I thought the reason we put network devices on the same vlan so other the devices on other vlans wont send there broadcasts to that vlan which would make those network devices on that vlan foward traffic faster, but you say the "big issue is whether any broadcast traffic on site is forwaded to the othe site". Can you explain to me into more detail how putting devices on the different vlans espically when those devices will be communicating which each other ofter is better than putting them on the same vlan?

Thanks.

Horacio

[Richard Burts]

Horacio

Perhaps in my attempt to reply quickly I was not clear in my explanation. Certainly the reason that we create VLANs is so that devices in one VLAN will not receive broadcasts from other VLANs. And reducing the spread of broadcasts leaves more bandwidth available for forwarding the traffic that we really care about.

So let us think about the video conferencing devices. If a VC device in San Diego wants to communicate with another VC device in San Diego it will send an ARP request which is a broadcast. Now do you want to forward that broadcast from San Diego over your Wide Area connection to San Jose? And remember that this arp request is not just a one time thing. Devices that are communicating with each other will periodically time our their arp entries and arp again (in some devices they do this every 5 minutes - I have no idea how often your VC devices will refresh their arp entries).

If both San Diego and San Jose are in the same VLAN then all broadcast traffic generated at one site will be forwarded over your WAN to the other site. I think that is not so good and is why I suggest separate VLANs.

HTH

Rick

[Horacio Gutierrez]

So let me gets this right Rick, your saying that if the two devices where in the same location then it would alright to put them in the same vlan because arp broadcasts would not travel across the WAN just the LAN side which really would not slow down the speed as oppose to putting them in the same vlan that would send broadcasts every 5 minutes accross the WAN which would flood that vlan with arp requests and slow down the real live video going accross san jose to san diego. Is that where you saying Rick, please let me know before I go on and design the rest of my video network.

Thanks.

Horacio

[Richard Burts · Accepted solution]

Horacio

Your understanding is very close to what I am trying to explain. All VC devices in San Diego may benefit from being in the same VLAN and VC in San Jose can have a VLAN so that their communication is local.

But if you were to put both VC into a common VLAN then the impact is more than just that VLAN. You have a certain amount of bandwidth available between cities. Do you want to consume part of that bandwidth carrying arp and other broadcast traffic?

HTH

Rick

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