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VLANS FOR VOICE

Hello ,

            I am making a project of some hotel. And there will be near about 750 ip phones and 1000 analog phone that is going to connect with VG224.

          I have all my links 1 giga bit port and Uplinks are fibers. I have created one vlan for my whole voice network and other vlan for data. And my question is that how many ip phones should be there in a single VLAN so that we can avoid broadcast ARP packets. And if there should be another vlan for voice than how can i make that. And what will be the benifits of that.

pankaj sharma
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Blue

VLANS FOR VOICE

Hi,

I dont believe we have any kind of best practice for maximum number of ip phone per vlan case.

But I think if you want you can create number of different voice vlans and divide phones in different vlans. Keep only one voice vlan per switch. So connecting 750 phone, you  will have multiple switches and you can creat multiple voice vlans.

Regards

Ronak Patel

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Regards Ronak Patel Rate all helpful post by clicking stars below the answer.
Hall of Fame Super Silver

VLANS FOR VOICE

From CUCM SRND:

Layer 2 Access Design Recommendations

Proper access layer design starts with assigning a single IP subnet per virtual LAN (VLAN). Typically,

a VLAN should not span multiple wiring closet switches; that is, a VLAN should have presence in one

and only one access layer switch (see Figure 3-2). This practice eliminates topological loops at Layer 2,

thus avoiding temporary flow interruptions due to Spanning Tree convergence. However, with the

introduction of standards-based IEEE 802.1w Rapid Spanning Tree Protocol (RSTP) and 802.1s

Multiple Instance Spanning Tree Protocol (MISTP), Spanning Tree can converge at much higher rates.

More importantly, confining a VLAN to a single access layer switch also serves to limit the size of the

broadcast domain. There is the potential for large numbers of devices within a single VLAN or broadcast

domain to generate large amounts of broadcast traffic periodically, which can be problematic. A good

rule of thumb is to limit the number of devices per VLAN to about 512, which is equivalent to two Class

C subnets (that is, a 23-bit subnet masked Class C address).

The recommendation to limit the number of devices in a single Unified Communications VLAN to

approximately 512 is not solely due to the need to control the amount of VLAN broadcast traffic. For

Linux-based Unified CM server platforms, the ARP cache has a hard limit of 1024 devices. Installing

Unified CM in a VLAN with an IP subnet containing more than 1024 devices can cause the Unified CM

server ARP cache to fill up quickly, which can seriously affect communications between the Unified CM

server and other Unified Communications endpoints. Even though the ARP cache size on

Windows-based Unified CM server platforms expands dynamically, Cisco strongly recommends a limit

of 512 devices in any VLAN regardless of the operating system used by the Unified CM server platform.

HTH,

Chris

Community Member

VLANS FOR VOICE

But will it not effect to make different subnet for the same voice network

pankaj sharma
Hall of Fame Super Silver

Re: VLANS FOR VOICE

Of course not, good network design always results in many Vlans.

Sent from Cisco Technical Support iPhone App

Community Member

VLANS FOR VOICE

That means If the CUCM that is the tftp server of all the ip phone will have different subnet does not create any problem. And one Question also I would like to ask for how many ip phone i can make my call manager as a DHCP server. It is basically an IBM server that can handel up to 3500 ip phones.

pankaj sharma
Blue

VLANS FOR VOICE

Hi,

Yes it will not create any problem. You have to make sure that you have routing done between the VLANs.

We only support one DHCP server per cluster, so I think one DHCP server can handle full cluster load.

Regards

Ronak Patel

Rate helpful posts.

Regards Ronak Patel Rate all helpful post by clicking stars below the answer.
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