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Subnet mask for more than 1.2k phones

Working in a project of IP telephony which includes more than 1,200 ip phones, and I was wondering what it's the recommended subnet mask to use for the phones, creating several VLANs of course, creating networks with 24 or 25 bits for subnet mask??  Or which subnet mask should I use for this purpose??

Regards,

Juan Carlos Arias

  • IP Telephony
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VIP Super Bronze

Subnet mask for more than 1.2k phones

Cisco strongly recommends a limit of 512 devices  in any VLAN. which is equivalent to two Class C subnets (that is, a 23-bit subnet masked Class C)

There are several reasons for this..

1. The need to control the amount of VLAN broadcast traffic

2. The ARP cache of CUCM (linux based) has a hard limit of 1024 devices, hence 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

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"opportunity is a haughty goddess who waste no time with those who are unprepared"

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"
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VIP Super Bronze

Subnet mask for more than 1.2k phones

Cisco strongly recommends a limit of 512 devices  in any VLAN. which is equivalent to two Class C subnets (that is, a 23-bit subnet masked Class C)

There are several reasons for this..

1. The need to control the amount of VLAN broadcast traffic

2. The ARP cache of CUCM (linux based) has a hard limit of 1024 devices, hence 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

Please rate all useful posts

"opportunity is a haughty goddess who waste no time with those who are unprepared"

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"

Subnet mask for more than 1.2k phones

Hello aokanlawon, thank you for your comments, I'll keep in mind for my design.

One last thing, do you have a link or document where I can find this??  I mean a document from Cisco, just for documentation of project, if you don't have it, no worries.

Regards,

Juan Carlos Arias

VIP Super Bronze

Subnet mask for more than 1.2k phones

Yes, its documented in the SRND here

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/netstruc.html#wp1043617

Please rate all useful posts

"opportunity is a haughty goddess who waste no time with those who are unprepared"

Please rate all useful posts "The essence of christianity is not the enthronement but the obliteration of self --William Barclay"

Subnet mask for more than 1.2k phones

Great, thank you for your time and comments.

Regards,

Juan Carlos Arias

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