Callmanager, Cisco VOIP and Subnetting

[Bimson]

Hello,

at the moment we´re restructuring our network. Currently we´re using more than 300 Cisco Vo-IP-Telephones in two /24 subnets. To make our network easier, we would like to transfer the two /24 subnets into a /23 subnet.

We´re using the Cisco Unified CM Ver.: 10.5.1.11901-1 in combination with Cisco 7851 telephones.

Are there any known problems using an subnet bigger than /24 in combination with the Cisco CM and the Cisco VoIP telephones?

Greetings from Germany,

Bimson

[Jaime Valencia · Accepted solution]

From the SRND

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. 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.