1120E, 1140E Subnet Size

[telecomteen]

Hi,

I have about 500 1120E and 1140E IP sets connected to a CS1000E. The network topology is flat, all phones share the same subnet with over a thousand computers and other network clients. Recently, the phones are not registering correctly with the node when they are rebooted or newly provisioned.

When sniffing the traffic, the phones generate ARPs, get replies, but then ARP again. They also exhibit similar behavior of sending TFTP requests, getting replies, but then sending more TFTP requests.

When connected to a smaller VLAN with fewer devices, the phones register correctly.

**Is there a particular limit (MAC address table size, ARP cache size) of devices that the 1120E and 1140Es can co-exist with?**

 

[biv343]

Not necessarily, but you're going to have a heck of a time with QOS and network performance in general with that many devices on a single VLAN.

I'd recommend configuring a seperate voice VLAN, then configure the voice VLAN in the phone to tag the voice packets to the voice VLAN. The PC port in the phone would pass any connected device to the data VLAN, while the voice packets would be tagged and connected to the voice VLAN. It would take a small bit of configuration work on the data gear/DHCP server to make that work, but you'd be much happier with the performance of the phones.

I've heard recommendations that in an ideal world there wouldn't be any more than a couple hundred phones on a single VLAN. I've run 400+ phones on a single VLAN without issue. Either way, I'd recommend getting the phones on their own VLAN separate from the PCs and what not.

 

[tnphoneman]

What we have done with that many phones is

1 vlan /24 subnet for TLAN PBX equipment
1 vlan /24 subnet per floor/building for phones
1 vlan /24 subnet per floor/building for PCs

Keep them all separate and you can also give the vlan for the tlan and sets priority.


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