VoIP phone wont configure

pereigroup used Ask the Experts™
I have some new VoIP phones and for some reason they will not configure on my clients network, when i took them home they work perfectly. I tried Wiresharking on a hub to capture the traffic, however i am at a loss as to what it means of what is causing the issue. The DNS is our Win2012R2 server and this then forwards on to the public Google servers.
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this capture show you
first: try to establish a FTP connection (TCP21) to
second: send a TCP-RESET immediately as answer back to

what can be seen from this?
- routing is OK, because the hosts communicate
- don't accept the connection ... possible the pones come from an not allowed subnet or located within the false VLAN, or the local Firewall or FTP Serice is configured incorrectly


Thanks Dirk for the response.

The subnet on the DNS is so allows IP ranges to, the phone IP is and the server IP is so both are within range of the same subnet

We dont use VLAN on our network

I temporarily disabled the firewall on this server during the testing because it was blocking the communication (i will fix this later), so the firewall is not the issue.

The FTP service is not on our lan, it should be forwarded externally to the phone provider.
can't recognize any forwarding.
there is traffic between microsoft (hyper-V i think) and polycom only.
and the (virtual) device with microsoft-MAC address send the session-reset.

if this is a virtual router/firewall/VPN/gateway, you should check the logfiles here.
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This is a virtualised server running DNS and DHCP, the gateway/firewall/WAN is a physical device which is, i would need to run Wireshark on the server to see if any traffic was being forwarded to on from the DNS to elsewhere.

It seems that from what you are saying that the Polycom phone is trying to establish a FTP connection with the DNS server which it has no facility to facilitate. I dont know where to go from here. I spoke to the providor and they said the phone should be communicating on port 5060 which there is no traffic on.
Port 5060 is SIP. The Phone use this Ports to establish calls. The phone must be connected to the call-server and ready booted before.
I think the phone try to get the Firmware/Configuration via FTP while booting.
Possible you have to configure the phone-server as DHCP-option.
Check: https://community.polycom.com/t5/VoIP-SIP-Phones/FAQ-How-can-I-setup-my-Phone-Provisioning-Download-Upgrade/td-p/4203


Thanks for the reply, it is a cloud based phone system, so i dont have access to the phone-server, when plugged the phones in at home it just worked (granted different IP range).
Distinguished Expert 2018

Could you please show the settings for your DHCP server? More specifically, what options your DHCP server is sending. Sounds as if your phones are receiving a DHCP option that is causing them to try looking at the wrong place for FTP connections.

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