UC320 Packet Flood

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Apr 3rd, 2012
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I have just setup a UC320 for a client and it was working without trouble for the last few days up until last night. It is now taking out my entire network and causing a packet flood. When i disconnect the device from the network all comes back up ok and i can then reconnect the UC320 and all goes back to normal for a while until it happens again. I cant seem to see any pattern to it though.

I have a few things that i can think of that might be causing it. First of all, the WAN port IP is on the same subnet as the LAN IP. This is because the router i am using doesnt support a seperate WAN subnet. (Topology is Route Voice Only) I am only using the device for voice so i could always put these on seperate subnets but my thinking up until now has been that i need to be able to access the config remotely from a machines within that subnet.

Both the WAN and the LAN ports on the device is connected to an SG300-10P and all handsets are powered via POE. The SG300 is also connected back into the main network. I would have thouht that if there was an issue with the UC320 flooding the SG300 would shut that port down using Spanning Tree.

I also figured that the WAN and LAN port must be routed seperately within the device therfor not causign a loop. If this wasnt the case then i would have a constant loop but the device has and does work in the configuration just not all the time.

As you can tell by now im pretty new at this and this is my first of hopefully many installs.

Any advice would be greatly appreciated as i am struggling to get on top of this one.


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nalbert Tue, 04/03/2012 - 10:56
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The UC320 is not only a PBX, but it is also a router. So the WAN and the LAN ports have to be on different Subnets. The correct design for your case is defined in the Smart Design Document " Deploying UC320 in an Existing Network". If you do not have a router that meets the criteria, I would recommend eliminating the router and using the UC320 as the router.

Documentation: https://supportforums.cisco.com/docs/DOC-14783

If that is not possible then the only other option you have is to unplug the WAN interface on the UC320. This is going to cause following side effects

* No voicemail to email

* Time has to be set manually ( since NTP goes through WAN) or a local NTP server needs to be created.

* No Cloud Services ( Auto upgrade, upload WAV file)

Christopher Edg... Tue, 04/03/2012 - 14:00
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The other option is to plug in the UC320W inline with the other router so you have:  Internet -- edge router -- UC320w -- Phones + PCs


Dturner4777 Wed, 04/04/2012 - 03:22
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so would the uc320 need to be setup to route voice and data then, and we would bridge the internet modem, or would the pc's pick up dhcp from the adsl router if they were plugged into the uc320w

Christopher Edg... Wed, 04/04/2012 - 07:15
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Hi David,

In this scenario the PC's would pull DHCP addresses from the UC320 (192.168.10.x by default).  The UC320W WAN interface would pull a DHCP address (by default) from the internet modem.  You can configure port forwards on the UC320W if there are services you need to be able to access from the internet on your PCs.


rstfelix1 Sun, 05/05/2013 - 11:53
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Hello Chris and Navin,

It would be nice to have access to the document "Deploying UC320 in an Existing Network". Only Cisco partners seem to be able to access it.

Anyway, I may have the same issue. The configuration I'd like to achieve is as follow:

Internet --> Cisco RV220W --> Switch --> UC320W and all other devices connected to that switch.

If I understand correctly, it is necessary to configure the UC320W WAN interface on a different subnet.

To do that, I would create a new VLAN on the RV220W and assign a port to it. Then, connect the UC320W WAN interface to that port.

Is there anything else I would have to do to prevent network issues like “packet floods” and others?




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