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New Member

Silent Monitor on Cat3550 possible?

Hi All,

I am setting up a Cat 3550 SMI for silent monitoring. It looks like I have to be able to span both rx and tx (agent phones) to the destination port (IPCC server).

The problem is I have 7 agent phones and the 3550 will only span rx & tx on ONE source port per span session, unlike the Cat3524pwr.

I have thought about spanning the port from the gateway (single T1 pri), but that means spanning ALL voice traffic, not just the Call Center. Note, all voice traffic is on a single vlan, this is a small system.

Are there any workarounds here?

Thanks, Randy


Re: Silent Monitor on Cat3550 possible?

On a 3550 the SPAN port does not support bi-directional communication. You need to setup the second port on the CRS server. Then, make sure you have the voice gateway and the CRS server second NIC plugged into the same switch. Lastly, just SPAN the port the voice gateway is plugged into. That way, if all your agents are in the same VLAN you can monitor Agent to PSTN calls. Post more questions if you have any, I have to run out and can post more specific instructions later. Hope this gets you started. Link below walks you through setting up second NIC on an already built system.

/andy - berbee

New Member

Re: Silent Monitor on Cat3550 possible?

Thanks, that makes sense. Yes, we have set up the second NIC on the server. The system went live yesterday and I will wait for things to settle down before implementing Silent Monitor.

Theory question: Once I SPAN the gateway to the Server, how does Silent Monitor recognize each call flow? By destination IP (the phone), or is the DN hidden in the UDP packets? I'm assuming it filters out all traffic except RTP packets.

Thx, Randy


Re: Silent Monitor on Cat3550 possible?

If uses the MAC address of the agents phone and you are correct in saying that it just forwards the voice RTP packets to the Supervisors PC.

New Member

Re: Silent Monitor on Cat3550 possible?

Is it necessary to install a seoncd NIC on the CRS server. The document that describes how to set up silent monitoring and recording say that a second NIC is necessary when access switches that have agent phone attached are trunked back to a distribution switch. Basically my scenario is a small installation where I have a 3550 switch, 8 agent phones and an IPCC server running 3.1.2. I've read other posts (along with some content mentioned in this one) that I can just enable a SPAN source port on the Gateway and a SPAN destination port where my IPCC server is plugged into. Is that correct? If so, this is the config I am looking at.. Please verify if it is correct. Thanks a lot for any help.

Fastethernet 0/1 will be the gateway and 0/10 will be the server.

Switch(config)# monitor session 1 source interface fastEthernet0/1

Switch(config)# monitor session 1 destination interface fastEthernet0/10 encapsulation dot1q

Switch(config)# end

Switch# copy run start


Re: Silent Monitor on Cat3550 possible?

That is correct the 3550's do not support bi-directional communication on a SPAN port so you will need to enable the second NIC on your CRS server as explained in this DOC:

Config looks correct as long as your voice gateway is in fe 0/1 and your second NIC on the CRS server is in fe 0/10

New Member

Re: Silent Monitor on Cat3550 possible?

Thank you for your quick reply. What if I used a 3524 switch? Would I still run into the same issue?

Using 1 NIC on the CRS/IPCC server plugged into fastethernet 0/10 and agent phones plugged into ports 3-6 and the below config:

Switch(config)#interface FastEthernet0/10

Switch(config)#port monitor FastEthernet0/3

Switch(config)#port monitor FastEthernet0/4

Switch(config)#port monitor FastEthernet0/5

Switch(config)#port monitor FastEthernet0/6


Switch#copy run start

Thanks again for any help you can give.


Re: Silent Monitor on Cat3550 possible?

You would not have the same issue on a 3524, one NIC will work. As for your config, that will work. However, don't you want to monitor Agent > PSTN calls or just Agent to Agent calls. If you want to monitor PSTN > Agent calls you will also need to span the port the Voice Gateway is plugged into.


New Member

Re: Silent Monitor on Cat3550 possible?

Thank you again for your reply. It seems like the SPAN feature is a little nicer on the 3524 and this network has both a 3524 and a 3550 connected together using the gigastack GBICs. I used the configuration I sent in my last post and included the gateway port as well. I tested it yesterday and it seems to be working well. Thanks a lot for your help.

Take care,


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