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How to connect UC520 behind Cisco router 876W



What will be the best way to connect the UC520 behind a Cisco router 876W for ADSL.

In holland we have to use a ADSL router first and then the UC520.

At this moment the SIPcommunication from the outside world will not reach the UC520.

Any help is welcome.


Eric Oosterbaan

SMB Engineer - The Netherlands.

See also:

6 Replies 6

cindy toy
Rising star
Rising star

Hi Eric,

Please post your question to this link:



Regards, Cindy If my response answered your question, please mark the response as answered. Thank you!

Steven DiStefano
VIP Alumni
VIP Alumni

You set up FE0/0 WAN interface of UC500 to connect to the DSL  modem or the T1 IAD/ISR to connect to the Network of the SIP SP.  In these cases, this DSL or T1 router will be the demarcation router of the SP network interconnect.

The configuration for the SIP Proxy, Registrar, Authentication credentials, DID mapping, etc is all done on the UC500.

The Internet Router is managed by the service provider & provides network access services for IP voice and data traffic. It is essentially the DGW and next hop router for the UC520.  The UC520 still must have a routable IP address. The Managed Access router needs to provide the following to make it a viable solution for the SIP Trunk Enabled UC520 IP-PBX.

-         NAT & ALG functionality

-         QoS for SIP Trunk calls & SLA guarantees

-         WAN conversion to Ethernet on UC500

-         Well defined point of troubleshooting for SP & customer

The SR520 offers increased Firewall, beyond what is in the IOS of the UC520, so it makes a compelling case for use.  It also supports all of the above.


To complement Steve's answer, please refer to the following document that covers some design considerations:



Dear All Posters,

The reason that I bring in the question 'How to connect UC520 behind Cisco router 876W' is that we have a lot of (white)papers to read and to give many ideas how to handle a router configuration, UC500 series configuration .. etc.

But what we need, is a 'short track' .. ' in this way you have to configure your minimum router requirements and minimum requirements in the UC520'.

What I need NOT ...

This will be a document that you can help you further ..

This is the basis rules how to open your 5060 ports

This is the best rule for the 'dialer patterns'


We need a good handout ...

I have an ADSL line -

I have a perfect Cisco router ( 876W or SR520 )

I have a perfect UC520 box

And this YOU have to bring in, in both systems to make them doing te right job for you.

Answer the phones,

Give the user the right connections he or she wants...

And monitor the costs of the connections.

All the config (E-)papers I have read, will give a very usefull explanation of the configuration of the UC520.

But nothing you can find .. about the minimum configuration area of the ADSL routers in front of the UC520.

I hear you thinking .. why .. are you not an Engineer .. are you not expert with Cisco engineering ?

No .. I'am an Senior Engineer who wants to make a good custom solution ... and if the solution will have some trouble .. to fix it ..

So we have to study on it ...

The documents that you give in this reply, I found a few days before I started this discussion .. it give you a wide idea how to fix or to start with a configuration ..

That is basic information .. now we need a working solution .. THAT kind of information we are (sorry I am ) interested in it ..

Ok .. some english is my strongest point .. but I think you understand what I mean ..

Hopefully, I have give you the push .. to make my question .. and I'am sure more engineers will ask the same ...

Many regards,

Eric Oosterbaan

SysCoData - The Netherlands


Point taken. I hear you loud and clear. Unfortunately, we do not have something specific for all possible configuration permutations. That said, let me try to dig out some more documentation that can be useful in your deployment. I will get back to you ASAP.




Here is one document that describes, step by step, how to provision an SR520 in fron of the UC500. Is this what you are looking for?



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