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UC520 on own LAN behind existing router


I currently have a SPA9000/SPA400 on a vlan/subnet behind an existing non-cisco firewall / router. I am looking for more functionality and reliability and have acquired a UC520 which I plan to swap for the SPA combo.

I have seen a document for putting a UC520 behind a CISCO router but the UC520 still uses a WAN port and WAN IP to connect to the router.

I want to achieve the following because I don't want to touch the existing non cisco router config.

  • Want UC520 on LAN just like SPA9000/SPA400
  • Only want a single network on the UC520 10.0.10.x
  • Do not need any firewall or NAT on UC520
  • Do not need any VPN functionality on UC520

  • Existing router is and is DHCP / DNS server and supports DHCP option 66/TFTP
  • Want UC520 to be
  • Handsets currently allocated DHCP via mac address so that IP matches extension 10.0.10.ext
  • Have 1 SIP trunk and one FXO

I am well versed on the SPA 9000 but totally clueles about the UC520. Essentially I am looking to straight swap the UC520 for the existing SPA900/SPA400 without reconfiguring my VoIP LAN.

Is the above easily done?



paolo bevilacqua
Hall of Fame Master

Yes, it can be done easily, however you would hookup the UC500 via EXP port, not WAN.

Thanks for replya Paolo, can it be done using CCA only or is CLI required?

Do you know if there is a step by step document available somewhere?

I think it can be done with either methods. Not sure about 'step by step guide', as in general it is better to have an understanding of things before, or hire a certified/knowledgeable engineer.

Also note that if your WAN router is non-cisco you will likely having much trouble getting the SIP trunk to work.

David Trad
Rising star

Hi GT,

Firstly I should caution you about running a flat network when voice is involved, considering that you are installing a UC-520 to replace the SPA9000, you will have the ability to have the UC work VLAN's and also do Inter-VLAN-routing which is a valuable resource to have, it also will not effect the network topology.

Whilst CCA can support the configuration of a flat network (Not easily I must add) it is not a recommended SmartDesign as per Cisco's deployment guidelines, and their reasoning is valid for this.

What you want to achieve can be easily done especially with the assistance of CCA which has a Wizard that will guide you through the process, this Wizard is one of the best I have seen In the industry and whilst it can do with some minor improvements, it does allow for a non voice engineer to get a basic system built, but in saying that the Wizard does not cover any advanced setups such as that of a flat network.

Please listen to Paolo's recommendation of engaging a voice engineer or at least a Cisco certified voice engineer, he is right in saying that one should have a sound understanding of Voice networks (topology) before working on them, small mistakes can turn into disasters which one should avoid.


David Trad.

Cheers, David Trad. **When you rate a persons post, you are indicating a thank you or that it helped, but at the same time you are also helping to maintain the community spirit - You don't have to rate posts and you wont be looked down upon :) *


Thanks all for suggestions and help.

Whilst i agree a flat network for the UC500 is not the best way to go I am bound by existing infrastructure and VPNs etc.

From playing with the UC500 offline and reading up more I realise I should leave it as the DNS and DHCP for our voice VLAN and just use the existing router as the gateway and nothing else.

So my requirements are simpler now I just want to set it up without a WAN connection and with internet accessible just via the gateway.


Ok I am at the stage where I just need to change the gateway address of VLAN100.

I have the VLAN100 IP address of the UC520 set to / and I want to set the gateway to but try as I might CCA insists on keeping the gateway at and this is preventing my SIP trunks from finding the router out.

Can somebody please tell me how to change the VLAN100 gateway address?



Can't you change the SIP trunk then?

Anyway, in Cisco IOS:

interface x/y

ip address

Again, unless your router has sip support you may encounter trouble, one way voice, etc.

Apologies for my complete IOS ignorance.

Could you give me the full syntax for changing the gateway address (default router) of VLAN100 please.

I take it i get to IOS by telnetting to the ipaddress of the UC520 on VLAN100?

Again apologies for my IOS ingnorance

There is nothing to apologize for not knowing someting, the point is that you're trying to do a job without having the necessary minimal skills. That will likely cause poor results, much frustration for both of you and your customer.

Notem Already Cisco SM doen't support CLI changes to UC500, so really it seems to me you are not taking the right road there.

Again, you can conveniently hire someone with knowledge, and he/she will sort everything out for you.

The alternative is that you start learning IOS as everybody else that uses Cisco does.

Hello Paulo,

Just to clarify I'm setting this UC520 up for myself not for a customer so only i have to suffer the concequences of a misconfig.

I simply need to change the VLAN100 gateway/router IP.  I've no need to invest in learning IOS or hiring an expert I just neet to change a single IP.

I am certified in another router brand but just have a need to change a SPA9000/SPA400 combo for something more reliable and once it is setup I wont' have a need to go near it again.



Hello Gavin,

Just make the default route of the UC to point to the

ip route

and remove the other default route if any. This way the default route for the UC will be



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