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Cisco UC540 share LAN with another Router

Level 1
Level 1

Hi Guys,

Quick question....

Can a UC540 be used as generic device and not as a gateway on a LAN ?

I ask because we already have site to site hardware VPN with cisco RV series routers between 6 buildings and we dont wan to change it.

My idea was to have the following setup :

SITE A:      LAN     Router RC220 ---> Connetced to WAN      LAN    UC540 with nothing connected on WAN port and static route to

Is this a viable option/cheat ?

Like i said we do not want to change the RV routers/config for site to site and the fact that they are the default gateway....   and in this case i only have 1 public IP to perform the setup.


5 Replies 5

Level 1
Level 1


My initial question is what are the business/operational goals of the UC540? Your suggestion can work. The wan port on the UC540 is an outside interface so it can't be used in the configuration you're designing. The UC540 layer-2 uplink port would need to connect to the uplink L-2 port on the router, making sure both are on the same subnet, verify speed, duplex,trunking requirements. Then set the default gateway on all devices to the the RC220.

Just keep in mind that the advance features on the UC540 outside interace are no longer usable. Other concerns are outbound/inbound IP telephony calls. No problems with the FXS/FXO calls, however wan T1 services may not be available? Are you using SIP, cable, or dsl?

Lastly, before undertaking this design, check to see if is defined in Cisco design guides. At first glance it seems unorthodox. Weigh the business/operation goals to your design options.


Lol... yeah it does feel unorthodox .

The reason is that we already have all the "networking/site to site vpn" setup between all our buildings 6 of them (all cable with 1 static IP).

Now one of the managers decided to buy a IP phone system to test it. It's a UC540 with 4 lines FXS/FXO.

We already have it setup the way i mentionned above... i didnt want to make it my primary gateway yet as we want to test it. 

First my reseller wanted to plug the WAN port of the UC540 to my actual LAN but that felt even more unorthodox.....

Any way the unit is up, at IP and has a static route of to

Seems to work....  but for some reason i cant get it to do email notification for voicemail.    config seems legit, can ping to the internet OK.  Option are enable... 24hours.... email is valid....  Even tried notification to my CELL and it doesnt work either....

The only thing is that i'm trying to use my ISP's SMTP server.... could this be the issue ??

and for the "advanced features on the UC540 outside interace" can i just use port forwarding on my WAN router to  or is there a technical limitation on the UC540 tha prevents that?

lol... so many questions... if the UC540 proves easy enough/reliable/versatile it might one day replace the RV220 that we currently use.

Thx for your time and sorry for the typos... tired like Hell

one last question :  My reseller told me not to do config on this device (UC540) via CLI as it might void the support we can get from cisco... ever heard about this ???   

I love CLI and used to work only with that on my old ASA/3500 Catalysts/1800 etc........


Hello Carlos,

You should make static route (if the 220 cannot ping CUE at the 220 to the CUE network with gateway the UC Vlan1 if this is your data vlan on your UC. You should check if you can ping from (if this is your CUE - voicemail ip address) to and vice versa. Also you if you can ping from some server in Internet. The easiest setup is if your SMTP is using port 25.

If you prefer you may open a case with SBSC and resolve the issue.

Best regards,


*Please rate helpful posts

You guys rock!!!!

Thx for all the infos... will try the route later today.

Is there a way to force the system to resend the notifications ?


Carlos, as you know the UC540 can support a variety of configuration. Since you are testing this unit, you can experiment with different options. As the reseller stated, yes you can connect the UC540 into a LAN port. Just need to assign the outside interface F0/0 an external static IP that's on the d/g subnet. There should not be any acl conflicts since the subnet is already defined for the d/g on the firewall. The SA500 supports this type of configuration also.