Showing results for 
Search instead for 
Did you mean: 

srp521w ethernet sub interfaces on WAN

Level 1
Level 1

Hi there,

Have followed the admin guide, and can setup this up fine, however what we're wanting is to turn off any IP connection for the main wan ethernet interface and only have the sub-interface have an IP connection method.

I can't see how you can turn this off, which is causing a double-up of dhcp requests being sent when using both the main/sub ethernet interfaces to use dhcp.

This has been tested on the 521w and 521w-u versions, and I've just used the latest firmware 1.2.4 on the u version.

How can this be configured so that there is only 1 WAN interface that is using IP (the sub interface)

Setting default routes to point to the sub interface doesn't make a difference.

Thanks in advance.


3 Replies 3

Andrew Hickman
Cisco Employee
Cisco Employee

Hi Chaz,

It is not possible to disable the main interface as such (used for all untagged packets).

If you know that all traffic presented to the WAN interface will be tagged and to avoid the second DHCP request, you could just configure the main interface with a dummy static IP address (for example, if that doesn't interfere with your local addressing).

Ensure that the default route is selected for the sub-interface as you mention above.



Hi Andrew,

thanks for the update, what about with the 540?

We're looking at deploying these to mulitple sites, for SME's as part of my companies service portfolio.

But it's essential that one 1 interface be sending dhcp requests, and as it will be for multiple customers setting static's is neither scalable nor manageable.


Hi Chaz,

Configuring a static IP address on the main interface would be the only way to make it passive.  The address to use here could be the same for all routers, as technically it will never be used.

Ensure that you set the interface default route for the WAN interface to the new sub interface.

See the following as an example (I use private 192.168.. addressing in my lab.)