two routers question

[Ian Stephen]

A question for those who know networking

I recently got VOIP (Vonage) at home, but I like the firewall in my old
router so wanted to have

- cable modem connected to VOIP router
- telephones connected to VOIP router
- old router connected to VOIP router
- computers connected to old router

Everything I found on the web said to disable DHCP in the second router
and plug the cable from the VOIP router into a regular port, not the wan
port, on the second router to make this setup work.

I wanted DHCP enabled in the old router because I'm guessing it needs
DHCP enabled for its firewall to work.  It seemed to me that the second
router wouldn't know the difference between being connected to the cable
modem and being connected to the VOIP router, so I just went ahead and
plugged everything in that way.

VOIP router has DHCP enabled using addresses in a range of
192.168.15.xxx.

Old router has DHCP enabled using addresses in a range of 192.168.2.xxx.

It all seems to work fine.  Was the advice I found via Google wrong or
have I done something wrong that I just haven't noticed yet?

Thanks,
IanS