Cisco2821 router connecting to Verizon Router/switch/modem

[-Lastshad0w-]

I just want to know if I'm on the right track.  I am connecting  Cisco2821 router to a port on an all in one "verizon modem/router/switch".  Someone told me I have to enter a default route pointing to the verizon all in one.  However, I don't think that will work because my internal IP addresses are 172.16.0.0 and don't know how Verizons router will route those packets back to me if it's not aware of my networks.  I am assuming I will have to reserve an IP address on verizons router and statically assign it to mine and then enable NAT?  I am not home to try this but will be getting back home in a few days so I can try it.  If you have any input it would be much appreciated.  Thank you in Advance.

[Seb Rupik · Accepted solution]

Hi there,

As you point out the Verizon device will not be aware of the subnets being routed by your 2821. If the Verzon device can run a dynamic routing protocol and form an adjacency with the 2821, or allow you to configure static routes directing traffic to the 2821, then that would solve your issue.

We'll assume that it can't do either. You best bet is to configure dynamic NAT on the 2821 'outside' interface (the one connecting to the Verizon device), to translate all of your outbound traffic from internal subnets.

I wouldn't worry about reserving an IP on the Verizon for the 2821. The NAT setup will work fine with a DHCP address.

cheers,

Seb.