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spock2112's avatar
New Contributor

Double-NAT issue

I have a cable modem (not router) from Cox (Cisco DPQ3212) and I typically run with my own router (Nighthawk 7000). My problem is there is a double-NAT setup that is happening and this is blocking some services (e.g., Back to My Mac).

For example, my router gets an IP (68.111.XXX.XXX) from Cox and on my network it is Doing a traceroute to, I get:

1 ( 0.411 ms 0.254 ms 0.167 ms
2 ( 8.008 ms 6.342 ms 7.663 ms
3 ( 8.648 ms 7.138 ms 7.811 ms
4 ( 8.789 ms 7.540 ms 8.003 ms
5 ( 11.621 ms

So, the first is my private network (NAT 1) but the second there of is also a private IP meaning there is a second NAT going on.

If I remove my router and attach a single computer to the cable modem directly I get:
1 6 ms 8 ms 7 ms
2 8 ms 8 ms 8 ms []
3 8 ms 8 ms 8 ms []
4 11 ms 11 ms 11 ms

I hit that same machine. It's either in the Cisco cable modem (doubtful) or some network hardware of Cox's downstream.  (No, it's not something odd on the machine I'm testing with here - have checked on several)

So - how can I avoid the double-NAT?  Any ideas where it's coming from?

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  • ChrisL's avatar
    Former Moderator

    We actually set all of our customers up this way to save IP addresses. The 10 IP that you're referring to doesn't support NAT however so you won't see any double-NAT issues on your end. I suspect what you're experiencing is a port forwarding configuration issue with the router.

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