I would like to use my router's port forwarding capability to remotely access devices on my LAN such as IP cameras. I know that with an integrated modem/router this can be done - I have it working now.Will port forwarding work with a separate modem and router? The reason that I ask is that I believe most modems assign a private IP address to an attached router and not the public IP address. What I would like to know is:1- Do the CM500/600 modems have the ability to assign the public IP address to a router?2- will port forwarding still work when a router has been assigned a private IP address? I'm not a networking expert, but conceptually does the modem convert public IP+port x to private IP + port x?3 - when a router is configured to send the WAN IP address to a dynamic DNS service does it send it's assigned private IP address or does it have the ability to determine the public IP address and send it?Thanks

If you are on Time-warner network, they should assign you a public IP and for e.g. if you connect CM500 Cable modem with a R7000 Router, thr router will get Public IP and you will not have double NAT situation. I didnt know which ISP you had service with. some ISPs in asia provide private IPs to the users and it will create double NAT situation. I have not seen any ISP so far in US providing Private IPs but I have only worked with Comcasts and Time Warners. Not sure of smaller players.

CM500 and CM600 public or private IP address assigned to router?

3 Replies

vkdelta
NETGEAR Employee Retired
Dec 05, 2015
1- Do the CM500/600 modems have the ability to assign the public IP address to a router?
-- All the Cable modem I know allow public IP,
actually it gives whatever IP that is assigned by the ISP. the modem just acts as a bridge. If comcast want to assign a public, modem will give public to the Router (I know comcast does)

2- will port forwarding still work when a router has been assigned a private IP address? I'm not a networking expert, but conceptually does the modem convert public IP+port x to private IP + port x?
-- Nopes, if your ISP (I dont know which), does not have public, Port fwd is not useful. you can still use some applications such as teamviewer.

3 - when a router is configured to send the WAN IP address to a dynamic DNS service does it send it's assigned private IP address or does it have the ability to determine the public IP address and send it?
-- This is tricky. I need to check how this is handled in double NAT situation.
- Bitbanger76251
  Tutor
  Dec 05, 2015
  Thanks for the response vkdelta.
  
  My ISP is Time Warner. I am sure they assign a public IP. Today I use a modem/router combo and the config/status pages show a public IP address is assigned.
  
  So based on your resoponse that a modem-only device will act as a bridge, I am pretty sure that that getting rid of my modem/router combo and moving to a separate modem and router will result in the router being assigned the public IP and port forwarding working.
  
  You mentioned double NAT is tricky, I understand that, but I don't see that a double NAT would happen -- does the modem perform a NAT function? I assume that it doesn't.
  - vkdelta
    NETGEAR Employee Retired
    Dec 05, 2015
    If you are on Time-warner network, they should assign you a public IP and for e.g. if you connect CM500 Cable modem with a R7000 Router, thr router will get Public IP and you will not have double NAT situation.
    
    I didnt know which ISP you had service with. some ISPs in asia provide private IPs to the users and it will create double NAT situation.
    I have not seen any ISP so far in US providing Private IPs but I have only worked with Comcasts and Time Warners. Not sure of smaller players.

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CM500 and CM600 public or private IP address assigned to router?