Is the external IP of my wireless Router my WAN IP / Public IP address ? if not then what is it?

Question

This is my home network setup:

Internet ---> External IP (cable modem) Internal IP ---> External IP (wireless router) 192.168.20.1 ---> (laptop) 192.168.20.102

Am I correct to assume that the WAN IP / Public IP assigned to me by my ISP is at the external side of the modem or is it on the external side of the wireless router? I am guessing that the External IP of my wireless router has to be on the same subnet of the internal IP of my modem

Where do these 3 IP addresses go into my home network as shown above

• WAN IP / Public IP (static)
• WAN gateway (the static Gateway associated with WAN IP)
• Modem internal IP ( I found it to be 192.168.100.1 a Cisco DPC3008 )

I was thinking more like it goes like this:

Internet ---> WAN IP / Public IP (cable modem) WAN GATEWAY ---> External IP (wireless router) 192. 168. 20. 1 ---> (laptop) 192.168.20.102

Then on this assumptions I'm leaving behind modem internal IP, and External IP of the wireless router would have to be on the same subnet of the WAN gateway which is getting a bit confusing.

What I know for sure is that the External IP of my wireless router should be on a different subnet than 192.168.20.1 so that it can route the packets into another network which is in my case, the internet.

Here is the diagram:

Added by barlop

The item the OP describes as a (cable) modem, is a cable modem router.

Cisco DPC/EPC 3008 has one cable modem connector, and one ethernet port, and also, it is a gateway/router (the document I liked to describes it as such) So it's a cable modem router with one ethernet port. It's sold as a cable modem. (Note that Cisco also do the cisco DPC/EPC2325 which is sold as a gateway but is a cable modem router with multiple ethernet ports)

Additional Info: must read

just wanted throw out a bit of info to make sure everything is crystal, it might or may not sway your answers

1. Both WAN IP / Public IP (static) and WAN gateway (the static Gateway associated with WAN IP) are present on the WAN tab of the wireless router's admin page which is accessible at 192.168.20.1

2. On the Routing table of the wireless router's admin page, it shows that destination 0.0.0.0 of Netmask 255.255.255.0 is having the WAN gateway (above) as the determined Gateway using interface eth2.2

3. Doing a tracert WAN IP, yielded 1 hop/node

4. Doing a tracert WAN gateway, yielded 5 hops/node (nodes 2 to 4 are all request time out)

side note:

it felt odd that number 3 and 4 suggests that my home network setup is

Internet ---> External IP (cable modem) WAN GATEWAY ---> WAN IP / Public IP(wireless router) 192. 168. 20. 1 ---> (laptop) 192.168.20.102

the reason I thought of this is because tracert means that the packets are being pushed from the wireless NIC of my laptop going outwards into the next node/device

Solution

I really appreciate everyone's input though after further research I finally found a way to understand how my home network works, if someone could post the image I have created from visio in here http://postimg.org/image/qyp8ag54d/

In this setup the cable modem acts as a Network Bridge device which is responsible for making your Local area network as one with your ISP. The static WAN Gateway address provided to you by your ISP is sitting at the ISP's CMTS/UBR network interface (catV segment) which is given a public IP address in the 10.x.x.x.x or 172.x.x.x.x range as a means of sending packets on your cable modem that as a DHCP client has requested a private IP address in that same range

Comments

[amdc]

still quite lost.. I have known that the cisco DPC3008 could be originally installed without a router in between and directly connects to your computer or laptop by ethernet which means the cable modem itself assigns an IP address to your computer's MAC to communicate with it , whereas in my setup has been with a router in between ever since. Can somebody confirm that my router does acquire its external IP from the modem ? if it is so, would it be in the 192.168.100.0/24 subnet?

[amdc]

on a (cable modem)---(computer/Laptop) setup, regarding with the cable modem assigning an IP to the computer/laptop , im not sure if it's the WAN / Public IP or in the range of 192.168.100.0/24, but to think of that as far I know the cable modem does not have a dhcp server but it might be able to give 1 private IP..not sure though

[barlop]

Modems don't assign IPs. And modems don't have IPs. These devices are boxes with particular functions. You have to figure out what functions these boxes have. From my experience of cable modems , cable modems tend to just be cable modems, not having additional functionality.

[barlop]

Modems don't assign IPs. And modems don't have IPs. These devices are boxes with particular functions. You have to figure out what functions these boxes have. Usually cable modems tend to just be cable modems, though cisco does cable modem routers. Though it could be a current/new thing that devices that function as cable modems nowadays tend to or often function as routers too. Regardless. DHCP servers hand out IPs. Routers have IPs, modems don't. One must isolate the function one is speaking about, within the internet device.

[amdc]

Hi, when I do route print command on my laptop it is the Internal IP of the wireless router which is shown as my gateway - 192.168.20.1 , by the way just to let you know, the WAN gateway which you believe to be on the Internal side of the cable modem (which id like to think it is so) is not in the range of 192.168.100.0/24 network, it is slightly different than my WAN IP, differing only by the last octet (x.x.x.1) .

[fragwürdig]

I am sorry, in my third point I meant "wireless router" and wrote "laptop". But I am confused as you are. Can you print the full output of your route tracing command (tracing the route for example to your public IP or google.com or so)?

[amdc]

oh i see im getting to your point,

[amdc]

i think its making sense that the WAN gateway is my cable modem's internal IP and also is my wireless router's gateway as it can be shown as the gateway in my router's routing table when using the admin tool at 192.168.20.1. I feel I'm getting quite close to the real thing.. thanks, but who assigned the 192.168.100.0/24 subnet for my wireless router? My Cisco DCP3008 cable modem doesn't have a dhcp server

[amdc]

Ok wait does it mean that my cable modem does have a dhcp server? cause i entered the admin tool for DCP3008 using 192.168.100.1 and there are no relevant links/buttons to a DHCP server , just status and log off, well on the status it says DOCSIS Downstream Scanning: Completed DOCSIS Ranging: Completed DOCSIS DHCP: Completed DOCSIS TFTP: Completed DOCSIS Data Reg Complete: Completed DOCSIS Privacy: Enabled

[qasdfdsaq]

Cable modems shouldn't ever have DHCP servers. Routers have DHCP servers.

[barlop]

You write "subnet between modem and router." <-- sounds like you've got your layers mixed up, but that you know better and could be more correct in your terminology

[barlop]

You write "the Class C private 192.xxx.xxx.xxx area." <-- You're aware classes haven't been used in about 20+ years, right? CIDR(classless....) was introduced long ago and IANA no longer restrict themselves to the subnets decreed by the classful system. And routers no longer use the classful method to determine subnet mask. And it'd always have been a bit misleading to talk of the private addresses as being classful, because the subnet masks of the private addresses don't/have never, corresponded to the classful system

[barlop]

@qasdfdsaq seriously? Technically, routers don't have DHCP servers any more than modems do.. Though it is common that the boxes described as Routers also have a DHCP server. It is also not uncommon that the boxes described as modems are routers too, and that they have have DHCP server too. These are boxes.. with functions. Router is a function. Modem is a function. DHCP server is a function. Granted though, that when they have a DHCP function they tend to have a router function. And when they have a modem function they may or may not have a DHCP function.

[goblinbox]

Subnetting has to do with routing packets from device A to device B on a network; the layer model talks about the physical functions of moving those packets up and down the stack on an individual device. Different things. :)

[goblinbox]

Technically true but irrelevant. Class terminology is still used in Cisco courses today (because you have to learn class before you can learn classless), and in this context the OP obviously means "a network of 256 IPs", not "the number of bits used for the network portion of the IP".

[barlop]

You write "Subnetting has to do with routing packets " <-- And guess what layer that/IP/Routing is. It's Layer 3. And guess what layer modems don't deal with - layer 3. Guess what modems don't deal with - routing. So when you're saying "subnet between modem and router." and "Subnetting has to do with routing packets" you're obviously not realizing that modems don't operate at layer 3.

[goblinbox]

Um. The modem under discussion is also a router. The little network between the modem and the wireless router can be called a subnet without offending most people or even being dreadfully inaccurate. Not sure what your point is.

[barlop]

@goblinbox I'm all for learning old stuff but know that it's old and not done anymore. Cisco courses are known to be wrong on this issue, and hence students of cisco are often corrected on it, and are surprised to hear that classes aren't used anymore. And the OP didn't use the term class, this answerer introduced the incorrect terminology of Class.

[amdc]

Hi Goblin box I added some info on the original post please have a look

[amdc]

Hi fragwurdig is there anyway to know if what you said on your update on no.2 is actually happening on my home network setup?

[amdc]

Hi Christopher and Barlop I updated the original post please have a look

[qasdfdsaq]

@barlop: A router is a device. A modem is a device. A DHCP server is a function of routers. It is not a function of modems. You may be confusing "routing" with "router"

[barlop]

@qasdfdsaq When I said router is a function,I don't mean grammatically,if I were 2b grammatically accurate,router isn't a function, it's a noun for the function -"routing".There is only one function of routers,that is,routing.u can turn off a rter's DHCP server and it's still a Router,it's still Routing.A Router can b built without a DHCP server and it's still a Router.(apparently the wired cisco 2500 series which were as recently as 10+ yrs ago,were pre IOS-the cisco router OS- having DHCP, and cisco enterprise routers disable dhcp by default) .U can build a linux router with no DHCP server