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DDNS cant work for GPRS dynamic IP? Easy to answer noob question

2K views 1 reply 2 participants last post by  JohnWill 
#1 ·
Hey guys, I am from a engineering background, I have some fuzzy networking concepts probably need to clear up. If you guys can bear with some simple noob questions....:rolleyes: Advance thanks.

If I want to dial in via GPRS a remote wireless modem with dynamic IP, I need to use DDNS (dyndns.com), no? I am unable purchase GPRS static IP for the modem because it cost $600/month in my country so my only option is using DDNS.

However, I think the above method will not work base on my present understanding:

1. I got the below ordinary USB wireless modem people normally use for internet browsing.



I plug the usb wireless modem to my laptop. I go to whatismyip.com, it shows the IP address 220.255.7.139. I type ipconfig, it shows the IP address is 119.234.164.229! So why is the two Ip address shown is different? I as a noob thinks that whatismyip.com is showing the gateway address of my usb modem gprs network visible to the internet. And ipconfig is showing the ip address of my usb modem inside the GPRS APN but not visible to internet. Is my understanding correct at this point?



2. I then unplug and plug the usb modem, check the ipconfig, and repeat. I notice each time the Ip address shown in ipconfig is different. This shows that the modem ip inside the GPRS APN is a dynamic IP, not a static IP. Is my understanding correct for point 2?



3. I unplug and plug the usb modem, and check whatismyip.com. I notice the each time ip address shown in whatismyip.com is different. This shows that my usb modem gateway is appearing as a dynamic IP address in the internet, not a staic IP as one noob would intuitively think. Is my understanding correct for point 3?

4. So below is my overall understanding of my usb modem core GPRS network architecture. Is my conceptual understanding correct?



5. So now I have a Sierra Wirelessmodem RavenXT, which manual claims that my local office PC software can find the remote RavenXT inside the GPRS APN with the help of DDNS (dyndns.com) without the need for static IP. Well from my understanding, DDNS would only work if the RavenXT has static IP inside the APN. If the RavenXT has dynamic IP inside the APN , from my understanding above, the DDNS cannot find the dynamic IP in the GPRS APN, because dyndns.com is in the internet world, there is no DDNS in the GPRS APN. So the DDNS concept generally would not work if the office PC is to find a remote modem wirelessly and the IP addresses inside the GPRS APN are dynamic.

But however DDNS for Sierra Wireless Raven XT is used extenstively in USA. So I estimate that USA's GPRS APNs generally assign static IP inside its private network, unlike the GPRS networks my country. Is my understanding correct? What is your experience of this?:D

 
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#2 ·
Actually, What's My IP would be showing you your public IP address. The 119.x.x.x address is apparently some kind of internal translation happening within your network.

I don't see why DynDNS wouldn't work for you, have you actually tried it?
 
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