Rommel Rodriguez Toirac <romme...@nauta.cu> wrote:
> First, I live in Cuba and here the access to Internet is a little different that in the rest of the world. Let say just different.
> My ISP (in my case the national network level) give the ranges 172.16.120.0/24 to my network and from 172.16.121.0/29 to the rest of my 10 municipal networks.
> The IP given to my router is 172.16.120.254 and all other routeres in my municipal networks are in 172.16.#.# range too.
> OK 192.168.0.0/16, 172.16.0.0/12, 10.0.0.0/8 are PRIVATE network address but I don not have any PUBLIC address.
> Our network work like this way, just in PRIVATE network address and our routers are configured to use this.
Well then, in that case you cannot have any services accessible from the internet - UNLESS the ISP allows you to configure port forwarding rules in their system to allow connections to a public IP to be forwarded to one of your systems.
> Why I can make possible the communication using just IP address and why not using PCs names or alias?
OK, more DNS issues here.
For a device to get an IP address from a name, it must ask a resolver that either knows the answer, or knows how to find the answer. If your systems are configured to use your own server (and nothing else) for DNS resolution, then they should be able to find systems by name. But that doesn't scale if you are wanting to access these systems from outside of your own network.
When I do a simple test, I find that gob.cu doesn't appear to be a valid domain :
> $ dig +trace ftp.gtm.onat.gob.cu
>
> ; <<>> DiG 9.8.5-P1 <<>> +trace ftp.gtm.onat.gob.cu
> ;; global options: +cmd
> . 3600 IN NS FWDR-9.FWDR-6.FWDR-159.FWDR-212.
> . 3600 IN NS FWDR-10.FWDR-6.FWDR-159.FWDR-212.
> ;; Received 177 bytes from 192.168.1.254#53(192.168.1.254) in 26 ms
>
> cu. 584 IN NS cu.cctld.authdns.ripe.net.
> cu. 584 IN NS ns2.ceniai.net.cu.
> cu. 584 IN NS ns.dns.br.
> cu. 584 IN NS rip.psg.com.
> cu. 584 IN NS ns.ceniai.net.cu.
> cu. 584 IN NS ns2.gip.net.
> ;; Received 428 bytes from 212.159.6.9#53(FWDR-9.FWDR-6.FWDR-159.FWDR-212) in 996 ms
>
> cu. 3600 IN SOA ns.ceniai.net.cu. cu-tech.ceniai.inf.cu. 2017102701 3600 1800 1209600 3600
> ;; Received 106 bytes from 204.59.1.222#53(ns2.gip.net) in 22 ms
What this means is that my resolver went to the root servers and asked the question "what's the IP for ftp.gtm.onat.gob.cu ?" - and got the answer : "I don't know, but I can tell you that these DNS servers handle the .cu zone".
My resolver then went to one of these servers and asked the same question - and got the answer "we don't know anything about it". As a result, it's impossible to resolve anything ending in gob.cu because the DNS servers for .cu don't seem to know anything about it.
Thus, nothing will be able to resolve addresses unless they've been configured to use your DNS server.
> See the test maded from a municipal server.
> When I try to connect to FTP server on my network using IP number the connection are success, but when I use the alias ftp.gtm.onat.gob.cu never connect.
>
> C:\Windows\system32>ftp
> ftp> open 172.16.120.1
> Conectado a 172.16.120.1.
> 220 ONAT Guantanamo, FTP.
> Usuario (172.16.120.1:(none)): anonymous
> 331 Please specify the password.
> Contraseña:
> 230 Login successful.
> ftp>
>
> C:\Windows\system32>ftp
> ftp> open ftp.gtm.onat.gob.cu
> ftp>
OK, that's consistent with not being able to look up and address (I think, I'm not that familiar with Windows).
> I try a nslookup and (I guess) the answer are good.
>
> C:\Windows\system32>nslookup ftp.gtm.onat.gob.cu
> Servidor: gtm08.cai.gtm.onat.gob.cu
> Address: 172.16.123.11
>
> Respuesta no autoritativa:
> Nombre: gtmft.gtm.onat.gob.cu
> Address: 172.16.120.7
> Aliases: ftp.gtm.onat.gob.cu
Bear in mind that nslookup may use different servers to what other components of the system are using - and hence may give different results. This is an area of Windows that I don't know much about.
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