How Outlook mail server is reachable from Home over Internet without VPN

[ashish7aditya]

Dear Experts,

Few queries & need your support to understand same.

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• I understand that over the internet, no two private nw can communicate with each other without creating a VPN (I.P tunnel). But I noticed a case where PC is on public Nw (ex- internet at Home) & still VPN connection is not required to access outlook mail server. How is it possible?
• Further if someone can explain me what RPC(remote Procedure Calls) do & means exactly? I went through Wikipedia but still can't understand the concept of RPC .. Basically where & what for it is used ?

Many Thanks!

Ashish JAIN

[Jon Marshall]

Ashish

If you are not using a VPN then your outlook server must be using a public IP address and is also probably running SSL to encrypt the traffic.

An RPC allows a program or programmer to call a procedure on the local computer which is then typically executed on a remote computer. Basically it means that the programmer does not need to understand all the network details that are involved with making that happen.

So they simply make the procedure call as if it was on the local computer but it is actually executed on a remote computer and the results returned to the local computer.

Jon

[ashish7aditya]

Hi Jon- Thanks for the feedback.. However Server is still on private network and reachable through PC on public network without VPN.

[Jon Marshall]

You cannot route to a private IP address across the internet.

Are you sure there is no VPN ie. when you fire up your web browser it may be using a clientless VPN to make the connection to the server.

Jon

[ashish7aditya]

Thanks Jon,

Regarding Clientless VPN, I will recheck with IT team & will get back. I can't find any application in this regard on my machine.

Further I have one more doubt i.e.

If we can create static NAT for mail server on router near the edge of an organization and we create NAT overload on home router, do we still need VPN to access mail server?

I have attached one drawing in this regard . As per my understanding in such cases VPN tunnel shouldn't be required to reach mail server . Your comments please.!

Best Regards!

[Jon Marshall]

You wouldn't need a VPN if both ends were using public IP addresses but you would need SSL to encrypt the traffic.

Jon

[ashish7aditya]

Meaning VPN will not be required if both end routers have NAT enabled but I should have SSL for security reasons .Correct ? Did I understood correctly?

So, in my original query, can it be one of the possibility that NAT is enabled on either end router & because of this I can access mail server through internet without VPN.?

Correct?

Best Regards!

[Jon Marshall · Accepted solution]

Yes you understood correctly for both.

Jon