Is it different in case of INVITE or REGISTER messages and UDP,TCP,TLS transport?
There is a nathelper module that allows to test if the UAC is behind NAT with function nat_uac_test() help. But it is not clear ho to use it in my case?
If the UAC is behind the NAT and the NAT router does not act as SIP ALG (it does not change the content of SIP traffic), then the private IP address of UAC should be in Contact header address and in the last Via header. You can get the Contact header address with:
$(ct{tobody.host})
The address of the last Via header should be:
$sel(via[-1].host)
In the INVITE, the private IP of UAC should be in SDP body as well.
Related
Based on my knowledge , I believe following statements are true.
Router can only redirect packet and can interact upto network(internet layer) only.
NAT maps the private ip to public ip. It uses a NAT table in which source private ip is mapped to public ip and also source port is changed with new source port.
My question is regarding NAT function for port . How NAT , that works in router can change something that relates to transport layer(port)?
i.e when the private system sends the source port , how NAT is able to change it with new port before sending it to internet.
I am missing something or maybe I am wrong somewhere . Would appreciate the help.
Thanks
NATs intercept outgoing IP packets (including UDP and TCP) from nodes on the NAT's internal network and can modify the source IP and source port in the UDP and TCP header in place. It will update other fields in the header as well (i.e. checksum).
Similarly, for incoming packets, the NAT will change the destination IP/port after finding an entry in its port mapping table that was created from a previous outbound packet or connection.
As to "how" - it just does. It literally reconstructs a new UDP/TCP/IP header using the exact same payload of what it received. The NAT is registered as the gateway device on the LAN, so all packets bound for the internet will be sent to the NAT's MAC address - if what you are wondering is how the NAT captures the packets to begin with.
Let's say that I have a home network of 5 computers. They all share the same external IP address.
Suppose a machine that is outside the network sends a request (as a client) to one of the 5 computers (this computer will be the server) in this home network. It sends its message to the external IP address. Then, how does the router know to what computer in the home network the message has to be routed to?
Typically when you talk about NAT, there are two main “flavours” - Source NAT & Destination NAT. There is another function called “PAT” (or Port Address Translation).
Source NAT is utilised when all your 5 computers are trying to reach out to the public (Internet) network. At this point your 5 computers get MASQUARADED with your public IPv4 address.
Destination NAT is what you’re asking for. In this case, you must configure your router/firewall (device that holds your public address & maintains your public connection) to “REDIRECT” or “DNAT” all incoming packets destined to a specific application (or port). For instance, if you have an HTTP server running on your private network server with address 10.0.0.3, you simply instruct your router to send all (or selective) TCP packets that have been sent to the public IP on ports 80/443 & send those to 10.0.0.3.
In DNAT scenario you must explicitly instruct your router/firewall about every type of expected, incoming connection. Another example can be that same public address is been used for SMTP server and thus sending all TCP packets received on port 25 to be sent to local server 10.0.0.4 this time. And so on and so forth
That’s in short how it works.
Network Address Translation (NAT) allows a single device, such as a router, to act as an agent between the Internet (or public network) and a local network (or private network), which means that only a single unique IP address is required to represent an entire group of computers to anything outside their network.
ADDRESS TRANSLATION (NAT) OVERLOAD allows your 5 computers to communicate with your router. Each computer has unique private IP address.
When computer1 tries to communicate with website, it sends packet to router.
Router replace the private IP address (example: 192.168.1.1) with single public IP address (example: 205.65.45.100) but uses same source port number (for example Port 5000) which is used by computer. It won’t change the source port number. And Router maintains entry in NAT table.
The reply from the (web server) internet arrives at your public interface of your router.
The router accepts packet and check the destination port entry. With the help of the NAT table, your router understands that it belongs to computer1. Router changes single public IP address (example: 205.65.45.100) with your internal private address (example: 192.168.1.1) and your computer receives it.
This process is applicable for all 5 computers.
Above scenario is only applicable if your computers act as a client. If your computer acts as a server then the solution is “Port forwarding”.
Port forwarding is needed when a machine on the Internet needs to initiate a connection to a machine that's behind a firewall or NAT router.
Refer video for detail information.
https://www.youtube.com/watch?v=-K6jMYBfuIY
I'm running mirth on Azure VM (Windows Server 2016) and trying to get HL7 messages from Meditech. Not really familiar with tcp/ip concept so help is appreciated here. When Meditech sends HL7 messages to my server (VM), how should I configure the setting in mirth's channel?
For example, in Listener Settings panel,
1.Select Specific interface and put my VM's public ip address.
2.Put port number I set in inbound rule in Local Port
or do I put Meditech's ip address and port number in Listener Settings?
TCP/IP is pretty simple. From the sending system, you specify the destination IP address and port # that you want to send to. From the destination system, you set up your listener to run on a specific port #. In Mirth you can choose to accept messages from any IP (All interfaces) or a specific IP address (specific interface) in the TCP Listener Settings:
So to address your specific example, it sounds like you want a message to go outbound from Meditech to your Mirth instance on an Azure VM. In Meditech, you would enter the Azure server's IP address and port # that you specified in Mirth. In Mirth, you can leave it open to the world and select "All interfaces," or specify your Meditech interface engine's IP address in "Specific interface."
One final thought.. I have never played around with Azure, but I'm sure there are some security settings. (hopefully it is behind a firewall of some sort) You may need to explicitly allow traffic from your Meditech interface engine's IP. If you need further help with that, I would post a new question and tag it under Azure.
I'm able to open the website being served on port 4568 on 127.0.0.1 (localhost) and my private ip address, but I can't seem to do so on my public ip address. I've tried to access the website by typing :4568 after my public ip like I did for my localhost and private ip.
Is it possible to open a site running locally on my computer through my public IP? If so, how? If not, why not?
NOTE: I'm not exactly clear what tags are appropriate. Feel free to add or remove any you deem inappropriate.
You are likly behind a NAT. What this means is that your public IP address and private IP address are not necessarily mapped to each other fully. To explicitly map your application to your public address, try the following:
Go to your modems management page
Look for a 'Port Forwarding' tab (might be under an advanced or
router menu)
There will probably be two or three field to enter:
The port on the public ip address to forward traffic from
The IP address to forward traffic to (your private IP)
(might be there) The port to send it to on the private IP
Assuming this works, all traffic going to your public IP address on that port will now go to your private IP address.
WARNING This is a simple rule and everyone on the internet can now access that port
Also make sure your web server is listening on 0.0.0.0 (all IP addresses) and your local firewall is allowing remote connections on the port in question.
Ignoring other possiblities such as Request.ServerVariables["HTTP_X_FORWARDED_FOR"], does Request.ServerVariables["REMOTE_ADDR"] gives me the "principal" IP of the client?
I'm talking about the IP that made the actual TCP connection.
Will ServerVariables["REMOTE_ADDR"] always be the "real" IP address of the remote endpoint?
Just to clarify: Even if it's a proxy who made the real TCP connection I'd like have its IP, and not a forwarded one.
Yes, except if its been through a NAT firewall. A NAT firewalled address would be masquerading many 192.168.x.x or any other private subnet behind a public IP address. So you'd be looking at the IP address of the NAT firewall (i.e. a Linksys Router or what have you).
Be warned that many cell phone carriers have HUGE NAT networks so they always look like they are coming from one or two public IP addresses.
The REMOTE_ADDR variable will be the IP of the system that directly connected to your web server to request the URL; so it would be the forward-most proxy server, if there is a proxy server.