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TCP/IP communication question

Posted on 2015-01-26
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Do you know to what extent the network card is used in TCP/IP communication if the source and destination are the same server (itself). Does data make it to the physical NIC even though the communication isn't leaving the server?
Just wondering if the NIC driver and physical NIC are involved in the process. So if I have a server with a database on it, and the same server has the client piece on it, is the data making it to the NIC level even though this is internal only?

What I'm trying to determine is this:  Would the advanced TCP/IP settings on the NIC come in to play or not in this scenario where communication never leaves the server itself?
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Question by:ZabagaR
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giltjr earned 500 total points
ID: 40570564
No the traffic never makes it to the NIC driver.  You can see this by doing a wireshark packet capture and selecting the NIC assigned to the address in question.  You will see no traffic captured, because it never hits the driver.
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by:FarWest
ID: 40570588
as far as I know, when you don't use loop back IP which is 127.0.0.1, traffic will go to NIC
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by:nader alkahtani
ID: 40570592
You should use wireshark
When you ping loopback IP address 127.0.01 through 127.255.255.255  you now work with just software level without touch NIC, but if you ping host name or IP of your machine you will work with hardware.
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by:ZabagaR
ID: 40570631
Yes, you're right.  If I run a wireshark capture, and pick my databases port connection as a filter, I never get any data captured.
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by:giltjr
ID: 40570709
The first thing IP does when it needs to connect to a remote host is look-up the destination IP address in the routing table.  It then determines what it needs to do based on what the routing table says.

IP will see that to talk to IP address "X" it needs to send the data out the interface with address "X".  The 1st layer of talking to IP address "X" is the Windows IP stack.  The Windows IP stack sees that the destination is itself and never passes anything on to the NIC driver, thus it never gets to the NIC.

Depending on what NIC you have and how you have it configured a IP address on a local host is know up to 3 places:

1) The IP stack
2) The NIC driver
3) The NIC

Not all NIC's support knowing the IP addresses that NIC has assigned to it.
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