Router query to find out message destination


Thread Starter


When a router gets an IP address how will it find out the Source address from where the IP address has been received? Can anybody please tell me in a
detailed way how the router queries the Source Address of the IP.

Johan Bengtsson

That is quite simple (if I understand your question right) The from adress is a field in the IP-header as well as the to adress

/Johan Bengtsson

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The source iIP address is already contained within the IP packet, if I understand your question. If the router doesn't already have a table entry for the destination IP address, it sends it to the "default route", which is simply the IP address of another router. I add this because of your header including the word "destination".

These and other questions about how the Internet protocols work can be easily found on the web. Try putting in "RFC router" into the google engine and then do a little reading.


Willy Smith
Numatics, Inc.
Costa Rica

Hullsiek, William

The best reference for these types of the questions is Doug Comer's book on the Internet. There are block diagrams (and sample code !!!).

- Bill Hullsiek, MES Software Engineer