I am looking at the http-requests in BurpSuite. I see a field named as 'Host'. What is the importance of this field? What happens if I change this field and then send the request? If I change the host header field to some other IP then would the server respond back to this new modified IP?
To quote from https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Host :
The Host request header specifies the host and port number of the server to which the request is being sent.
If no port is included, the default port for the service requested (e.g., 443 for an HTTPS URL, and 80 for an HTTP URL) is implied.
A Host header field must be sent in all HTTP/1.1 request messages. A 400 (Bad Request) status code may be sent to any HTTP/1.1 request message that lacks a Host header field or that contains more than one.