Sending CURL request with custom IP

curl

Shouldn't it be possible? Let's assume I don't need a response, I just want to send a request. Shouldn't we be able to alter tcp/ip headers, because our computer sends it? I am probably missing something, just really curious, learning about it in the uni.

Best Answer

You can using the -H/--header argument:

You could spoof your ip address:

curl --header "X-Forwarded-For: 192.168.0.2" http://example.com

Example:
client 

$ curl http://webhost.co.uk

web host 

$ tailf access.log | grep 192.168.0.54   
192.168.0.54 - - [10/Nov/2014:15:56:09 +0000] "GET / HTTP/1.1" 200 14328 "-"   
"curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.14.0.0 zlib/1.2.3   
libidn/1.18 libssh2/1.4.2"

client with ip address changed 

$ curl --header "X-Forwarded-For: 192.168.0.99" http://webhost.co.uk

web host 

$ tailf access.log | grep 192.168.0.99  
192.168.0.99 - - [10/Nov/2014:15:56:43 +0000] "GET / HTTP/1.1" 200  
14328 "-" "curl/7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.14.0.0  
zlib/1.2.3 libidn/1.18 libssh2/1.4.2"

man curl

 -H/--header <header>
              (HTTP)  Extra header to use when getting a web page. You may
              specify any number of extra headers. Note that if you should add
              a custom header that has the same name as one of the internal
              ones curl would use, your externally set header  will  be  used
              instead  of the internal one. This allows you to make even
              trickier stuff than curl would normally do. You should not
              replace internally set headers without knowing perfectly well
              what you’re doing. Remove an internal header by  giving  a
              replacement without content on the right side of the colon,
              as in: -H "Host:".

References:

Modify_method_and_headers

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