HTTP header "Via:1.1 nc1 (NetCache NetApp/6.0.5P1)" stops IIS6 gzip compression - http-headers

Question

The request I sent is accept gzip but the response is not compressed, instead, I received some header
Via:1.1 nc1 (NetCache NetApp/6.0.5P1)
I guess this is to do with my ISP since it works perfectly on my home computer.
Any idea how to get the response compressed?
Request header
GET /test.aspx HTTP/1.1
Host this.is.example.com
User-Agent Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3 (.NET CLR 3.5.30729)
Accept text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language en-us,en;q=0.5
Accept-Encoding gzip,deflate
Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive 300
Pragma no-cache
Cache-Control no-cache
Response header
HTTP/1.1 200 OK
Date Mon, 01 Dec 2008 19:53:40 GMT
Content-Length 6099
Content-Type text/html; charset=utf-8
Cache-Control private
Server Microsoft-IIS/6.0
X-Powered-By ASP.NET
X-AspNet-Version 2.0.50727
Via 1.1 nc1 (NetCache NetApp/6.0.5P1)
Expires 0
Cache-Control no-cache
// I expect content-encoding to be gzip here
Thanks in advance.

Answer 1

There's no mechanism to force response compression. Accept-Encoding: gzip only tells the webserver/proxy that it MAY compress the response, not that it MUST encode the response. There are many webservers and proxies that don't support gzip out of the box, or have it configured off by default.
The Via header that you found is frequently inserted by proxies that connect to the intended webserver on your behalf, and is informational. It's unrelated to your compression woes.