Lighttpd

found that when use .html/.htm as ssi extension like this:

...
static-file.etags = "enable" 
etag.use-inode = "enable" 
...
ssi.extension = ( ".htm", ".html", ".shtml" )
...

lighttpd not generate ETag & Last-Modified headers any more:

HTTP request sent, awaiting response...
 1 HTTP/1.0 200 OK
 2 Content-Type: text/html
 3 Content-Length: 111099
 4 Date: Wed, 19 Dec 2007 09:41:37 GMT
 5 Server: lighttpd
 6 X-Cache: MISS from cache-198
 7 Connection: keep-alive
200 OK

the squid servers had to renew the html/htm file every time be accessed,
so bad...

wrote a patch to solve this problem, now work like this when enable ssi
on html/htm files:

HTTP request sent, awaiting response...
 1 HTTP/1.0 200 OK
 2 Content-Type: text/html
 3 ETag: "4289947051" 
 4 Last-Modified: Tue, 18 Dec 2007 08:33:38 GMT
 5 Content-Length: 110893
 6 Date: Tue, 18 Dec 2007 23:52:50 GMT
 7 Server: lighttpd
 8 Age: 35660
 9 X-Cache: HIT from cache-198
10 Connection: keep-alive
200 OK

hope it's helpful to others

-- zihua.ye