Amos Jeffries wrote: > On 29/05/2012 6:12 p.m., Hans Musil wrote: > > Amos Jeffries wrote: > >> On 29.05.2012 08:13, Eliezer Croitoru wrote: > >>> hey there Hans, > >>> > >>> are you serving squid on the same machine as the gateway is?(wasnt > >>> sure about the DNAT). > >>> your problem is not directly related to squid but to the way that tcp > >>> and browsers works. > >>> for every connection that the client browser uses exist a tcp windows > >>> that stays alive for a period of time after the page was served. > >>> this will cause to all the connections that was served using port > >>> 3128 to still exist for i think 5 till 10 more minutes or whatever is > >>> your tcp stack settings. > >> > >> While that is true for the TCP details I think HTTP connection > >> behaviour is why that matters. For the TCP timeouts closure to start > >> happening HTTP has to first stop using the connection. > >> > >> iptables NAT only affects SYN packets (ie new connections). So any > >> existing TCP connections made by HTTP WILL continue to operate > >> despite any changes to NAT rules. > >> > >> HTTP persistent connections, CONNECT tunnels and HTTP > >> "streaming"/large objects have no fixed lifetime and several minutes > >> for idle timeout. It is quite common to see client TCP connections > >> lasting whole hours or days with HTTP traffic flow throughout. > >> > >>> > >>> On 28/05/2012 22:34, Hans Musil wrote: > >>>> Hi, > >>>> > >>>> my box is running on Debian Sqeeze, which uses SQUID version > >>>> 2.7.STABLE9, but my problem also seems to affect SQUID version 3.1. > >>>> > >>>> These are the importend lines from my squid.conf: > >>>> > >>>> http_port 3128 transparent > >>>> http_port 3129 transparent > >>>> url_rewrite_program /etc/squid/url_rewrite.php > >>>> > >>>> > >>>> First, I did configure my Linux iptables like this: > >>>> > >>>> # Generated by iptables-save v1.4.8 on Mon May 28 21:04:09 2012 > >>>> *nat > >>>> :PREROUTING ACCEPT [0:0] > >>>> :POSTROUTING ACCEPT [0:0] > >>>> :OUTPUT ACCEPT [0:0] > >>>> -A PREROUTING -i eth1 -p tcp -m tcp --dport 80 -j DNAT > >>>> --to-destination 10.17.0.1:3128 > >>>> COMMIT > >>>> > >>>> and everything works fine. > >>>> > >>>> But when I change the redirect port in the iptables settings from > >>>> 3128 to 3129, Squid behaves strange: My URL rewrite program still > >>>> gets send myport=3128, althought there is definitely no more > >>>> request on this port, but only on 3129. This only affects HTTP > >>>> domains that already have been requested before, i.e. with > >>>> redirection to port 3128, and it works fine again when I do a > >>>> force-reload on my browser. Also, things turn well when waiting > >>>> some minutes. > >>>> > >>>> I suppose there is some strange caching inside Squid that maps the > >>>> HTTP domain to an incoming port. > >> > >> No. There is only an active TCP connection. Multiple HTTP request can > >> arrive on the connection long after you start sending unrelated new > >> connections+requests through other ports. > >> > >> > >> What your helper was passed is the details about the request Squid > >> received. It arrived on a TCP connection which was accepted through > >> Squid port 3128. The fact that you changed the kernel settings after > >> that connection was setup and operating is irrelevant. > >> > >> > >> URL-rewriting is a form of NAT on the URL, but with far worse > >> side-effects than IP-layer NAT and is often a sign of major design > >> mistakes somewhere in the network. Why do you have to re-write in the > >> first place? perhapse we could point you at a simpler more standards > >> compliant setup. > >> > >> Amos > >> > > Thanks Amos. This makes things even clearer. Actually, I'd say that my > > problem is solved with the help of both of you. But well, let's have a > > look on my design. > > > > My goal is to build up an access control mechanism for my client > > machines to the internet. As long as a user has not yet logged in, his > > client box should be completely cut off the internet, not only HTTP. > > > > The login is done by a web interface. This is where I redirect the URL > > rewriting for any web traffic. After the user has logged in, the > > client's HTTP packets will be DNATed to the other squid port in order > > to be regularly proxied. I need the HTTP proxy for logging my users' > > HTTP requests. > > > > Since the users' client machines are out of my control, it is > > important for me that they don't need any special configuration, > > That's why the squid must run in transparent mode. > > Okay. As expected a design problem. The huge problem with transparent > intercept is that the browser is 100% unaware that the proxy exists. As > far as it is concerned the re-written splash page or redirect response > is the actual response to somebody elses domain name (google or your > bank for example). It has zero reason to think that a new TCP connection > is needed for followup requests. Just because the server of that page > replied Connection:close is no reason to expect Squid to pass the > closure on to the client (quite the reverse, Squid will go out of its > way to keep client connections open and re-used). > > > To fit in with your existing config that would be: > > acl port3128 myportname 3128 > deny_info http://your-login.example.com/ port3128 > http_access deny port3128 > > The full details and some other tricks can be found at > http://wiki.squid-cache.org/ConfigExamples/Portal/Splash > > This still hits the DNAT problems. I would suggest finding an > external_acl_type helper that accesses whatever database your login > script is recording client logins with. Using that as the ACL to deny / > bounce new clients to the login page. With that design you can authorize > a client on their initial request and continue using the connection > afterwards. > > NP: I recenty posted to the list a version of the external_acl_type > helper I use myself for exactly this type of portal setup. > > Amos Amos, I'm back. Thanks for your last posting. Your trick with acl, deny_info and http_access was a big help. As far as I understand, the external_acl_type helper needs to decide every few seconds whether a client is logged in or not. With some hundreds of clients, this means hundreds of database lookups per second. That's what I wanted to avoid by flipping the squid port when a user logs in or out, respectively. This way, I only have one iptables rule instead of multiple DB lookups. As far as the DNAT problem, I consider to simply run a "contrack -D" with appropriate -s and -d options from my login/logout script. 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