tproxy - transparently re-direct HTTP requests to a HTTP cache.

tproxy [ -t | -p ] [ -f forced-url ] [ -s bind-port

[ -d ] [ -b bind-address ] [ -r runas-uid ] [ -a access-ip-address ] ] [ -l log-file ] proxyhost proxyport

tproxy accepts HTTP requests and forwards them to a cache host. If the HTTP request has been transparently re-directed, the URL is re-written so that the cache host knows what web server to fetch the document from. Tcp_wrappers is used to provide host access control.

The proxy-cache host's address and port are given by proxyhost and proxyport.

-t

Operate in a fully transparent mode. Instead of connecting to a proxy and sending a re-written URL, connect only the intended destination and send the real URL. This option can be used to allow tproxy to operate as a HTTP gateway (or proxy) on a firewall.

-p

Operate in proxy only mode. Normally if the connection to the proxy fails, tproxy will try and connect transparently to the intended destination. However for some sites this will never work and it is better to simply fail the connection.

-f url Force all accesses to be sent to the specified URL. tproxy checks for accesses that are referred by this forced URL and allows then to pass. This allows images on the forced URL to work.

-s port Run as a server and bind to the specified port. Alternatively tproxy may be run from either inetd or a program such a tcpserver. In these cases this options is not given.

-d

When running as a server, do not background the daemon. Usefull when tproxy is started from inetd or from the supplied tproxywatch program.

-b ipaddr Bind to the specified IP address. When run as a server tproxy will not accept requests sent to any other address when the host has multiple addresses.

-r user Run as the specified user. The user must exist in the /etc/passwd database so that its uid and gid can be obtained.

-a access-ipaddr Provide an IP address, network, sub-net, or super-net to allow access. May be specified more than once. If the host portion of the address in non-zero then the address refers to a host, otherwise it is assumed to refer to a network. The number of bits may be given in CIDR notation to specify a sub-net or super-net.

-l log-file Log all accesses to the specified file. The logfile will indicate if the request was done transparently, it was done without DNS activity, or it required DNS activity.

tproxy is not an all-in-one transparent proxy solution. It requires support from the operating system, and configuration from the system administrator, to transparently capture HTTP requests.

tproxyrun provides an example script to add firewall commands and start tproxy running. It currently supports FreeBSD-3.x and various versions of Linux. See the environment variable definitions at the top of the file.

tproxywatch provides a mechanism of ensuring that tproxy is re-started should it fail. Whenever tproxy exits an email is sent to the root account and then tproxy is re-started.

FreeBSD-3.x provides two methods of transparently capturing packets. The first is ipfw(8) using the following example configuration.

ipfw add 1000 allow tcp from 192.168.1.1 to any 80

ipfw add 1001 fwd 192.168.1.1,8081 tcp from any to any 80

The second is ipnat(1) using the following example configuration. Note that a rule is required for every interface you wish to transparently re-direct for.

rdr ppp0 0.0.0.0/0 port 80 -> 192.168.1.1 port 8081

Linux provides the same mechanism with either the ipchains(8) command, kernels 2.1.x and up, using the following example configuration.

ipchains -A input -p tcp -d 0.0.0.0/0 80 -j REDIRECT 8081

Or the ipfwadm(8) command, kernels 2.0.x, using the following example configuration.

ipfwadm -I -a accept -P tcp -D 0.0.0.0/0 80 -r 8081

hosts_access(5), tcpserver(1), ipfw(8), ipnat(1), ipfwadm(8), ipchains(8)

Written by John Saunders <john@nlc.net.au>

Copyright 1998, 1999, 2000 NORTHLINK COMMUNICATIONS PTY LTD. All rights reserved.