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Proxy
Server
- HTTP &
FTP proxy
- Caching
- Setup
- Autodialling
- FTP-gate
- TCP and UDP
link mapping
- DNS
proxy
- Bind
setup
| Eserv뭩 built-in set of proxy servers allows
LAN users to work practically with any software for the Internet. A
list of tested applications along with setup instructions for their
in-Eserv operation are kept up on the 'client's program setup' page
of this documentation. The profile has setups for most of the
widespread programs for all types of proxy. Programs not described
on the page can be set up similarly. (24.11.1999) | |
| Eserv뭩 HTTP and FTP proxy make browser
inquiries for obtaining information from the Internet. The proxy
server is started on a computer provided with direct access to the
Internet, and the browsers on all other computers in the LAN are set
up to receive information through it.
HTTP is the basic protocol used for transfer of hypertexts,
images and other files in the Web, and is therefore the basic
protocol for browsers. FTP is an older file transfer protocol used
mainly in file archives. Browsers work with either of these
protocols through a proxy working under the HTTP protocol.
(03.08.1999) | |
Eserv can make HD copies of already received
files, and, if a file is inquired repeatedly, give it to the Eserv
browser without having to download it from the Internet. This
facility is called caching. There are several modes of proxy server
checking whether a file has to be downloaded once again or it can be
retrieved from the cache:
- Minimal channel load: not to check at all.
- To check only if the page is older than a set number of days;
it is possible to set e.g. 1 day, and then Eserv will repeatedly
download the resource not more often than once a day.
- Standard mode: the use of TTL and 밿f-modified?inquiry (the
way of communication between the proxy and Web servers offered by
the HTTP/1.1 standard).
- Caching switch-off (operation in the Eserv/1.* mode).
If a file has not been received thoroughly by the proxy
server, it is not copied to the cache.
Dynamic pages formed by Web servers on inquiries issued in the
course of filling by users various forms are not cached. For
instance, a page given by a search system in reply to key words
suggested by a user will not go to the cache. (03.08.1999) | |
| The HTTP proxy serving HTTP and FTP browser
inquiries is set up in the section ProxyServer. It is possible to
select the caching mode, the mode parameters and the directory where
the proxy cache will be located. The procedures for changing these
parameters are described in the context help of the Setup Program.
The section ProxyServer/BlackListURL is used for compiling a list
of external Web servers access to which should be limited by a proxy
server. In cases of application of user browsers to these pages, an
inquiry to call the user name and password will be issued, and
access will be granted only if the user belongs to a privileged
group. For more information on the user authority control system see
6.9. It is possible to restrict access to individual directories or
files on Web servers. To add servers to the black list, go to the
section BlackListURL, enter the fragment URL and click the Add
button. If the proxy server finds in the inquiry one of the lines
included in this list, it will restrict access.
This proxy defaults to Port 3128. The same port is used by the
built-in HTTP Server (Web server). It automatically tells proxy
inquiries from usual applications to the local server. The port
number is set in the section WebServer. (03.08.1999) | |
| Eserv can be set up for automatic dialling on
proxy inquiries. If the Internet is accessed via modem, and at the
moment of a browser application to a proxy server no modem
connection is established, Eserv can automatically dial and make a
transparent inquiry for the user, just as if connection had already
been established. Dialling is effected following not any proxy
inquiry, but only if it is impossible to launch a file or cache
transfer inquiry in the current operating mode. Autodialling can be
done on an inquiry made by any of Eserv뭩 proxy servers. On modem
management see 6.5. (03.08.1999) | |
| FTP-gate is a proxy specific to the FTP
protocol. Unlike the HTTP & FTP proxy described in the previous
section, FTP-gate (sometimes called FTP-firewall) uses the FTP
protocol 뱋n both sides? i.e. for processing both the user program
and the enquired FTP Server. This allows to use such possibilities
of the FTP protocol, usually not used by browsers while working with
FTP, as reverse file transfer (server download) and secondary
(additional) file download for files whose transfer has been
interrupted.
Operating in FTP-gate, the proxy server itself becomes similar to
the FTP Server, with the only difference for the user program being
in the connection procedure. This is why most of the popular FTP
clients (CuteFTP, FAR, VoyagerFTP and many others) can work through
FTP-gate. Setup of these programs is described in a separate text
(see 6.4).
FTP-gate setup is done in the section ProxyServer/FTPproxy. This
proxy defaults to Port 3121.
Work of the FTPproxy is also affected by the general performance
setup of the Bind function (see 6.4.6). The Administrator can set
rules by which Eserv will select the network interface (and the IP
address) available on the server to work with the subnet possessing
the enquired server. Eserv defaults to identifying the interface,
and no manual bind setup is normally required. Nonetheless, in some
situations it can be useful (description see in 6.4.6).
(03.08.1999) | |
| The above proxy servers fulfil proxying of
most of the protocols used in the Internet, but there is a category
of client programs which will not work through proxy servers and
will only by direct Internet connection. In most cases such programs
can be 밺eceived?and forced to work through the proxy with the help
of the program SocksCapture and Eserv뭩 built-in Socks5-proxy. But
if the number of servers with which such an inapt program works is
negligible, or if SocksCapture for any reasons cannot intercept its
inquiries to the Internet, the below way of mapping external servers
into a local server can be useful.
TCPmapping and UDPmapping are setups for mapping local TCP and
UDP ports into ports of other servers. Mapping renders ports of the
local PC exact copies of the services operating on defined ports of
other computers in the Internet.
To add a TCP mapped link, click the icon picturing the sheet of
paper and correct the received template to achieve the required
mapping.
The template will look as:
TCPMAP: 3129 proxy.provider.com 3128
The first number here is the TCP port number on the local
computer (the service of the other computer will be mapped into this
port);
The second number is the IP address or the network name of the
computer whose service will be used;
The third number is the number of the port at which the mapped
service operates on the service computer.
To add a UDP mapped link, click the icon picturing the sheet of
paper and correct the received template to achieve the required
mapped link.
The template will look as:
UDPMAP: 53 194.87.234.6 53
The first number here is the UDP port number on the local
computer (the service of the other computer will be mapped into this
port);
The second number is the IP address or the network name of the
computer whose service will be used;
The third number is the number of the port at which the mapped
service operates on the service computer. (03.08.1999) | |
| DNS is a domain name service in the Internet,
a database containing information on conformity between IP addresses
and computer domain names, and some other data. Access to the DNS
database is effected through the DNS Server located by default at
UDP Port 53. The DNS Server accepts inquiries in UDP batches and
sends off response UDP batches.
User programs employ DNS facilities when receive the IP address
of a computer by its name (the IP address is needed to connect to
the server on the computer) and vice versa, the name by the IP
address. The programs normally do not use DNS directly, this is done
instead by their operating systems. However, if the operating system
cannot directly access the DNS Server, it will not be able to effect
such transformation. The exception is work with computer names in
the LAN, as for them Windows can effect such transformations without
DNS. Correspondingly, Windows-based LANs normally have no local DNS
Server, and LAN computers can work only with each other. As a rule
though, no DNS Server is required anyway: LAN computers work in the
Internet via proxy server, giving it the names of the Internet
computers, which the proxy is to contact. The proxy in turn performs
the transformation of the name into the IP address (the proxy server
works on a PC having direct access to the Internet and its DNS).
There is an exception to this rule: programs working through Socks4
or programs using Socks5 in the same way as Socks4 should obtain IP
addresses. This is a specific property of the Socks4 protocol - it
can process only inquiries containing the IP address of the target
computer rather than its name. Correspondingly, computers with
similar programs (e.g. the popular ICQ) should have access to DNS.
The simplest way to provide DNS access without installing a local
DNS Server is to use Eserv뭩 DNS proxy.
The DNS proxy is a special case of UDP mapping. Add in the
section ProxyServer/UDPDesplay the component
UDPMAP: 53 194.87.234.6 53
(Replace the IP address 194.87.234.6 with that of any real
available DNS Server, e.g. the IP address of the server of your
provider). Now save the configuration and reboot Eserv.
On doing this, a copy of the specified DNS Server will start on
the computer where Eserv is operating, sending to the Internet DNS
inquiries from computers in the LAN and forwarding back responses of
the real DNS Server. Of course, this works only if the PC carrying
Eserv (the Eserv PC) has an established Internet connection.
Mind that after installing the DNS proxy you should tell the
operating systems of the computers in the LAN the local IP address
of the Eserv PC as the address of the DNS Server, with the EXCEPTION
of the Eserv PC itself (this one still needs to be set up to the
provider뭩 DNS). The address of the DNS Server on the client
computers is set in the Windows dialogue ControlPanel/Network.
Select the line TCP/IP->network_card, click the Properties button
and select the bookmark DNS Configuration in the now displayed
dialogue. An example of setup of this element is shown in the figure
.img img\dns_proxy.gif img\dns_proxy_e.gif
In the field 밆NS Servers Browsing Sequence?enter the local IP
address of the PC carrying Eserv. In the field 밅omputer Name?enter
the name of the given client computer. In the field 밆omain?enter
the domain suffix (this line will be added to the Internet name of
the required computer if a reduced name is used and the DNS Server
cannot find the IP address of the computer by the short name). So,
if you write 뱈ydomain.com?in this field and then specify the
connection with the www computer in the program working on this
computer, Windows will try to find out the IP address of the local
www computer first; then, having failed to do so, will direct to the
DNS proxy an inquiry to obtain the address of the www computer;
then, in case of failure, to obtain the addresses
뱖ww.mydomain.com? 뱖ww. MYDOMAIN.COM? etc. (03.08.1999) | |
| Bind is described in the section
CommonSettings/ExtendedBind.
Setup of this section affects the work of the Socks proxy and FTP
proxy. They allow to set those IP addresses of your proxy server
that are assigned for connection by different network interfaces or
different external networks.
By default, the rules of automatic definition of these addresses
work (i.e. if nothing is specified in this section, Eserv/Eproxy
defines the addresses itself). Situations requiring intervention are
rare enough. A situation of this sort occurs in case of incorrect
ICQ operation (for more information read the file ICQ_over_Socks).
Another case occurs in a network closed for external access by
Firewall and NAT means. A third case is provided by operation of a
proxy server on multihomed PC뭩 (i.e. PC뭩 having several network
interfaces and IP addresses) in cases when there are more than two
network interfaces (three network cards, or two network cards and a
modem, etc., or several IP addresses on one interface).
To add the routing line in the directory SelectBind, enter in the
editing line below the following three values as:
subnet_IP_address subnet_mask interface_IP_address
where:
subnet_IP_address and subnet_mask are parameters of
the external network to which connection by the means of the proxy
server is done, for example 194.87.234.0 255.255.255.0,
interface_IP_address is the IP address of the proxy server PC to be
used for work with this network. Having input these three values,
click the Add button.
If dynamic assignment of IP addresses is used, it is possible to
specify the domain name as the third parameter instead of the IP
address. If prior to connection the domain name is not known either
(as in certain kinds of dialup connections), setup of this section,
being of no use, should be discarded. (03.08.1999) | |
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