•
4.15.5 Specifying the Telnet or Local proxy command
4.15.1 Setting the proxy type
The ‘Proxy type’ radio buttons allow you to configure what type of proxy you want PuTTY to use for its network connections. The default setting is ‘None’; in this mode no proxy is used for any connection.
•Selecting ‘HTTP’ allows you to proxy your connections through a web server supporting the HTTP CONNECT command, as documented in
RFC 2817
.
•Selecting ‘SOCKS 4’ or ‘SOCKS 5’ allows you to proxy your connections through a SOCKS server.
•Many firewalls implement a less formal type of proxy in which a user can make a Telnet connection directly to the firewall machine and enter a command such as connect myhost.com 22 to connect through to an external host. Selecting ‘Telnet’ allows you to tell PuTTY to use this type of proxy.
•Selecting ‘Local’ allows you to specify an arbitrary command on the local machine to act as a proxy. When the session is started, instead of creating a TCP connection, PuTTY runs the command (specified in
section 4.15.5
), and uses its standard
input and output streams.
This could be used, for instance, to talk to some kind of network proxy that PuTTY does not natively support; or you could tunnel a connection over something other than TCP/IP entirely.
If you want your local proxy command to make a secondary SSH connection to a proxy host and then tunnel the primary connection over that, you might well want the -nc command-line option in Plink. See
section 3.8.3.14
for more information.
4.15.2 Excluding parts of the network from proxying
Typically you will only need to use a proxy to connect to non-local parts of your network; for example, your proxy might be required for connections outside your company's internal network. In the ‘Exclude Hosts/IPs’ box you can enter ranges of IP addresses, or ranges of DNS names, for which PuTTY will avoid using the proxy and make a direct connection instead.
The ‘Exclude Hosts/IPs’ box may contain more than one exclusion range, separated by commas. Each range can be an IP address or a DNS name, with a * character allowing wildcards. For example:
*.example.com
This excludes any host with a name ending in .example.com from proxying.
192.168.88.*
This excludes any host with an IP address starting with 192.168.88 from proxying.
192.168.88.*,*.example.com
This excludes both of the above ranges at once.
Connections to the local host (the host name localhost, and any loopback IP address) are never proxied, even if the proxy exclude list does not explicitly contain them. It is very unlikely that this behaviour would ever cause problems, but if it does you can change it by enabling ‘Consider proxying local host connections’.
Note that if you are doing DNS at the proxy (see
section 4.15.3
), you should make sure that your proxy exclusion settings do not
depend on knowing the IP address of a host. If the name is passed on to the proxy without PuTTY looking it up, it will never know the IP address and cannot check it against your list.
4.15.3 Name resolution when using a proxy
If you are using a proxy to access a private network, it can make a difference whether DNS name resolution is performed by PuTTY itself (on the client machine) or performed by the proxy.
The ‘Do DNS name lookup at proxy end’ configuration option allows you to control this. If you set it to ‘No’, PuTTY will always do its own DNS, and will always pass an IP address to the proxy. If you set it to ‘Yes’, PuTTY will always pass host names straight to the proxy without trying to look them up first.