Regular HTTP proxy – customer (itself) specify what is proxy server for him
Transparent proxy – customer does not know about the proxy being enabled and there isn’t need any additional configuration for web browser of client.
Access list by source, destination, URL and requested method (HTTP firewall)
Cache access list to specify which objects to cache, and which not.
Direct Access List – to specify which resources should be accessed directly, and which - through another proxy server
Logging facility – allows to get and to store information about proxy operation
Parent proxy support – allows to specify other proxy server, ('if they don’t have the requested object ask their parents, or to the original server.)
A proxy server usually is placed at various points between users and the destination server (also known as origin server) on the Internet. (see Figure 10.1).
A Web proxy (cache) watches requests coming from client, saving copies of the responses for itself. Then, if there is another request for the same URL, it can use the response that it has, instead of asking the origin server for it again. If proxy has not requested file, it downloads that from the original server.
There can be many potential purpose of proxy server:
- To decrease access speed to resources (it takes less time for the client to get the object).
- Works as HTTP firewall (deny access to undesirable web pages),
Allows to filter web content (by specific parameters, like source address, destination address and port, URL, HTTP request method) scan outbound content, e.g., for data leak protection.
Proxy configuration example
In MikroTik RouterOS proxy configuration is performed in /ip proxy menu. See below how to enable the proxy on port 8080 and set up 195.10.10.1 as proxy source address:
[admin@MikroTik] ip proxy> set enabled=yes port=8080 src-address=195.10.10.1
[admin@MikroTik] ip proxy> print
enabled: yes
src-address: 195.10.10.1
port: 8080
parent-proxy: 0.0.0.0:0
cache-drive: system
cache-administrator: "admin@mikrotik.com"
max-disk-cache-size: none
max-ram-cache-size: 100000KiB
cache-only-on-disk: yes
maximal-client-connections: 1000
maximal-server-connections: 1000
max-fresh-time: 3d
When setting up regular proxy service, make sure it serves only your clients and prevent unauthorised access to it by creating firewall that allow only your clients to use proxy, otherwise it may be used as an open proxy.
Transparent proxy configuration example
RouterOS can also act as a Transparent Caching server, with no configuration required in the customer’s web browser. Transparent proxy does not modify requested URL or response. RouterOS will take all HTTP requests and redirect them to the local proxy service. This process will be entirely transparent to the user (users may not know anything about proxy server that is located between them and original server), and the only difference to them will be the increased browsing speed.
To enable the transparent mode, firewall rule in destination NAT has to be added, specifying which connections (to which ports) should be transparently redirected to the proxy. Check proxy settings above and redirect us users (192.168.1.0/24) to proxy server.
[admin@MikroTik] ip firewall nat> add chain=dstnat protocol=tcp src-address=192.168.1.0/24 \
dst-port=80 action=redirect to-ports=8080
[admin@MikroTik] ip firewall nat> print
Flags: X - disabled, I - invalid, D - dynamic
0 chain=dstnat protocol=tcp dst-port=80 action=redirect to-ports=8000
[admin@MikroTik] ip firewall nat>
The web proxy can be used as transparent and normal web proxy at the same time. In transparent mode it is possible to use it as standard web proxy, too. However, in this case, proxy users may have trouble to reach web pages which are accessed transparently.
Proxy based firewall – Access List
Access list is implemented in the same way as MikroTik firewall rules processed from the top to the bottom. First matching rule specifies decision of what to do with this connection. Connections can be matched by its source address, destination address, destination port, sub-string of requested URL (Uniform Resource Locator) or request method. If none of these parameters is specified, every connection will match this rule.
If connection is matched by a rule, action property of this rule specifies whether connection will be allowed or not (deny). If connection does not match any rule, it will be allowed.
In this example assume that we have configured transparent proxy server as given in example above.
Block particular Websites.
/ip proxy access add dst-host=www.facebook.com action=deny
It will block website http://www.facebook.com, we can always block the same for different networks by giving src-address.
/ip proxy access add src-address=192.168.1.0/24 dst-host=www.facebook.com action=deny
Users from network 192.168.1.0/24 will not be able to access website www.facebook.com.
You can block also websites that contain specific words in URL:
/ip proxy access add dst-host=:mail action=deny
This statement will block all websites which contain word “mail” in URL. Like www.mail.com, www.hotmail.com, mail.yahoo.com etc.
We can also stop downloading specific types of files like .flv, .avi, .mp4, .mp3, .exe, .dat, …etc.
/ip proxy access
add path=*.flv action=deny
add path=*.avi action=deny
add path=*.mp4 action=deny
add path=*.mp3 action=deny
add path=*.zip action=deny
add path=*.rar action=deny.
Here are available also different wildcard characters, to creating specific conditions and to match it by proxy access list.
Wildcard properties (dst-host and dst-path) match a complete string (i.e., they will not match "example.com" if they are set to "example"). Available wildcards are '*' (match any number of any characters) and '?' (match any one character).
Regular expressions are also accepted here, but if the property should be treated as a regular expression, it should start with a colon (':').
To show that no symbols are allowed before the given pattern, we use ^ symbol at the beginning of the pattern.
To specify that no symbols are allowed after the given pattern, we use $ symbol at the end of the pattern.
Enabling RAM or Store based caching.
In this example it will presumed that you already have proxy configured and working and you just want to enable caching. If command/parameter detailed description is required check reference section which is located right below example section.
- RAM based caching:
- Good if you have device with considerable amount of RAM for caching. Enabling this on device with RAM 256MB or less will not give your network any benefit.
- Way faster cache write/read than one that is stored on usb or sata connected mediums.
- Store based caching:
- Larger proxy caches available simply due to medium capacity differences.
RAM proxy cache:
Important commands:
- max-cache-size=
- max-cache-object-size=
- cache-on-disk=
[admin@MikroTik] /ip proxy> set max-cache-size=unlimited max-cache-object-size=50000KiB cache-on-disk=no
...
[admin@MikroTik] /ip proxy> print
enabled: yes
src-address: ::
port: 8080
anonymous: no
parent-proxy: 0.0.0.0
parent-proxy-port: 0
cache-administrator: webmaster
max-cache-size: unlimited <-------
max-cache-object-size: 500000KiB <-------
cache-on-disk: no <-------
max-client-connections: 600
max-server-connections: 600
max-fresh-time: 3d
serialize-connections: no
always-from-cache: no
cache-hit-dscp: 4
cache-path: proxy-cache
Store proxy cache:
Important commands:
- max-cache-size=
- max-cache-object-size=
- cache-on-disk=
- cache-path=
[admin@MikroTik] > ip proxy set cache-on-disk=yes cache-path=/usb1/proxy/cache
[admin@MikroTik] > ip proxy print
enabled: yes
src-address: ::
port: 8080
anonymous: no
parent-proxy: 0.0.0.0
parent-proxy-port: 0
cache-administrator: webmaster
max-cache-size: unlimited <-------
max-cache-object-size: 50000KiB <-------
cache-on-disk: yes <-------
max-client-connections: 600
max-server-connections: 600
max-fresh-time: 3d
serialize-connections: no
always-from-cache: no
cache-hit-dscp: 4
cache-path: usb1/proxy/cache <-------
[admin@MikroTik] > file print
# NAME TYPE
0 skins directory
5 usb1/proxy directory
6 usb1/proxy/cache web-proxy store <-------
7 usb1/lost+found directory
Notes:
- This example shows how to configure caching for version starting from v6.20 as stores are now located in file menu as directories.
Check if cache is working:
[admin@MikroTik] > ip proxy monitor
status: running
uptime: 2w20h28m25s
client-connections: 15
server-connections: 7
requests: 79772
hits: 30513
cache-used: 481KiB
total-ram-used: 1207KiB
received-from-servers: 4042536KiB
sent-to-clients: 4399757KiB
hits-sent-to-clients: 176934KiB
Menu Specific commands
Access List
Access list is configured like a regular firewall rules. Rules are processed from the top to the bottom. First matching rule specifies decision of what to do with this connection. There is a total of 6 classifiers that specify matching constraints. If none of these classifiers is specified, the particular rule will match every connection.
If connection is matched by a rule, action property of this rule specifies whether connection will be allowed or not. If the particular connection does not match any rule, it will be allowed.
Wildcard properties (dst-host and dst-path) match a complete string (i.e., they will not match "example.com" if they are set to "example"). Available wildcards are '*' (match any number of any characters) and '?' (match any one character). Regular expressions are also accepted here, but if the property should be treated as a regular expression, it should start with a colon (':').
Small hints in using regular expressions:
- \\ symbol sequence is used to enter \ character in console
- \. pattern means . only (in regular expressions single dot in pattern means any symbol)
- to show that no symbols are allowed before the given pattern, we use ^ symbol at the beginning of the pattern
- to specify that no symbols are allowed after the given pattern, we use $ symbol at the end of the pattern
- to enter [ or ] symbols, you should escape them with backslash \.
- It is strongly recommended to deny all IP addresses except those behind the router as the proxy still may be used to access your internal-use-only (intranet) web servers. Also, consult examples in Firewall Manual on how to protect your router.
Direct Access
If parent-proxy property is specified, it is possible to tell proxy server whether to try to pass the request to the parent proxy or to resolve it connecting to the requested server directly. Direct Access List is managed just like Proxy Access List described in the previous chapter except the action argument.
Unlike the access list, the direct proxy access list has default action equal to deny. It takes place when no rules are specified or a particular request did not match any rule.
HTTP Methods
Options
This method is a request of information about the communication options available on the chain between the client and the server identified by the Request-URI. The method allows the client to determine the options and (or) the requirements associated with a resource without initiating any resource retrieval
GET
This method retrieves whatever information identified by the Request-URI. If the Request-URI refers to a data processing process than the response to the GET method should contain data produced by the process, not the source code of the process procedure(-s), unless the source is the result of the process.
The GET method can become a conditional GET if the request message includes an If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match, or If-Range header field. The conditional GET method is used to reduce the network traffic specifying that the transfer of the entity should occur only under circumstances described by conditional header field(-s).
The GET method can become a partial GET if the request message includes a Range header field. The partial GET method intends to reduce unnecessary network usage by requesting only parts of entities without transferring data already held by client.
The response to a GET request is cacheable if and only if it meets the requirements for HTTP caching.
HEAD
This method shares all features of GET method except that the server must not return a message-body in the response. This retrieves the metainformation of the entity implied by the request which leads to a wide usage of it for testing hypertext links for validity, accessibility, and recent modification.
The response to a HEAD request may be cacheable in the way that the information contained in the response may be used to update previously cached entity identified by that Request-URI.
POST
This method requests that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI.
The actual action performed by the POST method is determined by the origin server and usually is Request-URI dependent.
Responses to POST method are not cacheable, unless the response includes appropriate Cache-Control or Expires header fields.
PUT
This method requests that the enclosed entity be stored under the supplied Request-URI. If another entity exists under specified Request-URI, the enclosed entity should be considered as updated (newer) version of that residing on the origin server. If the Request-URI is not pointing to an existing resource, the origin server should create a resource with that URI.
If the request passes through a cache and the Request-URI identifies one or more currently cached entities, those entries should be treated as stale. Responses to this method are not cacheable.
TRACE
This method invokes a remote, application-layer loop-back of the request message. The final recipient of the request should reflect the message received back to the client as the entity-body of a 200 (OK) response. The final recipient is either the origin server or the first proxy or gateway to receive a Max-Forwards value of 0 in the request. A TRACE request must not include an entity.
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