Squid - ACLs - ACL Types

Access control settings are among the most important features of Squid. You can configure Squid to set filters for various entities and at different granularities (e.g. filters for specific protocols, filters for certain types of commands, filters for specific routers, filters for specified domains, etc).

acl	src	dst	myip	arp
srcdomain	dstdomain	srcdom_regex	dstdom_regex	time
url_regex	urlpath_regex	urllogin	port	myport
proto	method	browser	referer_regex	ident
ident_regex	src_as	dst_as	proxy_auth	proxy_auth_regex
snmp_community	maxconn	max_user_ip	req_mime_type	req_header
rep_mime_type	rep_header	external	urlgroup	user_cert
ca_cert	ext_user	ext_user_regex
follow_x_forwarded_for	acl_uses_indirect_client	delay_pool_uses_indirect_client	log_uses_indirect_client	http_access
http_access2	http_reply_access	icp_access	htcp_access	htcp_clr_access
miss_access	cache_peer_access	ident_lookup_access	tcp_outgoing_tos	tcp_outgoing_address
reply_header_max_size	reply_body_max_size	log_access

Example

Recommended minimum acl configuration

Recommended minimum http_access configuration

acl

Used to define an Access List.

acl aclname acltype string1 ...
acl aclname acltype "file"

where

aclname: Name of the acl. Can be anything.
acltype: Type of acl. The possible types include the requesting clients address, the Web server address or host name, a regular expression matching the URL, and many more.
string: String to match. This may be an IP address, a series of IP addresses, a URL, a host name, etc.
file: File that containing strings. The file should contain one item per line.

src

Matching done based on clients IP address.

The IP address of the requesting client, or the clients IP Address.

acl aclname src ip-address/netmask ... (clients IP address)
acl aclname src addr1-addr2/netmask ... (range of addresses)

where:

aclname: Access list name.
ip-address: Clients IP address.
netmask: Network mask.
add1-addr2: Range of ip address.

Examples:

acl network1 src 172.16.1.0/24 - refers to the whole Network with address 172.16.1.0
acl source1 src 172.16.1.25/32 - refers to a single source
acl srcrange src 172.16.1.25-172.16.1.35/32 - refers range of IP Addresses from 172.16.1.25-172.16.1.35

dst

Same as src but looks for destination IP Address.

First Squid will dns-lookup for IPAddress from the domain-name, which is in request header. Then this acl is interpreted.

acl aclname dst ip-address/netmask ... (URL host's IP address)

where:

aclname: Access list name.
ip-address: ip-address of the oirgin server/machine.
netmask: Network mask.

Examples

acl dest dst 63.194.81.67/32

myip

The local IP address on which the client connection exists.

This allows ACLs to be constructed that only match one physical network, if multiple interfaces are present on the proxy, among other things.

acl aclname myip ip-address/netmask ... (local socket IP address)

where:

aclname: Access list name.
ip-address: IP address of the local machine.
netmask: Network mask.

Example:

acl myip1 myip 172.16.1.53/32

arp

Ethernet (MAC) address matching.

Build Option:

-enable-arp-acl

This option only works for clients on the same local subnet, and only for certain platforms:

Linux
Solaris
Some BSD variants

This ACL can provide a somewhat secure method of access control, because MAC addresses are usually harder to spoof than IP addresses, and you can guarantee that your clients are on the local network (otherwise no ARP resolution can take place).

acl aclname arp mac-address

where:

aclname: Access list name.
mac-address: Physical address to be matched.

Example(s)

acl ACLARP arp 11:12:13:14:15:16

ACLARP refers to the MACADDRESS of the ethernet 11:12:13:14:15:16.

NOTE: Squid can only determine the MAC address for clients that are on the same subnet.

If the client is on a different subnet, then Squid cannot find out its MAC address.

srcdomain

Matches against the client domain name.

Matching can be either a single domain name, or a list or domain names, or the path to a file that contains a list of domain names.

NOTE: If a path to a file, it must be surrounded by parentheses.

This ACL type can increase the latency, and decrease throughput significantly on a loaded cache, as it must perform an address-to-name lookup for each request, so it is usually preferable to use the Client IP Address type.

aclname srcdomain .domain-name ...

NOTE: Here “.” is more important.

where

aclname: Access list name.
domain-name: Clients domain name.

Example:

acl mydomain srcdomain .sharewiz.net

dstdomain

This refers to destination domain.

acl aclname dstdomain .domain-name ...

NOTE: Here “.” is more important.

where:

aclname: Access list name.
omain-name: Destination domain.

Example(s)

acl domain1 dstdomain .sharewiz.net

This looks for *.sharewiz.net from URL

srcdom_regex

Matches against the client domain name.

Matching can be either a single domain name, or a list of domain names, or a path to a file that contains a list of domain names.

NOTE: If a path to a file is specified, it must be surrounded by parentheses.

acl aclname srcdom_regex [-i] pattern ...

where:

aclname: Access list name.
pattern: Pattern to match.

Example:

acl aclname srcdom_regex sharewiz

This looks for the word sharewiz from the client domain name

dstdom_regex

Matching done on destination domain based on regular expression.

acl aclname dstdom_regex [-i] pattern ...

where:

aclname: Access list name.
pattern: Patern to match.

Example(s)

acl domain1 dstdom_regex redhat

This looks for the word redhat from the client's request.

time

Provides time filter settings; hat are active during certain times of the day or certain days of the week.

This feature is often used to block some types of content or some sections of the internet during business or class hours.

Many companies block pornography, entertainment, sports, and other clearly non-work related sites during business hours, but then unblock them after hours.

This might improve workplace efficiency in some situations (or it might just offend the employees).

This ACL type allows you to enter days of the week and a time range, or select all hours of the selected days.

acl aclname time [day-abbrevs] [h1:m1-h2:m2]

where:

aclname: Access list name.
day-abbrevs: Days list (as shown above).
h1:m1-h2:m2: From and To time

Day-abbrevs:

S	Sunday
M	Monday
T	Tuesday
W	Wednesday
H	Thursday
F	Friday
A	Saturday

Time:

h1:m1 must be less than h2:m2

Example:

acl acltime time M 9:00-17:00

acltime refers to day of Monday and time from 9:00 to 17:00.

url_regex

Matches using a regular expression on the complete URL.

Can be used to provide access control based on parts of the URL or a case insensitive match of the URL, and much more.

The regular expressions used in Squid are provided by the GNU Regex library which is documented in the section 7 and 3 regex manpages.

acl aclname url_regex [-i] pattern

where:

aclname: Access list name.
pattern: Matching to be done for.

Example:

acl reject url_regex -i ^https://www.google.co.uk/index.html

Reject contains the entire url https://www.google.co.uk/index.html.
- If in the http_access you deny reject, it will deny only the URL https://www.google.co.in/index.html but allows the URL https://www.google.co.uk.

urlpath_regex

Matches on the URL path minus any protocol, port, and host name information.

If the words are found it will match.

acl aclname urlpath_regex [-i] pattern

where:

aclname: Access list name.
pattern: Pattern which is expected for match.

Example:

acl reject url_regex -i index.html

reject: contains the pattern index.html.
- If in the http_access if you deny reject, then for any url containing the pattern index.html will be denied.

urllogin

Regular Expression matching on URL login field.

acl aclname urllogin [-i] [^a-zA-Z0-9] ...

where:

aclname: Access list name.
pattern: Pattern which ia expected for match.

Example:

acl urllogin -i adminstrator

port

Matching done on the destination port.

acl aclname port port-number
acl aclname port range

where:

aclname: Access list name.
port-number: Destination port number.
range: Range of port numbers.

Example:

acl acceleratedhost dst 172.16.1.115/255.255.255.255
acl acceleratedport port 80
acl mynet src 172.16.1.0/255.255.255.0
http_access allow acceleratedhost acceleratedport mynet
http_access deny all

The following allows access only to the destination 172.16.1.115:80 from network 172.16.1.0

myport

This provides match against local socket TCP interface port.

	
acl aclname myport port-numbers ...

where:

aclname: Access list name.
port-numbers: Local interface port numbers.

Example(s)

acl mp myport 3128
http_access deny 3128
http_access allow all

These will deny all requests coming to the port 3128.

Allows requests coming at all other ports.

proto

Matching done based on protocol used in the request such as FTP, HTTP, ICP, etc.

acl aclname proto protocol

where:

aclname: Access list name.
protocol: Protocol to be matched.

Example:

acl myproto proto HTTP FTP

This refers to HTTP and FTP protocols.

method

Matching done based on the HTTP request method like GET, PUT, etc.

acl aclname method method-type

where:

aclname: Access list name.
method-type: HTTP request method.

Example(s)

acl getmethod method GET POST

This refers to the GET and POST methods only.

browser

A regular expression that matches the clients browser type based on the user agent header

For example, using this ACL type, one could create an ACL for Netscape users and another for Internet Explorer users.

acl aclname browser [-i] regexp

where:

aclname: Access list name.
regexp: Browser name.

Example:

acl aclname browser MOZILLA

This refers to the requests, which are coming from the browsers who have “MOZILLA” keyword in the user-agent header.

referer_regex

Pattern match on Referer header.

WARNING: Referer is highly unreliable, so use with care.

acl aclname referer_regex [-i] pattern

where:

aclname: Access list name.
pattern: Pattern to be matched.

Example:

In your Squid.conf configuration file you would write something like this,

acl expression referer_regex -i user1

This looks for the pattern “user1” in username

ident

Provides string matching on user name.

Matching based on iden lookups.

NOTE: Need an external ident server server running on the client machines.

acl aclname ident username ...

where:

aclname: Access list name.
username: Username to be matched.

Example:

You can use ident to allow specific users access to your cache.

In your Squid.conf configuration file you would write something like this,

ident_lookup_access allow all
acl friends ident kim lisa frank joe
http_access allow friends
http_access deny all

ident_regex

Provides string match on ident output.

Same as ident but matching is done on ident output.

NOTE: Need an external ident server server running on the client machines.

acl aclname ident_regex [-i] pattern

where:

aclname: Access list name.
pattern: Pattern to be matched.

Example:

In your Squid.conf configuration file you would write something like this,

ident_lookup-access allow all
acl friends ident_regex joe

This looks for the pattern “joe” in username

src_as, dst_as

Source Autonomous System Number is another AS related ACL type, and matches on the AS number of thesource of the request,

Destination Autonomous System Number is the AS number of the server being queried.

~The autonomous system number ACL types are generally only used in Cache Peer, or ICP, access restrictions.

Autonomous system numbers are used in organizations that have multiple internet links and routers operating under a single administrative authority using the same gateway protocol.

Routing decisions are then based on knowledge of the AS in addition to other possible data.

acl aclname src_as number
acl aclname dst_as number

where:

aclname: Access list name.
number: AS numbers to be matched.

Example:

An example for routing all requests for AS#1241 and only those to mycache.mydomain.net

acl asexample dst_as 1241
cache_peer_access mycache.mydomain.net allow asexample
cache_peer_access mycache_mydomain.net deny all

proxy_auth

This ACL type calls an external authenticator process to decide whether the request will be allowed.

Some of the authenticator helper programs available for Squid are PAM, NCSA, UNIX passwd, SMB, NTLM, etc.

Note that authentication cannot work on a transparent proxy or HTTP accelerator. The HTTP protocol does not provide for two authentication stages (one local and one on remote Web sites).

So in order to use an authenticator, your proxy must operate as a traditional proxy, where a client will respond appropriately to a proxy authentication request as well as external Web server authentication requests.

NOTE: proxy_auth can't be used in a transparent proxy.

It collides with any authentication done by origin servers.

It may seem like it works at first, but it doesn't.

When a Proxy-Authentication header is sent but it is not needed during ACL checking the username is NOT logged in access.log.

acl aclname proxy_auth [-i] username ...

where:

aclname: Access list name.
username: User name to be authenticated.

Example:

<CODE> acl ACLAUTH proxy_auth peter john james http_access allow ACLAUTH http_access deny all </CODE>

The above configuration will allow only peter, john and james if they give valid username and password.

proxy_auth_regex

As above, this ACL calls an external authenticator process, but allows regex pattern or case insensitive matches.

Matching based on regular expressions using external authentication process.

acl aclname proxy_auth_regex [-i] pattern

where:

aclname: Access list name.
pattern: Pattern to be matched.

Example:

acl ACLAUTH proxy_auth_regex -i mesh

snmp_community string ...

matching against SNMP community stringS to limit access to your SNMP Agent.

acl aclname snmp_community string ...

where:

aclname: Access list name.
string: String to be matched.

Example:

acl snmppublic snmp_community public

maxconn

Matches when the client's IP address has more than the specified number of HTTP connections established.

acl aclname maxconn number

where:

aclname: Access list name.
number: Maximum number of HTTP connections.

Example:

acl someuser src 1.2.3.4
acl twoconn maxconn 5
http_access deny someuser twoconn
http_access allow !twoconn

The above configuration will allow a maximum of 5 http connection to access.

max_user_ip

This will be matched when the same user attempts to log in for more than the specified number of times from different addresses,

If -s is specified then the limit is strict, denying browsing from any further IP addresses until the ttl has expired.

Without -s Squid will just annoy the user by “randomly” denying requests. (the counter is then reset each time the limit is reached and a request is denied).

The authenticate_ip_ttl parameter controls the timeout on the IP entries.

NOTE:

1. Any authentication program must be running for this. NCSA will a simple configuration.

2. In acceleration mode or where there is mesh of child proxies, clients may appear to come from multiple addresses if they are going through proxy farms, so a limit of 1 may cause user problems.

acl aclname max_user_ip [-s] number

where:

aclname: Access list name.
number: Number of times to login.

Example:

authenticate_ip_ttl 2 hours
acl maxuser max_user_ip -s 2
http_access deny maxuser

The same user can log to a maximum of 2 times from two different machines and when he tries to login for the third time from a third system, he will not be allowed to browse.

req_mime_type

Match against the mime type of the request generated by the client.

Using this you can detect file upload or some types HTTP tunneling requests.

acl aclname req_mime_type mime_type ...

where:

aclname: Access list name.
mime_type: Mime type at the requesting side.

Example:

acl mymime req_mime_type text

This acl looks for the pattern “text” in request mime header.

NOTE: This does NOT match the reply.

You cannot use this to match the returned file type.

req_header

Regular Expression match against any of the known request headers.

May be thought of as a superset of “browser”, “referer” and “mime-type” ACLs.

acl aclname req_header header-name [-i] regular Expression

where:

aclname: Access list name.
header-name: Name at the requesting side.

Example:

acl myheader req_header text

This acl looks for the pattern “text” in request header.

rep_mime_type

Match against the mime type of the reply received by Squid.

Using this, you can detect file download or some types HTTP tunneling requests.

This has no effect in http_access rules. It only has effect in rules that affect the reply data stream such as http_reply_access.

acl aclname rep_mime_type mime_type ...

where:

aclname: Access list name.
mime_type: Mime type at the receiving side.

Example:

acl m2 rep_mime_type ^application/pdf$
http_reply_access deny m2

This blocks access to application/pdf mime types.

rep_header

Regular Expression match against any of the known response headers.

acl aclname rep_header header-name [-i] regular expression...

where:

aclname: Access list name.
header-name: Header name at the receiving side.

Example:

acl many_spaces rep_header Content-Disposition -i [[:space:]]3,

external

Provides match against external ACL lookup via a helper class defined by the external_acl_type tag.

acl aclname external class_name [arguments...]

where:

aclname: Access list name.
class_name: Defined by external_acl_type tag.

Example:

auth_param basic program < put your authenticator here >
auth_param basic children 20
auth_param basic realm Squid proxy-caching web s

Wiki

Table of Contents

Squid - ACLs - ACL Types

acl

src

dst

myip

arp

srcdomain

dstdomain

srcdom_regex

dstdom_regex

time

url_regex

urlpath_regex

urllogin

port

myport

proto

method

browser

referer_regex

ident

ident_regex

src_as, dst_as

proxy_auth

proxy_auth_regex

snmp_community string ...

maxconn

max_user_ip

req_mime_type

req_header

rep_mime_type

rep_header

external