nethserver-squid

This package configure the well-known Squid web proxy.

Squid rpms are from upstream.

Configuration

All properties are saved in the squid key under the configuration database.

Properties:

  • BlueMode: change Squid operation mode on blue networks. It has same values and defaults of GreenMode
  • BypassDomains: comma separeted list of domains bypassed when the proxy is set in transparent mode
  • DiskCache: disabled by default, if enabled it actives the disk caching system for squid
  • DiskCacheSize: maximum value of squid cache on disk
  • GreenMode: change Squid operation mode on green networks. Can be: manual, authenticated, transparent, transparent_ssl. Default is: manual
  • KrbPrimaryList: name for Kerberos keytab (used for Active Directory integration)
  • KrbStatus: if set to enabled a ticket credential cache file is kept valid by the hourly cron job (used for Active Directory integration)
  • MaxObjSize: objects larger than this setting will not be saved on disk. If speed is more desirable than saving bandwidth, this should be set to a low value
  • MemCacheSize: value of squid cache on memory
  • MinObjSize: can be left at 0 to cache everything, but may be raised if small objects are not desired in the cache.
  • NoCache: comma separated list of domains which will be not cached
  • ParentProxy: in the form host:port, if omitted port is default to 3128. Default is empty
  • PortBlock: if enabled, block port 80 and 443. Default is: disabled
  • SafePorts: comma separated list of ports thath can be accessed through the proxy. Listed ports will be added to the default list of safe and ssl ports

Database example

Example:

squid=service
   BlueMode=manual
   DiskCache=disabled
   DiskCacheSize=100
   GreenMode=transparent
   KrbPrimaryList=HTTP
   KrbStatus=enabled
   MaxObjSize=4096
   MemCacheSize=256
   MinObjSize=1
   NoCache=www.nethserver.org
   ParentProxy=
   PortBlock=disabled
   TCPPorts=3128,3129,3130
   access=private
   status=enabled

Transparent mode

When the proxy is enabled in transparent mode, all traffic destined to the port 80 is redirect to the Squid (port 3129). This configuration requires Shorewall.

SSL peek and splice

If the proxy is enabled in transparent SSL mode, also all traffic destined to port 443 is redirected to Squid (port 3130). The daemon does not inspect SSL traffic, but visited sites can be processed using the web filter.

Known bugs

You could find this kind of errors inside /var/log/squid/cache.log

2016/12/09 09:44:18 kid1| SECURITY ALERT: on URL: avatars0.githubusercontent.com:443
2016/12/09 09:44:18 kid1| SECURITY ALERT: Host header forgery detected on local=151.101.60.133:443 remote=192.168.5.22:40950 FD 166 flags=33 (local IP does not match any domain IP)

In this case, when accessing github, the avatars won’t be displayed by the browser, and you can find a “Timeout error” for the not loaded images.

This kind of errors can’t be fixed. See official documentation for workarounds:

Authenticated mode

Authentication schema depends on system configuration:

  • standard authentication for system users is done over LDAP
  • if Samba AD is installed, clients can use Kerberos (SPNEGO/GSSAPI)

Bypasses

The implementation supports 3 kind of bypass:

  • source bypass
  • destination bypass
  • domains bypass

Source and destination bypass

Bypass rules are saved inside the fwrules databases. A bypass can be of two types:

  • bypass-src: listed origin host are bypassed
  • bypass-dst: listed target host are bypassed

Properties: * Host: a host object, like a remote or local host * status: can be enabled or disabled * Description: optional description

Bypass example:

boss=bypass-src
   Description=Boss without proxy
   Host=host;bosspc
   status=enabled

Domains bypass

All requests to domains listed inside the BypassDomains property will not be redirect to the transparent proxy.

The implementation uses the ipset feature of Dnsmasq. Each time a listed domain is accessed from the client, Dnsmasq resolves the IP and add it to squid-bypass ipset. The squid-bypass ipset is then used as exception inside Shorewall REDIRECT rule.

Notes:

  • all clients must use the server as DNS
  • Dnsmasq name resolution works for the listed domains and all sub-domains

Cache

There is an event called nethserver-squid-clear-cache that empties the cache.

Priority and divert rules

The squid database contains multiple records of type rule.

Each rule has following properties:

  • key: it’s a numeric uniq id
  • Action:
    • priority;low: add low priority packet marker using tcp_outgoing_mark
    • priority;high: add high priority packet marker using tcp_outgoing_mark
    • provider;<name>: add packet marker for provider <name> using tcp_outgoing_mark
    • force;<name>: force output traffic to <name> provider using tcp_outgoing_address
  • Description: optional description
  • Dst: comma-separeted list of domains, this is converted to a dstdomain ACL
  • Src: firewall object, supported objects are: role, host, zone, ip range and cidr . This is converted to src ACL
  • status: can be enabled or disabled

Example:

1=rule
   Action=priority;low
   Description=
   Dst=yahoo.com
   Src=host;giacomo
   status=enabled
2=rule
   Action=provider;fast
   Description=
   Dst=nethserver.org,nethesis.it
   Src=host;birro
   status=enabled
3=rule
   Action=force;slow
   Description=
   Dst=
   Src=cidr;cidr1
   status=enabled

WPAD

WPAD is located at /var/www/html/wpad.dat. The web server is configured to allow the download only from trusted and blue networks, but be aware that you need to manually open the httpd port for blue networks (see Add a new service).

The WPAD returns:

  • DIRECT, if squid is disabled or the requesting client is inside a network where the proxy is configured in transparent mode
  • IP of corresponding network interface, if the requesting client is inside a network where the proxy is configured in manual or authenticated mode
  • proxy.<domain>, if the server is joined to Active Directory and the requesting client is inside a network where the proxy is configured in manual or authenticated mode

Also WPAD file includes all source and destination bypasses.

Miscellaneous options

The following options are always enabled:

  • buffered logs
  • SNMP support on port 3401