What are Classes?
proftpd, it is sometimes nice, or even necessary,
to tag or label a client as belonging to some group, based on that client's
IP address or DNS hostname. A "class" is the name for such
connection-based groupings in ProFTPD terms. A class is defined to have
a name, and as having certain criteria such as IP addresses, IP
subnets/masks, and DNS hostnames. A client that connects to the daemon
that has matching characteristics is then labeled as belonging to that class.
Note that a connecting client can belong to only one class;
see the description below for how the winning class is selected for a session
from among multiple possible matches.
How are Classes Defined?
To define a class, use a
<Class> section in your
<Class internal> From 192.168.0.0/16 </Class>This defines a class named "internal"; any client connecting from 192.168.0.0/16 will belong to this class. And if you wanted to define a class for all clients not connecting from 192.168.0.0/16 address space:
<Class external> From !192.168.0.0/16 </Class>A more complicated class might include matching DNS names as well:
<Class test> From 220.127.116.11 From proxy.*.com From my.example.com From 18.104.22.168 </Class>This "test" class will then be used for a client with any of the defined characteristics.
Note that if your class rules use only DNS names, and
is unable to resolve the IP address of a client to a DNS name, that
class may not be matched as you might expect. This can be seen in
the server debugging output, at level 10, as something like:
comparing DNS name '22.214.171.124' to pattern 'proxy.*.com'Here you see the 126.96.36.199 IP address, where a DNS name should be. In order for DNS name based class rules to function properly, both a) DNS resolution is needed (i.e.
UseReverseDNS must be on, which
is the default), and b) the IP address of a connecting client must be
resolvable to a DNS name.
What if there are multiple classes defined, and the classes overlap, e.g. two classes both have:
From *.example.comWhich one will be used for the connecting client? This will depend on the order in which classes are defined in the
When searching the list of classes for the one that matches the client,
proftpd checks each class in the order in which they are defined.
The first class definition (in order of appearance in
proftpd.conf) that matches is used.
How do you define a class that includes all clients from a certain
domain except one specific host in that domain? To define a class with
these sorts of characteristics, use the
<Class foo> From *.example.com From !bad.example.com Satisfy all </Class>
Satisfy directive, when used within a
<Class> section, indicates whether any of the
From rules in the section need to match, or whether all of
From rules in the section need to match. The default
Satisfy setting for a
<Class> section is
To illustrate, the following class definition will never match:
<Class impossible> From 127.0.0.1 From !127.0.0.1 Satisfy all </Class>It is impossible to both an address and not match that same address, but that is what is demanded by the "Satisfy all" setting in the above class definition.
Now, where the use of "Satisfy all" comes in handy is when you have a general rule with exceptions:
<Class customers> From .domain.com From !host1.domain.com !host2.domain.com Satisfy all </Class>Specifically, the use of "Satisfy all" is necessary when you have multiple not matches (i.e. using the
! prefix), all
of which need to be evaluated.
How are Classes Used?
By itself, a class does nothing. It is merely a way to define a set of clients and to give that set a name. Once that name is defined, though, it can be use as part of your configuration. There are a limited number of configuration directives that make use of classes directly:
DenyClass directives are the
main directives to use, for example in
<Limit ALL> AllowClass internal DenyAll </Limit>
module also makes use of classes with its
configuration section. Using classes and
mod_ifsession, you can
proftpd.conf that has specific configurations for specific
classes of clients. Here's an example snippet demonstrating use of
<IfClass internal> MaxClients 100 </IfClass> <IfClass !internal> MaxClients 25 </IfClass>This allows clients from class "internal" to see an effective
MaxClients limit of 100 simultaneous clients, and clients
not in class "internal" to see an effective limit of only 25.