It then starts an instance of the requested service and passes control of the connection to it. Once the connection is established, xinetd does not interfere further with communication between the client host and the server. As with xinetd. Each has a series of constants that you need to feed into the option as parameters.
Possible values are:. For example:. Two more options that you need to put into xinetd. This is an important factor and it is a simple, but powerful way to trounce Denial of Service DoS attacks. Unfortunately, the implementation of this service limit will block out genuine users for the duration of the attack.
Putting together all of the details explained in this section, your xinetd. Each xinetd. For each of the services that you want your server to deliver, you should write a service instruction section in xinetd.
You can also overwrite the settings defined in the defaults sections by restating those attributes with different values in the section written to define a service. The attributes available for the services section is different for each of three categories of service. These are:. However, this attribute is not mandatory and is often left out. When writing an attribute specification, all fields are separated by spaces or carriage returns — you do not use any form of separator or punctuation in the definition.
Used when calling tcpd. Using these attributes again will overwrite any values set for them in the defaults section. The two time ranges are separated by a space. The time definitions use the hour clock format. The services definition uses the service name as its identifier by default. However, you might want to create several copies of a service and give each different attributes.
However, the id attribute enables this operating strategy. One very common usage of this scenario would be when you want to create different FTP servers for internal and external access. By this method, you can keep your file storage for the office completely separate from the downloadable files that you make available to the general public. From then on, xinetd can distinguish between the two. The scenario of creating different services for internal and external users can be greatly helped by the bind attribute.
It usually means to associate a connection to a port, thus creating an id for the session. However, it is safer to leave those restrictions in. So, the full definition of your internal and external FTP servers would be:. This strategy requires that your FTP server has a static IP address allocated to it for public access.
Although the above scenario works when a single computer is used for both internal and external access, you can also allocate the addresses of separate computers for each FTP instance. These services are a security weakness because they can be used by hackers to gain information about your network and server. Therefore, it is better to disable them.
You can do this with the disabled attribute, which goes into your defaults definition. Just include the following line in your defaults section to remove these facilities:. You start xinetd at the command line. The program can be run with the following options:. If you have a Linux computer, you might have xinetd installed already. You can check by running xinetd -version. Currently, its biggest drawback is RPC support instability, but you can start protmap , and it xinetd coexistence to solve this problem.
In principle, any system service can use xinetd , however, it should be those best suited to commonly used network services, at the same time, the number of requests and the frequency of service is not too high. Like DNS and Apache is not suitable for use in this way, and like FTP , Telnet , SSH and the like suitable for use on xinetd mode, the system defaults to xinetd services can be divided into the following categories.
Excerpts from this document is as follows:. Internet network services file, record the network service name and port number and the corresponding protocols they use. Each line in the file corresponds to a service that a 4 fields composed of, in the middle Tab separated spacebar key or, respectively, " service name " , " using port " , " protocol name " and " alias ".
In general, do not modify the content of the file, because these settings are Internet standards setting. Once modified, the system may cause conflict, so that users can not access resources properly. For example, disable attribute is set to yes , indicate the service is disabled; disable attribute is set to no , indicate the service is enabled. Simpleconfiguration file for xinetd. The following describes the meaning of each line options. Wherein the service is a required keyword, and the attribute table must be enclosed in braces.
Each of which is defined by the service-name defined services. There are many attributes that can be used, the use of rules required attributes and attributes will be described later.
0コメント