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diff --git a/doc/configuration/simultaneous_use b/doc/configuration/simultaneous_use new file mode 100644 index 0000000..5639738 --- /dev/null +++ b/doc/configuration/simultaneous_use @@ -0,0 +1,173 @@ + + FreeRADIUS server and the Simultaneous-Use parameter. + + +0. INTRODUCTION + + Lots of people want to limit the number of times one user account can + login, usually to one. This is hard to do with the radius protocol; + the nature of the accounting stuff is such that the idea the radius server + has about the list of logged-in users might be different from the idea + the terminal server has about it. + + However, most terminal servers have an alternative way to get a list + of logged-in users. Most support some way through telnet, some have + a finger-daemon builtin and a lot of them support SNMP. So if the + radius server thinks that someone is trying to login a second time, + it is possible to check on the terminal server itself if the first + login is indeed still active. Only then access is denied for the + second login. + + +1. PREREQUISITES + + You need to have perl installed. + + For SNMP checks, you have 2 options. You can use the `snmpget' program + from the cmu-snmp tools. You can probably get precompiled ones, + maybe even packaged for your system (Debian/Linux, Redhat/Linux, FreeBSD + ports collection etc). The source code is at + http://www.net.cmu.edu/projects/snmp/snmpapps/. The Linux-specific + version of this is at http://www.gaertner.de/snmp/ + + The other option is to install the SNMP_Session and BER modules that + for example the well known `mrtg' package uses. This is recommended. + In that case you need no external snmpget program, checkrad will + speak SNMP directly. See http://www.switch.ch/misc/leinen/snmp/perl/ + + The checkroutine for USR/3Com Total Control racks uses the Net::Telnet + module from CPAN, at least version 3.00. If you need that, obtain it from + your local CPAN mirror (or see http://www.perl.com/CPAN/). The checkrad.pl + perl script will autodetect if that module is installed. + +2. USAGE. + + It works by adding the `check' parameter "Simultaneous-Use" to the entry + for a users or DEFAULT in /etc/raddb/users. It should be at least one; + it defines the maximum number of users logged in with the same account name. + For example: + + # + # Simultaneous use restrictions. + # + DEFAULT Group == "staff", Simultaneous-Use := 4 + Fall-Through = 1 + DEFAULT Group == "business", Simultaneous-Use := 2 + Fall-Through = 1 + DEFAULT Simultaneous-Use := 1 + Fall-Through = 1 + + + NOTE!!! The "Simultaneous-Use" parameter is in the "check" A/V pairs, + and not in the Reply A/V pairs (it _is_ a check). + + For SQL, after creating and populating your schema, you should + execute the following statement (for MySQL, others may vary): + + INSERT INTO radgroupcheck (GroupName, Attribute, op, Value) values("dialup", "Simultaneous-Use", ":=", "1"); + + Once that is done, your users should be limited to only one login at a time. + +3. IMPLEMENTATION + + The server keeps a list of logged-in users in the /var/log/radutmp file. + This is also called "the session database". When you execute "radwho", + all that radwho really does is list the entries in this file in a pretty + format. Only when someone tries to login who _already_ has an active + session according to the radutmp file, the server executes the perl + script /usr/local/sbin/checkrad (or /usr/sbin/checkrad, it checks for + the presence of both and in that order). This script queries the terminal + server to see if the user indeed already has an active session. + + The script uses SNMP for Livingston Portmasters and Ciscos, finger for + Portslave, Computone and Ascend, and Net::Telnet for USR/3Com TC. + + Since the script has been witten in perl, it's easy to adjust for + any type of terminal server. There are implementations in the script for + checks using SNMP, finger, and telnet, so it should be easy to add + your own check routine if your terminal server is not supported yet. + + You can find the script in the file src/checkrad.pl. + + You need to set the correct type in the file /etc/raddb/naslist so that + checkrad KNOWS how it should interrogate the terminal server. At this + time you can define the following types: + + type Vendor Uses method needs Need naspasswd + ==== ====== =========== ===== ============== + ascend Lucent SNMP SNMP No + bay Nortel finger finger command No + cisco Cisco SNMP SNMP Optional [1] + computone Computone finger finger command No + cvx Nortel SNMP SNMP No + digitro Digitro rusers rusers command No + livingston Livingston SNMP SNMP No [2] + max40xx Lucent finger finger command No + netserver USR/3com telnet CPAN Net::Telnet Yes + pathras Cyclades telnet CPAN Net::Telnet Yes + patton Patton SNMP SNMP No + portslave ? finger finger command No + pr3000 Cyclades SNMP snmpwalk command No + pr4000 Cyclades SNMP snmpwalk command No + tc USR/3com telnet CPAN Net::Telnet Yes + usrhyper USR/3com SNMP SNMP No [3] + versanet VersaNet SNMP SNMP No + + other none N/A - No + + [1] In naspasswd file: set username to SNMP, password is community. + [2] Needs at least ComOS 3.5, SNMP enabled. + [3] Set "Reported Port Density" to 256 (default) + + "other" means "don't bother checking, I believe what radutmp says". + This really is not recommended, if a user has a "stuck" entry in the + session database she will not be able to login again - hence the + extra check that "checkrad" does. + +4. IF IT DOESN'T WORK + + Note that you need to add the Simultaneous-Use parameter to the + check item (first line), not the reply item, using the ':=' operator. + + You can edit the `checkrad' perl script and turn on debugging. Then + watch the debug file. The `radius.log' file also gives some hints. + + You can also run the "checkrad" script manually, use the "-d" + switch to get debug output on standard output instead of in the log. + + See also: + + http://wrath.geoweb.ge/simult.html + + which has a good discussion of the use of Simultaneous-Use. + + +5. CAVEATS + + This solution checks the radutmp file. This file is kept up-to-date from + the Accounting records the NAS sends. Since some NASes delay these records + for quite some time, it is possible to get a double login by logging in + twice at _exactly_ the same time (plus or minus the mentioned delay time), + since neither of the logins are registered yet. + + The solution would be to create a small 1-minute cache of Authentication + records, that is also checked for double login attempts. Perhaps in the + next version. + + When implementing this one thing was considered the most important: when + trying to detect double logins, we always try to err on the safe side. So + in rare cases, a double login is possible but we try never to limit access + for a legitimate login. + +6. PROBLEMS WITH DROPPED CONNECTIONS + + Our PM3, with 2 ISDN-30 lines coming into it, had the habit of sometimes + dropping connections. In a few cases, the portmaster thought the session was + still alive so if the user tried to login again, he or she was denied access. + In our case, this problem was caused by a bad PRI line from the phone + company. + + We tried to compensate this by setting the Idle-Timeout to 15 minutes. That + way, even if a user did get locked out the portmaster would clear the rogue + session within 15 minutes and the user could login again. + |