The ALIAS keyword

The purpose of the ALIAS keyword is to allow for easier transition from earlier versions of FreeRADIUS to version 4. We recognize that the old attribute names are used in many places such as databases. It can be difficult to change many thousands of existing entries in a "live" system.

As such, we provide some ability to use names which are compatible with version 3 of FreeRADIUS.

All of the attributes have been renamed from v3. This change was necessary in order to support new functionality in v4. The unfortunate side effect of this change is that all of the names which are currently in SQL, LDAP, and the "files" module for use with v3, are incompatible with v4.

We recognize that is is difficult to change every entry in a database, especially when there’s no clear mapping between the "old" and "new" names. This renaming is made more complex because the "new" names need to be grouped and arranged in ways that the old ones were not.

The "old" names were all in flat lists, so that User-Name appeared next to Cisco-AVPAir. This organization was simple enough to work for 20 years, but its time has come. The new names are hierarchical, and are contained in "parent" attributes. This arrangement does not ysyakky change the length of most attribute names.

For v4, the Cisco-AVPair attribute is called AVPair, and it lives inside of the Cisco namespace, which in turn lives inside of the Vendor-Specific namespace. So the new name for Cisco-AVPair is Vendor-Specific.Cisco.AVPair.

This process continues for many thousands of vendor-specific attributes.

Happily, it is possible to (mostly) use the old names with v4. There are limitations, but it will mostly work. The main reason for enabling the old names is to try out v4 with a database that is also used by v3. This lets you test that v4 works, without going through a complex "upgrade everything" process.

The old v3 names are in "alias" dictionaries, in the ${dictdir} directory. To find out where this directory is on your local system, run radiusd -h or radclient -h. Then look for the -D command-line option, and it will tell you where the dictionary files are located.

The v3 names are in ${dictdir}/radius/alias/VENDOR.txt where VENDOR is the (lowercase) name of the vendor, which is taken from the VENDOR definition in the v3 dictionaries.

You will need to add a $INCLUDE line for each vendor-specific dictionary which is used by your local system. The default v4 dictionaries do not enable all of v3 compatibility names.

Yes, we recognize that this process is a bit of work. However, we wish to encourage everyone using v4 to upgrade to using the new v4 features. Our experience shows that if we automatically enable "compatibility functions", then those compatibility functions will be used for a decade. So we need to find a balance between upgrades and ongoing support. Easy upgrades will mean complex ongoing support. Complex upgrades make ongoing support easier, but also make it less likely that people will upgrade.