RADIUS

Name

Acct-Session-ID

Synopsis

Attribute Number	44
Length	3 or more octets
Value	STRING
Allowed in	Accounting-Request
Prohibited in	Accounting-Response
Presence in Packet	Required
Maximum Iterations	1

This attribute is used to uniquely identify a session so that accounting stop and start records can be collated and recorded accurately. There are a few considerations as to the packets that these attributes can be found in:

Accounting-Request packets

are required to have Acct-Session-ID.

Access-Request packets

are allowed to contain this attribute. If this is the case, then the RADIUS client gear is required to use the same session ID in all packets pertaining to that connection for the duration of that session.

The RFC requires that this session ID be printed using the UTF-8 10646 character set. From RFC 2866: “For example, one implementation uses a string with an 8-digit upper case hexadecimal number, [sic] the first two digits increment on each reboot (wrapping every 256 reboots) and the next 6 digits counting from 0 for the first person logging in after a reboot up to 2^24-1, about 16 million. Other encodings are possible.”

In practice, however, RADIUS client equipment tends to not send the Acct-Session-ID attributes using unique values. Many reuse these values across reboots, which can make tracking a session in its entirety using accounting data much more difficult.