431
• The Identifier field (1 byte long) is used to match request packets and response packets and to detect
duplicate request packets. Request and response packets of the same type have the same identifier.
• The Length field (2 bytes long) indicates the length of the entire packet, including the Code,
Identifier, Length, Authenticator, and Attributes fields. Bytes beyond this length are considered
padding and are ignored at the receiver. If the length of a received packet is less than this length,
the packet is dropped. The value of this field is in the range 20 to 4096.
• The Authenticator field (16 bytes long) is used to authenticate responses from the RADIUS server and
to encrypt user passwords. There are two types of authenticators: request authenticator and
response authenticator.
• The Attributes field (variable in length) carries the specific authentication, authorization, and
accounting information that defines the configuration details of the request or response. This field
may contain multiple attributes, each with three sub-fields:
{ Type—(1 byte long) Type of the attribute. It is in the range of 1 to 255. Commonly used RADIUS
attributes are defined in RFC 2865, RFC 2866, RFC 2867, and RFC 2868. Table 117 sh
ows a
list of the attributes.
{ Length—(1 byte long) Length of the attribute in bytes, including the Type, Length, and Value
sub-fields.
{ Value—(Up to 253 bytes) Value of the attribute. Its format and content depend on the Type and
Length sub-fields.
Table 117 Commonly used RADIUS attributes
No. Attribute No.
1 User-Name 45 Acct-Authentic
2 User-Password 46 Acct-Session-Time
3 CHAP-Password 47 Acct-Input-Packets
4 NAS-IP-Address 48 Acct-Output-Packets
5 NAS-Port 49 Acct-Terminate-Cause
6 Service-Type 50 Acct-Multi-Session-Id
7 Framed-Protocol 51 Acct-Link-Count
8 Framed-IP-Address 52 Acct-Input-Gigawords
9 Framed-IP-Netmask 53 Acct-Output-Gigawords
10 Framed-Routing 54 (unassigned)
11 Filter-ID 55 Event-Timestamp
12 Framed-MTU 56-59 (unassigned)
13 Framed-Compression 60 CHAP-Challenge
14 Login-IP-Host 61 NAS-Port-Type
15 Login-Service 62 Port-Limit
16 Login-TCP-Port 63 Login-LAT-Port
17 (unassigned) 64 Tunnel-Type
18 Reply-Message 65 Tunnel-Medium-Type
19 Callback-Number 66 Tunnel-Client-Endpoint