1-4
2) The Identifier field (1-byte long) is for matching request packets and response packets and
detecting retransmitted request packets. The request and response packets of the same type have
the same identifier.
3) The Length field (2-byte long) indicates the length of the entire packet, including the Code,
Identifier, Length, Authenticator, and Attribute fields. The value of the field is in the range 20 to
4096. Bytes beyond the length are considered the padding and are neglected upon reception. If the
length of a received packet is less than that indicated by the Length field, the packet is dropped.
4) The Authenticator field (16-byte long) is used to authenticate replies from the RADIUS server, and
is also used in the password hiding algorithm. There are two kinds of authenticators: request
authenticator and response authenticator.
5) The Attribute field, with a variable length, carries the specific authentication, authorization, and
accounting information for defining configuration details of the request or response. This field is
represented in triplets of Type, Length, and Value.
z Type: One byte, in the range 1 to 255. It indicates the type of the attribute. Commonly used
attributes for RADIUS authentication, authorization and accounting are listed in
Table 1-2.
z Length: One byte for indicating the length of the attribute in bytes, including the Type, Length, and
Value fields.
z Value: Value of the attribute, up to 253 bytes. Its format and content depend on the Type and
Length fields.
Table 1-2 RADIUS attributes
No. Attribute No. Attribute
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
20 Callback-ID 67 Tunnel-Server-Endpoint
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