RADIUS attribute from rfc7268
The EAP-Peer-Id Attribute contains a Peer-Id generated by the EAP method. Exactly how this name is used depends on the link layer in question. See for more discussion. The EAP-Peer-Id Attribute MAY be included in Access-Request, Access-Accept, and Accounting-Request packets. More than one EAP-Peer-Id Attribute MUST NOT be included in an Access-Request; one or more EAP-Peer-Id Attributes MAY be included in an Access-Accept.It should be noted that not all link layers use this name, and existing EAP method implementations do not generate it. Since the NAS operates as a pass-through in EAP , it cannot know the EAP-Peer-Id before receiving it from the RADIUS server. As a result, an EAP-Peer-Id Attribute sent in an Access-Request MUST only contain a single NUL character. A home RADIUS server receiving an Access-Request with an EAP-Peer-Id Attribute containing anything other than a single NUL character MUST silently discard the attribute. In addition, the home RADIUS server SHOULD include one or more EAP-Peer-Id Attributes in an Access-Accept only if an EAP-Peer-Id Attribute was present in the Access-Request. If a NAS receives EAP-Peer-Id Attribute(s) in an Access-Accept without having included one in an Access-Request, the NAS SHOULD silently discard the attribute(s). A summary of the EAP-Peer-Id Attribute format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | String... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 175 Length >=3 String The String field is one or more octets, containing an EAP Peer-Id exported by the EAP method. For details, see. A robust implementation SHOULD support the field as undistinguished octets. Only a single EAP Peer-Id may be included per attribute.