RADIUS adds two attributes, EAP-Message and Message-Authenticator, for supporting EAP authentication. For the RADIUS packet format, see "Configuring AAA."


RADIUS encapsulates EAP packets in the EAP-Message attribute, as shown in Figure 27. The Type field takes 79, and the Value field can be up to 253 bytes. If an EAP packet is longer than 253 bytes, RADIUS encapsulates it in multiple EAP-Message attributes.

Figure 27: EAP-Message attribute format


RADIUS includes the Message-Authenticator attribute in all packets that have an EAP-Message attribute to check their integrity. The packet receiver drops the packet if the calculated packet integrity checksum is different than the Message-Authenticator attribute value. The Message-Authenticator prevents EAP authentication packets from being tampered with during EAP authentication.

Figure 28: Message-Authenticator attribute format