This is a bug report for ISE from a VPN developer. I do not have a contract.
Symptom:
In ISE if Require cryptobinding TLV is checked in the PEAP options (Policy > Policy Elements > Allowed Protocols), ISE will perform cryptobinding verification. The verification per se may succeed but the MPPE keys derived from the PEAP channel are wrong in this scenario.
This issue causes Windows VPN clients to fail to connect to Windows RAS servers which forwards authentication to ISE.
Explanation:
MS-PEAP requires that if cryptobinding TLV is exchanged between client and server, the inner session key should be derived from the inner EAP method. However ISE fails to do that. It always derives the key from the outer method (i.e. PEAP).
This bug is not noticeable from the ISE log because authentication and cryptobinding has succeeded, only the keys exported to the NAS are wrong, leading to VPN sessions cut off forcibly by the NAS.
