3.1.5.2 Control Message AV Pairs
Section 4 of [RFC2661] specifies control message AV pairs.
If a received message has an AV pair with
any of the reserved bits set to 1 or,
the M bit set and a non-IETF vendor-ID value or,
an unrecognized Attribute Value or,
the M and H bits set, and the AV pair has an attribute other than the following:
Proxy Authen Name
Proxy Authen Challenge
Proxy Authen Id
Proxy Authen Response
Called Number
Calling Number
Sub-Address
Initial Received LCP CONFREQ
Last Sent LCP CONFREQ
Last Received LCP CONFREQ
ACCM
Private Group ID
then
If the control message AV pair is in a control connection management message, the control connection MUST be torn down.
If the control message AV pair is in the call session management messages, the corresponding call session MUST be torn down.
The following AV pairs are ignored if they are hidden (H bit set to 1), even if the M bit is set.
Proxy Authen Name
Proxy Authen Challenge
Proxy Authen ID
Proxy Authen Response
Called Number
Calling Number
Sub Address
Initial Received LCP CONFREQ
Last Sent LCP CONFREQ
Last Received LCP CONFREQ:
ACCM
Private Group ID
None of the AV pairs sent by LAC/LNS have the H bit set to 1.
Section 4.4 of [RFC2661] provides a list of all L2TP AV pairs, some of which are hidden.