Operation Manual

Access Protection and Security Mechanisms
51 NT/MPRI – 3 Configuration and Operation of the NT/MPRI: The Basics
PAP or CHAP Authentication
For each call destination you may require that the remote site authenti-
cate itself to the local router (“Authentication at Local Site”). This au-
thentication is performed in accordance with the PAP and CHAP proto-
cols (RFCs 1334 and 1994, respectively). Both procedures require the
configuration of a name and password.
In PAP authentication, the name and password are transmitted in plain
text, and the local site checks whether these match its own settings. If
so, the call is accepted.
Under CHAP, the remote site uses a defined encryption algorithm to
generate a message from the name and a random value, and sends the
message to the local site. The local site generates a new value from the
message and the password, also using a predefined algorithm, and
sends this message back. The remote site then checks whether the val-
ue it produced from the original message and password agrees with
the value sent back by the local site. If so, the call is accepted.
If the remote site also requires authentication, the name and password
received from the administrator of the remote site can be entered in
the call destination settings (“Authentication at Remote Site”).
Authentication also serves to identify the remote site when the CLI
number check is not activated.
Security Call-back
In order to further increase LAN access security, a security call-back can
be required for each call destination in accordance with the LCP Exten-
sions (RFC 1570) or the Draft RFC “PPP Call-Back Control Protocol”. This
is specified in the call destination settings.
The call-back takes place after the call has been accepted and after
PAP/CHAP authentication, should one of these protocols be activated.
The number dialed for the security call-back is the one entered in the
call destination settings.
When a logical ISDN connection remains active after an inactivity time-
out, the security call-back is repeated each time the physical connec-
tion is restored.
IP Masquerading/Network Address Resolution (NAT)
IP masquerading fulfills two important functions for Internet connec-
tions: protection from undesired external access and the mapping of
all IP addresses in the LAN to a single, Internet-compliant IP address.
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