Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010 Configuration Manual page 613

NOTE: The JUNOSe software's PPP application accepts null usernames during PAP
and CHAP authentication. When the PPP application receives an authentication
request that includes a null username, PPP passes the request to AAA. To take
advantage of this feature, configure your authentication server to support the use of
null usernames.
ppp chap-challenge-length
CAUTION: Do not use the ppp chap-challenge-length command; increasing the
minimum length (from the default 16 bytes) or decreasing the maximum length
(from the default 32 bytes) reduces the security of your router.
ppp fragmentation
command specifies pap as the primary authentication protocol and chap as the
alternate.
host1(config-if)#ppp authentication pap chap
The router requests the use of PAP as the authentication protocol (because it
appears first in the command line). If the peer refuses to use PAP, the router
requests the CHAP protocol. If the peer refuses to negotiate authentication, the
router terminates the PPP session.
Example 2 Specifies a virtual router for the authentication virtual router context.
This command is available in static configurations and in profiles.
host1(config-if)#ppp authentication virtual-router boston pap chap
Use the no version to specify that the router does not require authentication.
See ppp authentication.
Use to modify the length of the CHAP challenge by specifying the minimum
length and maximum length.
Specify the minimum and maximum lengths in bytes in the range 8–63.
The maximum length must be greater than or equal to the minimum length.
Example
host1(config-profile)#ppp chap-challenge-length 24 28
Use the no version to restore the default minimum 16 bytes and default
maximum 32 bytes.
See ppp chap-challenge-length.
Use to enable fragmentation on an MLPPP link interface and optionally specify
the maximum fragment size, in octets, to be used on the link.
Example
Chapter 17: Configuring Dynamic Interfaces
Configuring a Dynamic Interface from a Profile
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