Juniper JUNOSE 11.2, Configuration Manual

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•
HDLC control field is 0x03 (to indicate unnumbered mode)
The router does not support the following framing features:
•
Numbered mode (RFC 1663)
• Autodetection of encapsulation
Error Frames
The router relies on higher-layer protocols to recover from PPP data loss. All unrecognized
protocol data units (PDUs) are discarded; however, statistics are maintained for packets
dropped.
Link Control Protocol
PPP’s Link Control Protocol (LCP) establishes a PPP link by negotiating with the PPP
peer at the other end of a proposed connection. When two routers initialize a PPP dialogue,
each router sends control packets to the peer. The control packets contain a list of LCP
options and corresponding values that the sending peer uses to define its end of the link,
such as the maximum receive unit (MRU).
LCP negotiations continue until the peers either converge (that is, reach an agreement
about values for connection parameters) or abandon attempts to establish a connection.
If you configure a PPP interface without an IP interface or profile, the router negotiates
LCP, but then terminates LCP after 2 to 3 minutes. Previously, the behavior in such a
circumstance was to negotiate LCP and then leave LCP open.
For static PPP interfaces, whenever LCP achieves a stopped state because of termination,
negotiation failure, or some other cause, it goes into passive mode and waits for the other
side of the connection to restart the negotiation process. Once in passive mode, the
router periodically attempts to negotiate with the other side according to an exponential
timeout algorithm.
For static PPP interfaces, the router waits 15 seconds, attempts negotiation, waits 30
seconds if it fails, attempts negotiation, waits 60 seconds if it fails, and so on. The timeout
periods are 15 seconds, 30 seconds, 60 seconds, 2 minutes, 4 minutes, 8 minutes, and
15 minutes. Once it reaches the 15-minute timeout, the router attempts negotiation every
15 minutes until successful. When LCP reaches the open state, the timer resets to 15
seconds.
Dynamic PPP interfaces are always torn down when LCP achieves a stopped state. For
more information, see “Configuring Dynamic Interfaces” on page 511.
LCP Negotiation Parameters
LCP can negotiate many PPP options, as follows:
• MRU size—Maximum receive unit size (always accepted).
• Magic number—Randomly generated number used to identify one end of a
point-to-point connection. Each side negotiates its magic number, taking note of each
other’s magic number. If both sides discover that the magic numbers they are
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JunosE 11.2.x Link Layer Configuration Guide