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

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The router does not support the following framing features:
■
Numbered mode (RFC 1663)
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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 515.
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 negotiating are the same, each side attempts to change its magic number.
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Overview
JUNOSe 11.1.x Link Layer Configuration Guide