Report an Error]
The implementation of L2TP for the E-series
router uses four levels:
- System—The router
- Destination—The remote L2TP system
- Tunnel—A direct path between the LAC and the LNS
- Session—A PPP connection in a tunnel
When the router has established destinations,
tunnels, and sessions, you can control the L2TP traffic. Making a
change to a destination affects all tunnels and sessions to that destination;
making a change to a tunnel affects all sessions in that tunnel. For
example, closing a destination closes all tunnels and sessions to
Sequence of Events on the LAC
The E-series router creates destinations, tunnels,
and sessions dynamically, as follows:
- The client initiates a PPP connection with the router.
- The router and the client exchange Link Control Protocol
(LCP) packets. For details about negotiating PPP connections, see
the Configuring Point-to-Point Protocol chapter
in JUNOSe Link Layer Configuration Guide.
- By using either a local database related to the domain
name or RADIUS authentication, the router determines either to terminate
or to tunnel the PPP connection.
- If the router discovers that it should tunnel the session,
it does the following:
- Sets up a new destination or selects an existing destination.
- Sets up a new tunnel or selects an existing tunnel.
- Opens a new session.
- The router forwards the results of the LCP negotiations
and authentication to the LNS.
A PPP connection now exists between the client
and the LNS.
The router discards received packets if the size of the variable-length,
optional offset pad field in the L2TP header is too large. The router
always supports packets that have an offset pad field of up to 16
bytes, and may support larger offset pad fields, depending on other
information in the header. This restriction is a possible, although
unlikely, cause of excessive discarding of L2TP packets.
Sequence of Events on the LNS
The E-series router sets up an LNS as follows:
- An LAC initiates a tunnel with the router.
- The router verifies that a tunnel with this LAC is valid—destination
configured, hostname and tunnel password correct.
- The router completes the tunnel setup with the LAC.
- The LAC sets up a session with the router.
- The router creates a dynamic PPP interface on top of the
- If they are enabled and present, the router takes the
proxy LCP and the proxy authentication data and passes them to PPP.
- The E-series PPP processes the proxy LCP, if it is present,
and, if acceptable, places LCP on the router in opened state without
renegotiation of LCP.
If proxy LCP is not present or not acceptable, the router negotiates
LCP with the remote system.
- The E-series PPP processes the proxy authentication data,
if it is present, and passes the data to AAA for verification. (If
the data is not present, E-series PPP requests the data from the remote
- The router passes the authentication results to the remote
Report an Error]