Routing and WAN connections
436
11.10
Establishing connection with PPP
BAT54-Rail/F..
Release
7.54
06/08
After the password has been successfully transmitted, the IPCP and/or
IPXCP network layer can be established.
IP and/or IPS packets can be transferred from the router modules to the
opened line if the negotiation of parameters is successful for at least one
of the network layers.
D Terminate phase
In the final phase the line is cleared, when the logical connections for all
protocols are cleared.
U PPP negotiation in the BAT
The progress of a PPP negotiation is logged in the devices' PPP statistics
and the protocol packets listed in detail there can be used for checking pur-
poses in the event of an error.
The PPP trace outputs offer a further method of analysis. You can use the
command
trace + ppp
to begin output of the PPP protocol frames exchanged during a terminal ses-
sion. You can perform a detailed analysis once the connection has been bro-
ken if this terminal session has been logged in a log file.
11.10.2Everything o.k.? Checking the line with LCP
The devices involved in the establishment of a connection through PPP ne-
gotiate a common behavior during data transfer. For example, they first de-
cide whether a connection can be made at all using the security procedure,
names and passwords specified.
The reliability of the line can be constantly monitored using the LCP once the
connection has been established. This is achieved within the protocol by the
LCP echo request and the associated LCP echo reply. The LCP echo re-
quest is a query in the form of a data packet which is transferred to the remote
station along with the data. The connection is reliable and stable if a valid re-
sponse to this request for information is returned (LCP echo reply). This re-
quest is repeated at defined intervals so that the connection can be
continually monitored.
What happens when there is no reply? First a few retries will be initiated to
exclude the possibility of any short-term line interference. The line will be
dropped and an alternative route sought if all the retries remain unanswered.
If, for example, the high-speed connection refuses to work, an existing ISDN
port can open the way to the Internet as a backup.
Note: During remote access of individual workstations with Windows operat-
ing systems, we recommend switching off the regular LCP requests since
these operating systems do not reply to LCP echo requests.
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