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Chapter 8
Troubleshooting ISDN
In troubleshooting, the PPP protocol provides additional information
regarding the connection, including the protocol type. This rarely presents
itself in a manner that is usable to administrators, however. Rather, an
understanding of the protocol and its capability to provide useful functions,
including CHAP, is often more helpful to administrators. Note that the PPP
protocol is the same for analog or ISDN connections, so the configuration of
PPP on a workstation using an analog modem requires PPP encapsulation on
an ISDN host router. PPP also supports compression.
PPP contains protocol field values that document the upper layer infor-
mation included in the datagram. A list of some protocol field values is given
in Table 8.1.
T A B L E 8 . 1
Point-to-Point Protocol Field Values
Hex Value of Field
Protocol
0021
IP
0029
AppleTalk
002B
IPX
003D
Multilink
0201
802.1d Hellos
0203
Source Route Bridging Bridge Protocol Data Units
8021
IPCP
8029
ATCP
802B
IPXCP
C223
CHAP
C023
PAP
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