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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	simple isdn4linux PPP FAQ .. to be continued .. not 'debugged' 
2	-------------------------------------------------------------------
4	Q01: what's pppd, ipppd, syncPPP, asyncPPP ??
5	Q02: error message "this system lacks PPP support"
6	Q03: strange information using 'ifconfig'
7	Q04: MPPP?? What's that and how can I use it ...
8	Q05: I tried MPPP but it doesn't work 
9	Q06: can I use asynchronous PPP encapsulation with network devices
10	Q07: A SunISDN machine can't connect to my i4l system
11	Q08: I wanna talk to several machines, which need different configs
12	Q09: Starting the ipppd, I get only error messages from i4l
13	Q10: I wanna use dynamic IP address assignment 
14	Q11: I can't connect. How can I check where the problem is.
15	Q12: How can I reduce login delay? 
17	-------------------------------------------------------------------
19	Q01: pppd, ipppd, syncPPP, asyncPPP .. what is that ?
20	   what should I use?
21	A: The pppd is for asynchronous PPP .. asynchronous means
22	   here, the framing is character based. (e.g when
23	   using ttyI* or tty* devices)
25	   The ipppd handles PPP packets coming in HDLC
26	   frames (bit based protocol) ... The PPP driver
27	   in isdn4linux pushes all IP packets direct
28	   to the network layer and all PPP protocol
29	   frames to the /dev/ippp* device. 
30	   So, the ipppd is a simple external network
31	   protocol handler.
33	   If you login into a remote machine using the
34	   /dev/ttyI* devices and then enable PPP on the
35	   remote terminal server -> use the 'old' pppd
37	   If your remote side immediately starts to send
38	   frames ... you probably connect to a 
39	   syncPPP machine .. use the network device part
40	   of isdn4linux with the 'syncppp' encapsulation
41	   and make sure, that the ipppd is running and 
42	   connected to at least one /dev/ippp*. Check the 
43	   isdn4linux manual on how to configure a network device.
45	--
47	Q02: when I start the ipppd .. I only get the
48	   error message "this system lacks PPP support"
49	A: check that at least the device 'ippp0' exists.
50	   (you can check this e.g with the program 'ifconfig')
51	   The ipppd NEEDS this device under THIS name .. 
52	   If this device doesn't exists, use:
53		isdnctrl addif ippp0
54		isdnctrl encap ippp0 syncppp
55		... (see isdn4linux doc for more) ...
56	A: Maybe you have compiled the ipppd with another
57	   kernel source tree than the kernel you currently
58	   run ... 
60	--
62	Q03: when I list the netdevices with ifconfig I see, that
63	   my ISDN interface has a HWaddr and IRQ=0 and Base 
64	   address = 0 
65	A: The device is a fake ethernet device .. ignore IRQ and baseaddr
66	   You need the HWaddr only for ethernet encapsulation.
68	--
70	Q04: MPPP?? What's that and how can I use it ...
72	A: MPPP or MP or MPP (Warning: MP is also an 
73	   acronym for 'Multi Processor') stands for
74	   Multi Point to Point and means bundling
75	   of several channels to one logical stream.
76	   To enable MPPP negotiation you must call the
77	   ipppd with the '+mp' option. 
78	   You must also configure a slave device for
79	   every additional channel. (see the i4l manual
80	   for more)
81	   To use channel bundling you must first activate
82	   the 'master' or initial call. Now you can add 
83	   the slave channels with the command:
84	       isdnctrl addlink <device>
85	   e.g:
86	       isdnctrl addlink ippp0
87	   This is different from other encapsulations of
88	   isdn4linux! With syncPPP, there is no automatic
89	   activation of slave devices.
91	--
93	Q05: I tried MPPP but it doesn't work .. the ipppd
94	   writes in the debug log something like:
95	   .. rcvd [0][proto=0x3d] c0 00 00 00 80 fd 01 01 00 0a ...
96	   .. sent [0][LCP ProtRej id=0x2 00 3d c0 00 00 00 80 fd 01 ...
98	A: you forgot to compile MPPP/RFC1717 support into the
99	   ISDN Subsystem. Recompile with this option enabled.
101	--
103	Q06: can I use asynchronous PPP encapsulation
104	   over the network interface of isdn4linux ..
106	A: No .. that's not possible .. Use the standard
107	   PPP package over the /dev/ttyI* devices. You
108	   must not use the ipppd for this.
110	--
112	Q07: A SunISDN machine tries to connect my i4l system,
113	   which doesn't work.
114	   Checking the debug log I just saw garbage like:
115	!![ ... fill in the line ... ]!!
117	A: The Sun tries to talk asynchronous PPP ... i4l
118	   can't understand this ... try to use the ttyI*
119	   devices with the standard PPP/pppd package
121	A: (from Alexanter Strauss: )
122	!![ ... fill in mail ]!!
124	--
126	Q08: I wanna talk to remote machines, which need
127	   a different configuration. The only way
128	   I found to do this is to kill the ipppd and
129	   start a new one with another config to connect
130	   to the second machine. 
132	A: you must bind a network interface explicitly to
133	   an ippp device, where you can connect a (for this
134	   interface) individually configured ipppd.
136	--
138	Q09: When I start the ipppd I only get error messages
139	   from the i4l driver .. 
141	A: When starting, the ipppd calls functions which may 
142	   trigger a network packet. (e.g gethostbyname()).
143	   Without the ipppd (at this moment, it is not
144	   fully started) we can't handle this network request.
145	   Try to configure hostnames necessary for the ipppd
146	   in your local /etc/hosts file or in a way, that
147	   your system can resolve it without using an
148	   isdn/ippp network-interface.
150	--
152	Q10: I wanna use dynamic IP address assignment ... How 
153	   must I configure the network device.
155	A: At least you must have a route which forwards
156	   a packet to the ippp network-interface to trigger
157	   the dial-on-demand.
158	   A default route to the ippp-interface will work.
159	   Now you must choose a dummy IP address for your
160	   interface.
161	   If for some reason you can't set the default
162	   route to the ippp interface, you may take any 
163	   address of the subnet from which you expect your
164	   dynamic IP number and set a 'network route' for
165	   this subnet to the ippp interface.
166	   To allow overriding of the dummy address you
167	   must call the ipppd with the 'ipcp-accept-local' option.
169	A: You must know, how the ipppd gets the addresses it wanna
170	   configure. If you don't give any option, the ipppd
171	   tries to negotiate the local host address!
172	   With the option 'noipdefault' it requests an address
173	   from the remote machine. With 'useifip' it gets the
174	   addresses from the net interface. Or you set the address
175	   on the option line with the <a.b.c.d:e.f.g.h> option.
176	   Note: the IP address of the remote machine must be configured
177	   locally or the remote machine must send it in an IPCP request.
178	   If your side doesn't know the IP address after negotiation, it
179	   closes the connection!
180	   You must allow overriding of address with the 'ipcp-accept-*'
181	   options, if you have set your own or the remote address 
182	   explicitly.
184	A: Maybe you try these options .. e.g:   
186	    /sbin/ipppd :$REMOTE noipdefault /dev/ippp0
188	   where REMOTE must be the address of the remote machine (the
189	   machine, which gives you your address)
191	--
193	Q11: I can't connect. How can I check where the problem is.
195	A: A good help log is the debug output from the ipppd...
196	   Check whether you can find there:
197	   - only a few LCP-conf-req SENT messages (less then 10)
198	     and then a Term-REQ:
199	     -> check whether your ISDN card is well configured
200	        it seems, that your machine doesn't dial
201	        (IRQ,IO,Proto, etc problems)
202	        Configure your ISDN card to print debug messages and
203	        check the /dev/isdnctrl output next time. There
204	        you can see, whether there is activity on the card/line.
205	   - there are at least a few RECV messages in the log:
206	     -> fine: your card is dialing and your remote machine
207	        tries to talk with you. Maybe only a missing 
208	        authentication. Check your ipppd configuration again.
209	   - the ipppd exits for some reason:
210	     -> not good ... check /var/adm/syslog and /var/adm/daemon.
211	        Could be a bug in the ipppd.
213	--
215	Q12: How can I reduce login delay?
217	A: Log a login session ('debug' log) and check which options 
218	  your remote side rejects. Next time configure your ipppd
219	  to not negotiate these options. Another 'side effect' is, that
220	  this increases redundancy. (e.g your remote side is buggy and
221	  rejects options in a wrong way).
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