comp.protocols.ppp part4 of 8 of frequently wanted information
Ignatios Souvatzis
Archive-name: ppp-faq/part4
Version: $Revision: 3.14 $
Last-modified: $Date: 1996/09/16 18:10:03 $
URL: http://cs.uni-bonn.de/ppp/part4.html
PPP questions and answers
4. MISC. PPP QUESTIONS WITH ANSWERS
Does somebody have a patent on PPP?
Is it possible to use PPP as link layer in ISDN?
My ppp does infinite configuration negotiation. What's wrong?
My ppp gets strange configure rejects. What's wrong?
What is Asychronous HDLC?
DP package: What is
str_restore: couldn't push module ldterm
4.1 Does somebody have a patent on PPP?
From: e...@msen.com (Edward Vielmetti)
Newsgroups: comp.protocols.tcp-ip,comp.unix.sysv386,comp.protocols.ppp
Subject: Re: Public domain PPP for SCO 2.0??
Date: 8 Dec 1992 06:04:52 GMT
[Somebody] wrote:
Doesn't matter. I just read (in another newsgroup) that DEC has a
patent on PPP, and is asking $5000 for a license. That means no public
domain PPP, and a rapidly increasing reluctance to support it from OEMs.
Stick with SLIP until something better comes along. This is *not*
true.
DEC has a patent application outstanding for the negotiation of a 48 bit
checksum which might be used in one of the option negotiation phases.
It is not an essential part of PPP; many implementations currently do
not use this little tiny algorithm in the way they work, and they work
just fine.
There is no indication that the 48 bit FCS will be accepted or
standardized on by the IETF - from my reading of the mailing lists
traffic that is unlikely at this point.
There are free PPPs and there will continue to be free PPPs. You will
also more likely buy PPPs as part of hardware you buy.
4.2 Is it possible to use PPP as link layer in ISDN?
[Somebody] wrote: Is it possible to use PPP as link layer in ISDN? If
yes, what about signalling? Do you need to combine PPP with the I.451
for basic call control? PPP over ISDN is described by RFC 1618. It
promotes PPP in bit-sync or in octet-sync HDLC over ISDN B-channels, or
PPP in X25 / PPP in Frame Relay over ISDN D-channel.
4.3 My ppp does infinite configuration negotiation.
What's wrong?
4.3.1 [CABLE PROBLEM]
Each other month somebody posts a question which essentially is the one
above. It could, of course, be some very strange set of configurations
options which get the ppp to never terminate the negotiation process
(typical situations listed in further down). One other possibility was
seen many times on the derivatives of public ppp for suns, namely
pppd-1.01beta and dp-2.x.
Detailed symptoms (from a posting on the net, I saw similar logfiles
some months ago):
Typical debugging log output:
Dec 18 16:11:01 pppd[1694]: Starting ppp daemon version 1.0beta patchleve
l 1
Dec 18 16:11:01 pppd[1694]: warning... not a process group leader
Dec 18 16:11:01 pppd[1694]: pgrpid = 1694
Dec 18 16:11:01 pppd[1694]: popped stream module : ttcompat
Dec 18 16:11:01 pppd[1694]: popped stream module : ldterm
Dec 18 16:11:01 pppd[1694]: Using unit ppp0
Dec 18 16:11:01 pppd[1694]: hostname = Riga
Dec 18 16:11:01 pppd[1694]: connect: ppp0 /dev/ttya
Dec 18 16:11:01 pppd[1694]: fsm_sconfreq(c021): Sent id 1.
Dec 18 16:11:01 pppd[1694]: Timeout 6194:16b38 in 3 seconds.
Dec 18 16:11:01 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 16:11:04 pppd[1694]: Alarm
Dec 18 16:11:04 pppd[1694]: fsm_sconfreq(c021): Sent id 2.
Dec 18 16:11:04 pppd[1694]: Timeout 6194:16b38 in 3 seconds.
Dec 18 16:11:04 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 16:11:04 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 16:11:07 pppd[1694]: Alarm
Dec 18 16:11:07 pppd[1694]: fsm_sconfreq(c021): Sent id 3.
Dec 18 16:11:07 pppd[1694]: Timeout 6194:16b38 in 3 seconds.
Dec 18 16:11:07 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 16:11:07 pppd[1694]: Setting itimer for 3 seconds.
... [lots of repetitious logging deleted] ...
Dec 18 17:02:24 pppd[1694]: Alarm
Dec 18 17:02:24 pppd[1694]: fsm_sconfreq(c021): Sent id 254.
Dec 18 17:02:24 pppd[1694]: Timeout 6194:16b38 in 3 seconds.
Dec 18 17:02:24 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 17:02:24 pppd[1694]: Setting itimer for 3 seconds.
Dec 18 17:02:26 pppd[1694]: Hangup
Dec 18 17:02:26 pppd[1694]: Untimeout 6194:16b38.
Dec 18 17:02:26 pppd[1694]: Setting itimer for 0 seconds.
Dec 18 17:02:26 pppd[1694]: str_restore: pushed module ldterm
Dec 18 17:02:26 pppd[1694]: str_restore: pushed module ttcompat
Dec 18 17:02:26 pppd[1694]: fcntl(F_SETFL, fdflags): Bad file number
The above final is caused by sending a SIGHUP to the pppd process
(however three successive SIGKILL's seem to be necessary to really get
rid of it).
The warning "not a process group leader" appears to be the innocent
result of a subtle coding bug, with no later effects, but I haven't
tried fixing it (variable "pid" uninitialized).
During all this, there seems to be no activity on the serial line, as
evident from an Interfaker(tm) breakout patch box. I was desperate
enough to lower the speed to 50 bps in order to verify this.
At the same time, "netstat -i" does show increasing figures for the
ppp0 interface in the "Opkts" column, but in no other column.
Solution: in all cases I could solve, it was a case of missing modem
control lines in the cables, leading to 'cts' floating to 'false'. The
LCP FSM happily sent configuration requests (they went to the serial
line driver buffer (and not out)), waited for an answer, got none, timed
out, and retried. After lots more of retries, especially on a big
machine, the send buffer finally does overflow, and ppp stops with an
error message.
You just have to connect 2,3,4,5,6,7,8 and 20 to the modem to repair it,
or to wire a reasonably complete null-modem cable. No, there is no
software hack, except when you patch the sources yourself. And that
would be a bad idea in my opinion. Even a small Sparcstation SLC can
overload any modem on a serial line, and you would get lots of
unnecessary packet drops because of that.
i.s.
4.3.2 [ADDRESS CONFIGURATION ERROR]
Each other month somebody posts a question which essentially is the one
above. It could, of course, be some very strange set of configurations
options which get the ppp to never terminate the negotiation process,
but this seems unlikely. This does happen under dp-2.3 [and probably
others, i.s.] when both sides of the link have differing opinions as to
what the 2 IP addresses should be. If the remote-address offered from
the remote side doesn't match the locally configured version then dp-2.3
will send back an REJ packet. The remote side will then resend the
original address again and the loop will continue.
To see if this is the case check the log for address REJ's. Then decode
the two hex addresses and print it out in the normal dot notation. This
is the IP address pair of what dp-2.x expected and what it got. Now
either reconfigure dp-2.x to expect this address or change the address
that the other side is sending.
Wolfgang Rupprecht <wolf...@wsrcc.com>
4.4 What is Asychronous HDLC?
It's HDLC with a character-by-character encapsulation, rather than a
bit-by-bit encapsulation. The details are discussed in the RFC1331,
appendix A. Basically, the flag character, the escape character and
(possibly) control characters are escaped by prepending the escape
character and XORing them with 0x20, while sync hdlc transparently
inserts '0' bits after sequences of 5 '1' bits to be sure to never
transmit the flag character in the frame.
A short description of the part of ISO 3309:1991 that describes async
(ISO calls it start/stop mode) HDLC is available with anonymous ftp from
ftp.uni-erlangen.de in pub/doc/ISO/english/async-HDLC.
4.5 My ppp gets strange configure rejects. What's wrong?
Every few days, s.b. posts a similar question, which melts down to the
above, when you look at it.
The symptoms are, e.g.:
Feb 6 09:04:08 steffi ppp[232]: demuxprotrej: Unrecognized Protocol-Reject
for protocol 29801!
Feb 6 09:04:09 steffi ppp[232]: demuxprotrej: Unrecognized Protocol-Reject
for protocol 67!
Feb 6 09:04:09 steffi ppp[232]: demuxprotrej: Unrecognized Protocol-Reject
for protocol 15405!
Feb 6 09:04:11 steffi ppp[232]: demuxprotrej: Unrecognized Protocol-Reject
for protocol 15405!
...
Pre-ppp-2.1 implementations (I think); this includes dp-2.x and probably
early dp-3.x'es are too stupid to detect the old (RFC1172) vs. new (RFC
1332 and later) format of VJ compression, although it differs in the
length and the length is explicit in each option. They tend to be off by
2 bytes after seeing such an option, and doing horrible things to
logfiles, like the cited ones.
dp-2.x users should use DP_ARGS=vjmode,draft for talking to nearly
everything, or switch to ppp-2.1.2 if they don't need autodialup in the
next few months.
The faulty side is the other one.
4.6 DP package> When the link goes down,
I get "str_restore: couldn't push module xxx"... What's wrong?
On DP-anything (at least) on SunOS 4.x, when the link goes down, you
often get these messages:
Aug 42 01:02:03 machine ppp[181]: str_restore: couldn't push module ldterm:
No such device or address
Aug 42 01:02:03 machine ppp[181]: str_restore: couldn't push module ttcompa
t: No such device or address
I guess this is pretty normal. The tty line in question was configured
to create the hangup condition on loss of carrier. The hangup condition
made the OS disconnect the tty device from the program, send the program
a SIGHUP signal, and reinitialize the tty line as a normal tty (thats
what ldterm and ttcompat are for). DP gets the SIGHUP, tries to clean up
itself (popping its own stream modules and pushing the ones it found
there when it started) and can't do it any longer.
Maybe dp could detect the condition and not complain, or not try to
clean up itself; but there might be a misjudgement of the situation,
leaving the tty without the streams modules, or with dp's own... this
would be a disaster: you could never again use them from innocent
programs like getty, login, or kermit.
The way it is now, if it can restore the tty to a sane state, it will;
if it can't, at least it tried.
i.s.
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