Subject: case of failure negotiations on ppp

From: Muralidhar Rayapeddi <[email-masked]>
Date: Wed, 16 Aug 2000 20:57:49 +0530

I am bugging with fsm details in this, sorry about that.

hi,
I have two processes running at application level simulating ppp.
I want to execute a failure case where one of the ppp stack does
not respond to lcp config request but sends lcp cfg req & ack. call this
as pppA
pppB is a normal guy.

According to fsm pppA sends a lcp req and does not process pppB's
lcp req. It receives ack from pppB & so moves to ack rcvd state (7). In
this state
if timer expires for A then it sends a lcp cfg req & moves to req sent
state (6).
If it again receives an ack for this req, it does an irc and moves to
(7). So the
timer expiry does not have effect, b'cos every time the restart counter
gets
initialized. I think this looks like a while (1)
Now we will take pppB's case.
It receives a req, sends a req & correspondingly sends an ack. It will
move to
ack sent state (8). But it does not get a response  for the request it
sent, b'cos
pppA didn't process it. This times out, keeps sending lcp req and when
the timer
expires it says tlf & goes to  stopped state (3). Here if pppA sends a
lcp cfg req
(as it does), then according to fsm, it does an irc,src,sca and moves to
(8).
So pppB also continues in this loop.
So when does the link termination happen. Please clarify.

Regards,
Murali.

---

From: James Carlson <[email-masked]>
Date: Wed, 16 Aug 2000 11:41:10 -0400 (EDT)

> initialized. I think this looks like a while (1)

Right.  There are many of these cases in PPP.  Decent implementations
have to have additional counters and timers to detect and eliminate
loops.  See section 4.5 of RFC 1661.

> So when does the link termination happen. Please clarify.

The RFCs do not cover all possible things that need to be done to make
a stable and resilient implementation.

-- 
James Carlson, Internet Engineering       <[email-masked]>
SUN Microsystems / 1 Network Drive         71.234W   Vox +1 781 442 2084
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"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp