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Re: [lwip-users] PPP no IP address assigned

From: Sylvain Rochet
Subject: Re: [lwip-users] PPP no IP address assigned
Date: Wed, 1 Apr 2015 14:02:48 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Hello Michael,

On Wed, Apr 01, 2015 at 08:47:03AM +0200, Michael Waeber wrote:
> Hi all
> I try to integrate PPP with a GPRS modem in our system. lwIP works well
> for ethernet in our system since 3 years. Since PPP is currently
> actively developed I've upgraded from 1.4.1 to current Master
> (16.03.2015).
> The modem is connected to GPRS, then the PPP session is started. The
> communication parameters are negotiated successfully (LCP). The
> authentication is OK: Login OK. Now lwIP sends a Configuration request
> (IPCP):
> Raw:
> ff 03 80 21 01 01 00 16 03 06 00 00 00 00 81 06 00 00 00 00 83 06 00 00
> 00 00 6e db 7e
> Interpreted (Wireshark):
> Protocol: Internet Protocol Control Protocol (0x8021)
> Options: (18 bytes), IP address, Primary DNS Server IP Address,
> Secondary DNS Server IP Address
> IP address:
> Primary DNS Server IP Address:
> Secondary DNS Server IP Address:

That's a perfect IPCP request ;-)

> After this frame the communication is dead, no answer received, no other
> frame sent.
> I've tried using various combinations of
> - No auth, PAP, Chap
> - With/without VJ header compression
> Questions:
> a) Has anybody a hint why it does not work? I think the provider should
>    send a IPCP Configuration Request/Ack/Nack?

Yes, your modem should. There is no PPP inside the GSM network, the PPP 
session is only between your device and your modem over its serial link.

> b) I do not receive a callback (see pppos_create()). After a long
>    timeout I try to restart, but without success: The stack is in a
>    deadlock, I can't close the session. ppp_close(m_pSelf->ppp, true)
>    does not give a callback either. So the only solution is to reset the
>    whole system. How do I reset a hanging PPP session if no
>    communication happens?

Looks like your lwIP timeouts are not working or you don't have enough 
of them, PPP needs a lot of timeouts, could you check that first ?


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