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[lwip-devel] [bug #60502] IPCP doesn't handle No Options from DCE

From: Barry Andrews
Subject: [lwip-devel] [bug #60502] IPCP doesn't handle No Options from DCE
Date: Sun, 2 May 2021 21:00:42 -0400 (EDT)
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:88.0) Gecko/20100101 Firefox/88.0


                 Summary: IPCP doesn't handle No Options from DCE
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: mrandini
            Submitted on: Mon 03 May 2021 01:00:41 AM UTC
                Category: PPP
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.1.1



Currently PPP to a cellular modem such as the Cinterion EC21 or Telit LE910
will not work for TCP as responses back from the server will be blocked
because of incorrect PPP negotiation.

This is 100% repeatable.  I have attached a PPP hex dump for wireshark to show
the difference in negotiation for the TIRTOS NDK PPP which works reliably
(first session in the capture) and the LWIP negotiation which fails 100% of
the time (Second negotiation).

In the IPCP I have noted that when a DCE has no options to negotiate the LWIP
IPCP stack currently rejects its request to have no options. The TIRTOS stack
ACKs this.

The TIROTS NDK works reliably with a TCP outgoing connection correctly getting
a response back through the mode, the LWIP stack sends out the TCP packet and
it is received by the server, but the response never comes back to the stack
and hence a TCP connection cannot be established.


File Attachments:

Date: Mon 03 May 2021 01:00:41 AM UTC  Name: _PPP@hex@dump@1.txt  Size: 8KiB  
By: mrandini
Wireshark format hex dump file, import with timestamp set to %M:%s., direction
included and PPP protocol


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