[lwip-users] PPP: IPCP bad fcs issue

[Axel Lin]

Hi list,

I'm testing a LTE module with lwIP and found always got bad fcs as below.
I dump the received data below:
Is there anything wrong in the received data?

sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=26␍␊
pppos_input[0]: got 17 bytes␍␊
7e ff 3 80 21 1 1 16 3 6 81 6 83 6 6e db 7e ␍␍␊
pppos_input[0]: Dropping bad fcs 0x4114 proto=0x8021␍␊
pppos_input_drop: pbuf len=13, addr 0x2000bfc0␍␊
sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=26␍␊
pppos_input[0]: got 17 bytes␍␊
7e ff 3 80 21 1 1 16 3 6 81 6 83 6 6e db 7e ␍␍␊
pppos_input[0]: Dropping bad fcs 0x4114 proto=0x8021␍␊
pppos_input_drop: pbuf len=13, addr 0x2000bfc0␍␊
sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=26␍␊
pppos_input[0]: got 17 bytes␍␊
7e ff 3 80 21 1 1 16 3 6 81 6 83 6 6e db 7e ␍
pppos_input[0]: Dropping bad fcs 0x4114 proto=0x8021

// another boot
sent [IPCP ConfReq id=0x1 <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=20␍␊
pppos_input[0]: got 15 bytes␍␊
7e ff 3 80 21 1 1 10 81 6 83 6 2d 61 7e ␍␍␊
pppos_input[0]: Dropping bad fcs 0xa6ff proto=0x8021
sent [IPCP ConfReq id=0x1 <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=20␍␊
pppos_input[0]: got 15 bytes␍␊
7e ff 3 80 21 1 1 10 81 6 83 6 2d 61 7e ␍␍␊
pppos_input[0]: Dropping bad fcs 0xa6ff proto=0x8021
sent [IPCP ConfReq id=0x1 <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>]␍␊
pppos_write[0]: len=20␍␊
pppos_input[0]: got 15 bytes␍␊
7e ff 3 80 21 1 1 10 81 6 83 6 2d 61 7e ␍␍␊
pppos_input[0]: Dropping bad fcs 0xa6ff proto=0x8021

Thanks,
Axel