Re: [lwip-users] PPPoS: ppp session disconnect if hit bad fcs for LCP packet

[Axel Lin]

2017-07-11 21:50 GMT+08:00 Patrick Klos <address@hidden>:
> On 7/10/2017 5:23 AM, Axel Lin wrote:
>
> I got a dump of the data when bad fcs happened. (This time is "IP"
>
> rather than "LCP")
> 2145000028b56a4000ee06847834c111ea0a0002420050de7add4c7bd91377a8bd50107980ef410000279f7e21450001aeb56b4000ee0682f134c111ea0a0002420050de7add4c7bd91377a8bd50187980c6580000485454502f312e3120323030204f4b0d0a43616368652d433a205361742c203038204a756c20323031372031363a35363a353520474d540d0a5365727665723a206e67696e782f312e382e310d0a5365742d436f6f6b69653a20726571756573745f6d6574686f643d504f53543b20706174683d2f0d0a582d436f6e74656e742d547970652d4f7074696f6e733a206e6f736e6966660d0a582d4672616d652d4f7074696f6e733a2053414d454f524947494e0d0a582d526571756573742d49643a2061313932653536312d393461392d343630662d393539642d3464373862343730333035630d0a582d52756e74696d653a20302e3030363136340d0a582d5853532d50726f74656374696f6e3a20313b206d6f64653d626c6f636b0d0a436f6e74656e742d4c656e6774683a20300d0a436f6e6e656374696f6e3a20436c6f73650d0a0d0a6d6d7e2145000028b56c4000ee06847634c111ea0a0002420050de7add4c7d5d5f1377a8bd50117980edba0000da907e
>
> I think the complete packet is:
>
> 7e21450001aeb56b4000ee0682f134c111ea0a0002420050de7add4c7bd91377a8bd50187980c6580000485454502f312e3120323030204f4b0d0a43616368652d433a205361742c203038204a756c20323031372031363a35363a353520474d540d0a5365727665723a206e67696e782f312e382e310d0a5365742d436f6f6b69653a20726571756573745f6d6574686f643d504f53543b20706174683d2f0d0a582d436f6e74656e742d547970652d4f7074696f6e733a206e6f736e6966660d0a582d4672616d652d4f7074696f6e733a2053414d454f524947494e0d0a582d526571756573742d49643a2061313932653536312d393461392d343630662d393539642d3464373862343730333035630d0a582d52756e74696d653a20302e3030363136340d0a582d5853532d50726f74656374696f6e3a20313b206d6f64653d626c6f636b0d0a436f6e74656e742d4c656e6774683a20300d0a436f6e6e656374696f6e3a20436c6f73650d0a0d0a6d6d7e
>
> the bad fcs is a7c5
> Is there any thing wrong in above received data?
>
>
> Those 2 streams are from different packets.
>
> Have you already "un-escaped" the packet(s)?  If not, then the first packet
> is clearly not being parsed properly.  Look at the "7e21450001ae..." bytes
> (where I've split them below):
>
> 2145000028b56a4000ee06847834c111ea0a0002420050de7add4c7bd91377a8bd50107980ef410000279f
> 7e21450001aeb56b4000ee0682f134c111ea0a00024....
>
> That is clearly the start of a new IP packet.
>
> And given the length of the first packet (from the IP header), you may have
> lost some bytes from the first packet?

Hi Patrick,

I found a strange pattern (it happens 3 times)
IP total length is 430 (0x1ae) but I got pbuf len=371.
I'm wondering if it lost some packet, why it always happened whith
pppos_input_drop: pbuf len=371.

Below is part of my debug log:

pppos_netif_output[0]: proto=0x21, len = 544
2145000028767f4000ee0625693640ae650a0002420050f3cf6ca5a3780091d03d50106ce07d5d0000006f7c7e21450001ae76804000ee0623e23640ae650a0002420050f3cf6ca5a3780091d03d50186ce05bc00000485454502f312e31
ppp_input[0]: ip in pbuf len=40
pppos_input[0]: got 256 bytes
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
pppos_input[0]: got 110 bytes
656374696f6e3a20313b206d6f64653d626c6f636b0d0a436f6e74656e742d4c656e6774683a20300d0a436f6e6e656374696f6e3a20436c6f73650d0a0d0ada2a7e214500002876814000ee0625673640ae650a0002420050f3cf6ca5a4fe0091d03d50116ce07b7900003c297e
pppos_input[0]: Dropping bad fcs 0xc532 proto=0x21
pppos_input_drop: pbuf len=371, addr 0x2000fd04


pppos_input[0]: got 8 bytes
2145000028016a40
pppos_input[0]: got 172 bytes
00ee069a7d5e3640ae650a0002420050d937400928a901dad37350106cfc3a69000043707e21450001ae016b4000ee0698f73640ae650a0002420050d937400928a901dad37350186cfcaf250000485454502f312e3120323030204f4b0d0a43616368652d433a205361742c203135204a756c20323031372031303a31393a343420474d540d0a5365727665723a206e67696e782f312e382e310d0a5365742d436f6f6b69653a2072657175
ppp_input[0]: ip in pbuf len=40
pppos_input[0]: got 256 bytes
6573745f6d6574686f643d504f53543b20706174683d2f0d0a582d436f6e74656e742d547970652d4f7074696f6e733a206e6f736e6966660d0a582d4672616d652d4f7074696f6e733a2053414d454f524947494e0d0a582d526571756573742d49643a2038646230646539662d343734302d343936362d396337332d3337336565316538366166630d0a582d52756e74696d653a20302e3030313538300d0a582d5853532d50726f74656374696f6e3a20313b206d6f64653d626c6f636b0d0a436f6e74656e742d4c656e6774683a20300d0a436f6e6e656374696f6e3a20436c6f73650d0a0d0a1bd97e2145000028016c4000ee069a7c3640ae650a0002
pppos_input[0]: Dropping bad fcs 0xa809 proto=0x21
pppos_input_drop: pbuf len=371, addr 0x2000f68c

Thanks,
Axel