Re: [lwip-users] PPP: IPCP bad fcs issue

[Patrick Klos]

On 8/15/2018 4:19 PM, Sylvain Rochet wrote:
> But what is very strange is that checksum including checksum itself for
> comparison purpose for "0x01 0x01 0x16 0x03 0x6 0x81 0x6 0x83 0x06 0x6e
> 0xdb" is 0xeb 0xbe, which is not 0x4114 (nor 0x1441 with byte swap) as
> displayed in your "Dropping bad fcs" debug print, how is that even
> possible ?

For what it's worth, 0x4114 is the complement of the byte swap 0xebbe 
(and that's how the FCS is added to a PPP packet).  I didn't look at the 
actual code to see at what stage and which value the message prints, but 
it's close enough to say it's probably right.

Patrick