Re: [lwip-devel] PPP problems: IPCP (NOT) obsolete option

[David Empson]

Just a quick comment on the unexplained portion of the packet:

From: "Alain M." <address@hidden>
> Michael Head escreveu:
> > PPP: sending IPCP config i/f 0
> > PPPLINK: sendpacket totlen=26 i/f 0
> > PPPLINK: sendpacket using 0000BB65
> > --- pkt flags=x40 i/f=0 tstamp=37934 len=26 ---
> >   sect 1, len=26 addr=x800B165A rlen=1500
> > 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     flag: ??  - this is always 7E
> > address: FF   - legacy byte always FF
> > control: 03     - legacy byte always 03
> > protocol:  8021  identifies protocol  8021 is Internet Protocol Control 
> > Protocol IPCP
> >
> > code:  01  Configure request
> > identifier:  01 - aids in matching request sequence.  Changes from 
> > configure request to configure re
> > length: 0016   -  there are 22 bytes in informational field.  So CRC and 
> > Flag must be added later
> >
> > type: 03  IP Address
> > length: 06  the right length for this group
> > IP Address: 00 00 00 00  requests peer to provide this information
> >
> >
> > What does the remainder of the packet mean?
> > 81 06      !           00 00 00 00 83 06 00 00 00 00     You, Alain 
> > evidentially translated these bytes...!

Those bytes are clearly within the IPCP configure request (as indicated by 
the length of 0x0016 = 22).

I don't know what they mean and haven't found an RFC documenting them, but 
they are in the right format to be two more IP configuration options of 
types 0x81 and 0x83, with length = 6 and four zero bytes for the data.

They might be something proprietary which someone put into the the PPP IPCP 
implementation by mistake (perhaps copied blindly from another 
implementation?). Possibly coincidentally, the option types have the same 
values as "IP Addresses" and "IP Address" from the IPCP standard, with the 
high order bit set.