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


From: David Empson
Subject: Re: [lwip-devel] PPP problems: IPCP (NOT) obsolete option
Date: Fri, 19 Dec 2008 11:43:38 +1300

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.





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