Catching up on NANOG after returning from IETF, I found this incongruous message, and would like to correct the misinformation. The PPP Maximum Receive Unit is negotiated, but this is a "maximum", not a "fixed" size. Smaller packets can be sent. While it would be perfectly legal to fill the remainder of the packet with padding, I know of no vendor that does it. This would seriously waste bandwidth. The padding feature is available for old chipsets that require 16-bit and 32-bit output data alignment. Further questions about PPP should be sent to the ietf-ppp@merit.edu mailing list, as designated in RFC1661.... Yes, NANOG is also hosted by Merit, but the lists have different purposes. Really. As usual, joining a list requires a message to <list>-request. I was amazed at the number of messages arising from nanog list members complaining that pppsdh@greendragon.com did not allow sending a "join", "request", "subscribe" or other subject to the mailing list directly. (heavy sigh)
From: "Chris MacFarlane" <cjm@ican.net> More to the point is that the frame size is negotiated while handshaking. Once two devices agree on the size it is fixed for the duration of the session.
-----Original Message----- From: George Janosik <gjanosik@torrentnet.com>
Is a PPP frame size static or elastic? RFC 1661 states: ... But, it also says the the Information field "MAY" be padded up to the MRU.
I have hard time believing that a PPP frame would be static.
WSimpson@UMich.edu Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32