[Pppext] Comment related to draft-ietf-pppext-trill-protocol-01.txt

[Donald Eastlake <[e-mail]>]

Hi,

I've received a comment about the last figure in Section 2.3 of
draft-ietf-trill-rbridge-protocol-16.txt. This figure shows a very
high level generic view of a TRILL Data frame being sent over PPP.
However, there is a possible problem with that figure.

The general form of a TRILL Data frame is
  Link Header
  TRILL Header
  Encapsulated data frame in Ethernet format
  Link Trailer

If the link is Ethernet, the Link Header is an Ethernet Header
(destination MAC, source MAC, possible VLAN tag, Ethertype) and the
Link Trailer is an Ethernet Trailer, that is, an FCS covering the
entire frame.

If the link is PPP, then we should have a PPP Header, which is fine
and is shown in the figure, but is there a "PPP Trailer"? The figure
shows an "Ethernet FCS" which may be wrongly labeled. If there is an
FCS there, calculated as Ethernet does, how much of the frame does it
cover? In particular, does it cover the PPP Header, in which case I
think it should be labeled "PPP FCS"? Or should the convention in PPP
be to have an FCS just covering the encapsulated Ethernet frame?

In any case, I think a few words about this are needed in the
pppext-trill draft...

Thanks,
Donald
=============================
 Donald E. Eastlake 3rd   [phone] (cell)
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