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

[James Carlson <[e-mail]>]

Donald Eastlake wrote:
> 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"?

It depends on the underlying link type and options (e.g., RFC 1570), but
the short answer is "yes."

> 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?

The standard PPP FCS covers the entire frame, including any HDLC and PPP
headers and user data, but without the medium-dependent bit or octet
stuffing.  See RFC 1662 for details.

Yes, it covers the same things the Ethernet FCS does.

> 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...

We don't normally do that for PPP documents -- it's assumed that the NCP
document just covers the bits that are particular to that NCP, and not
all of the common PPP bits all the way down to the bare metal -- but I
guess I can do that if it'll help with alignment with the other TRILL
documents.

(For what it's worth, I don't think the TRILL document should mention
the Ethernet FCS, either.  TRILL isn't defining Ethernet encapsulation,
and including those bits seems like duplication.  But I suppose that's
just me ...)

-- 
James Carlson         42.703N 71.076W         <[e-mail]>