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Document: draft-ietf-l2tpext-sbfd-discriminator-03.txt
Reviewer: Elwyn Davies
Review Date: 2016/04/10
IETF LC End Date: 2016/04/05
IESG Telechat date: (if known) -
Summary: Almost ready. There are a number of acronyms that need
expansion and I am unclear how an implementation of S-BFD getting its
discriminators via L2TPv3 would know what entities the advertised
discriminators (whether one or many) should be associated with. This
probably just needs a single sentence to sort it out, but I found the
existing wording to be either inappropriate or just plain wrong.
Nearly Major Issue:
Question:
The format allows multiple discriminators to be sent in one message.
Looking at the S-BFD base draft (s3), it is implied that if a S-BFD
module is dealing with multiple discriminators they would be associated
with multiple different entities. How would the receiver know what
entity each of the discriminators was supposed to be associated with?
It seems to me that the receiver would want to know this but I may not
have understood what is going on here. I guess one way would be to use
a part of the discriminator bit pattern but I don't know if this might
make it more difficult to achieve uniqueness in a domain. Alternatively
a purpose provided field could be sent in addition to each
discriminator, or different AVP IDs used for well-known purposes.
The sentence at the end of para 4 of s2.1:
When multiple S-BFD discriminators are
advertised, the mechanism to choose a subset of specific
discriminator(s) is out of scope for this document.
may be associated with this question but I am not sure
(1) which end is supposed to be choosing - is the Initiator choosing
which to advertise or the Responder choosing which to 'do something
with', and
(2) it seems to me that the L2TPv3 receiver or its associated S-BFD
module would be deciding on some well-defined basis which entities were
associated with which designator rather than just making an arbitrary
choice.
I suggest that a sentence indicating how the association of
discriminators to entities is done (or even that it needs to be done but
how it is done is out of scope) needs to be added, and the sentence
above needs to be clarified or subsumed in this new part (unless either
of the more draconian alternatives suggested above is thought to be
appropriate).
Minor issues:
None
Nits/editorial comments:
Abstract: I'm afraid you are going to have expand the acronyms AVP,
L2TP and BFD here. References to RFC 5880 and the new S-BFD draft RFC
would also be helpful - in the form "(RFC 5880,
I-D.ietf-bfd-seamless-base)".
s1.1: The L2TP message names used in s2.1 and elsewhere (ICRQ, ICRP,
OCRQ, OCRP) need to be expanded - here would be as good as anywhere.
s2.1: Need to expand AVP and ID.
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