Re: [Gen-art] Review: draft-ietf-pim-join-attributes-for-lisp-05

["Stig Venaas (svenaas)" <[e-mail]>]

Hi

Thanks for the review Lucy, please see comments inline.

On 10/17/2016 12:09 PM, Lucy yong wrote:
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> Send again.  fix some template info.
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> *From:*Lucy yong
> *Sent:* Monday, October 17, 2016 1:59 PM
> *To:* A. Jean Mahoney; General Area Review Team;
> '[e-mail]'
> *Subject:* [Gen-art] Review: draft-ietf-pim-join-attributes-for-lisp-05
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> I am the assigned Gen-ART reviewer for this draft. The General Area
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> Document: draft-ietf-pim-join-attributes-for-lisp-05
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>      PIM Join Attributes for LISP environments.
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> Reviewer: Lucy Yong
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> Review Date: 17-Oct-2016
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> IETF LC End Date: 24-Oct-2016
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> IESG Telechat date:
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> Summary: This document specifies two new PIM join/prune attributes for
> facilitating PIM mcast transports across LISP sites.*//*Some issues need
> to be considered prior to publishing.
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> Major issues:
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> the draft assumes that PIM works within individual LISP sites but PIM
> mcast transport may not be supported among LISP sites. However the
> mechanism itself does not enforce a unique (unicast or mcast) underlay
> transport among LISP sites. Could some ETRs request unicast transport,
> other request multicast transport? The mechanism requires all LISP xTRs
> to run PIM protocol, right?

We are sending a PIM join and we assume that the upstream LIS xTR is
supporting PIM. This is similar to RFC 6831. If PIM is not supported,
the join message would be ignored. As we mention in section 4 we want
to allow a mixture of multicast and unicast forwarding.
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> PIM join/prune msg are designed for PIM protocol. These two attributes
> are specifically designed for LISP purpose. Any concern here? From PIM
> perspective, they are optional attributes; are they “MUST” attributes
> for LISP (mcast)?

It is possible to do multicast according to 6831 without these
attributes. As we mention in this draft, the transport attribute is
useful in telling the upstream whether to use unicast or multicast.
6831 only talks about multicast.

We also discuss in this section 5 how the ETR RLOC attribute is helpful
in determining the unicast destination address and for root-EID
mobility. As we mention, one could without the RLOC attribute instead
use the outer source address of the LISP encapsulated J/P message, but
that may not necessarily be the best/right address to use. So I think
we are explaining how one can do LISP multicast without these new
attributes, but there are benefits in using them. So in short, they are
not "MUST" attributes, but there are good reasons for using them.

> Minor issues: the draft uses many PIM and LISP terms without any
> explanation. It is hard for a reader to read it without knowledge of PIM
> and LISP protocol and terms.

We could perhaps clarify some, but I think we should expect someone
reading this in order to implement it, or in order to understand an
implementation, to have some knowledge of both PIM and LISP. At least
terms like RLOC, EID, ITR, ETR and xTR.

> It is not clear if Receiver RLOC attribute only applies to unicast
> transport or both unicast/mcast transport. Need to clarify.

Perhaps we should make this clearer. Currently we have this text in
section 5:

    To support root-EID mobility, receiver ETRs must also be tracked by
    the LISP control plane of the root ITR, regardless of the underlying
    transport.

In other words, one could choose not to use it for multicast transport,
but that means one may not be able to support root-EID mobility.
Mobility may not always be a requirement, but it often is.

> Backward compatibility, without these two attributes in a join/prune msg
> from a LISP ETR, what that mean?

An implementation could fall back to assuming multicast transport (per
6831) and the outer source address when the attributes are not present.

> Nits/editorial comments:
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> Section 1: “to be notified should the root of the
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>    distribution tree move to another site.”  Should “should” be “that”?

No, it is used a synonym of "in case" here.

> Section 5: several ‘must’ should be “MUST”

I'm not sure honestly. It is describing what implementations generally
need to do (or must), but it is not something we are specifying or
enforcing here, it is just information explaining how things generally
work.

Thanks,
Stig

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> Regards,
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> Lucy
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