Re: [Lsr] I-D Action: draft-ietf-lsr-isis-area-proxy-03.txt

[[e-mail]]

Hi Tony,

Thanks for your reply.
All good to me.

Thanks,
--Bruno


From: Tony Li [mailto:[e-mail]] On Behalf Of [e-mail]
Sent: Saturday, September 5, 2020 2:18 AM
To: DECRAENE Bruno TGI/OLN <[e-mail]>
Cc: [e-mail]
Subject: Re: [Lsr] I-D Action: draft-ietf-lsr-isis-area-proxy-03.txt


Hi Bruno,

Thank you for your comments.

1)

OLD: The
   advertisement in the Proxy LSP informs the remainder of the network
   that packets directed to the SID will be forwarded by one of the
   Inside Edge Nodes and the Area SID will be consumed.

NEW:

The

   advertisement in the Proxy LSP informs the outside area

   that packets directed to the SID will be forwarded to one of the

   Inside Edge Nodes and the Area SID will be consumed.

Motivation:
1)      More precise/descriptive and use the terminology defined in the draft
2)      The SID is a priori global in the outside area and hence will be forwarded by all nodes in the outside area (and not just by the Inside Edge Nodes). The destination is anycast to/toward any Inside Edge node.


Ok.



2)
§ 4.3.2.  The Area SID Sub-TLV

The Area SID Sub-TLV allows the Area Leader to advertise a prefix and

   SID



§4.4.13.  The Area SID

  The Area Leader SHOULD advertise the Area SID information in the

   Proxy LSP as a Node SID as defined in [RFC8667] Section 2.1<https://tools.ietf.org/html/rfc8667#section-2.1>.


RFC8667 requires that for a Node SID, the prefix be an IP address (/32 or /138) (rather than an IP prefix of an arbitrary length) [1].
[1] https://tools.ietf.org/html/rfc8667#section-2.1.1.2

You may want to refer to this restriction when defining the Area SID Sub-TLV in section 4.3.2 . e.g. :s/advertise a prefix/advertise an IP address. Alternatively open the option to advertise a prefix SID without the N-Flag if this is a prefix.


We are implicitly doing that by permitting a prefix.



3)
1 typo in -04 :s/ Inisde/ Inside


Fixed, thanks.



4)
OLD:
The Area Leader will generate a Proxy LSP that must be flooded across
   the Inside Area.  Inside Routers MUST ignore the contents of the
   Proxy LSP other than for flooding

My personal preference would be
NEW
The Area Leader will generate a Proxy LSP that will be flooded across
   the Inside Area.  Inside Routers MUST ignore the contents of LSP(s) originated with the Area Proxy System Identifier other than for flooding.

Motivation:
a)      Clarify that no new behavior is involved
b)      Specifies how the proxy LSP is to be identified as a proxy LSP.



?  Ignoring the contents of an LSP is a new behavior.  I propose something slightly different:

          The Area Leader will generate a Proxy LSP that will be
          flooded across the Inside Area.  Inside Routers MUST ignore
          the contents of the Proxy LSP other than for flooding.  The
          Proxy LSP uses the Area Proxy System Identifier as its Source
          ID.




5) Open question: is the Area Proxy LSP to be advertised/read from L1 or L2 LSP/LSDB or both?

“All routers within the Inside Area speak Level 1 and Level 2 IS-IS on all of the links within the topology.”
OK.

“A node advertises the Area Proxy TLV in its L2 LSP”
So my reading/guessing is that the Area Proxy TLV is only sent in the L2 LSP of all Inside routers. (i.e. not in the L1 LSP).
If so:
-          Can you clarify the behavior when an Area Proxy TLV is received in an L1 LSP? (e.g. ignore, and if not, what is the behavior when the TLV is different in L1 and L2).


We already say:

           The Area Leader MUST advertise the Area Proxy System
           Identifier Sub-TLV when it observes that all Inside Routers
           are advertising the Area Proxy TLV.

The statement that you quote is pretty clear that the Area Proxy TLV is found in the L2 LSP.  I take it that you feel that this is insufficient.
I propose to add:

         Nodes MUST NOT advertise the Area Proxy TLV in a L1 LSP. Nodes MUST
          ignore the Area Proxy TLV if it is found in a L1 LSP.



-          “they will advertise the Area Proxy TLV.” May be adding “in their L2 LSP”


Ok.



-          “All Inside Edge Routers learn the Area Proxy System Identifier from the Level 1 LSDB”. I would have assumed  “from the Area Proxy TLV advertised in the level 2 LSDB.  So it may be a typo or I’m missing something, which is very possible.


That was a bug, thanks.  I changed it to: “ … from the Area Proxy TLV advertised by the Area Leader … “



o   “it MUST inject   the Area Proxy System Identifier into the Level 1 LSDB.” Same comment.


Also a bug.  Should be L2.  Fixed.


Thanks for the detailed review!


Tony


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