Re: [bess] WG Last Call on draft-ietf-bess-evpn-etree

"Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net> Thu, 28 January 2016 01:26 UTC

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From: "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>
To: "EXT - thomas.morin@orange.com" <thomas.morin@orange.com>, BESS <bess@ietf.org>, "draft-ietf-bess-evpn-etree@tools.ietf.org" <draft-ietf-bess-evpn-etree@tools.ietf.org>
Thread-Topic: [bess] WG Last Call on draft-ietf-bess-evpn-etree
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Date: Thu, 28 Jan 2016 01:26:29 +0000
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Subject: Re: [bess] WG Last Call on draft-ietf-bess-evpn-etree
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I was involved in relevant discussions, and have reviewed once more for this LC.

I support the publication, but with the following questions/comments.

2.1 Scenario 1: Leaf OR Root site(s) per PE

   ... If the number of EVIs is very large
   (e.g., more than 32K or 64K), then RT type 0 as defined in [RFC4360]
   SHOULD be used; otherwise, RT type 2 is sufficient.

RFC 7153 should be referenced for "Type 2".

Additionally, why is 32K mentioned? I can understand the 64k part.

   ... the MPLS-encapsulated frames MUST be tagged with an
   indication of whether they originated from a Leaf AC or not.

Perhaps change the last line to "indication if they originated from a Leaf AC"? Packets from a root AC are not tagged with a leaf indication.

   Other mechanisms for identifying whether an egress AC is a root or
   leaf is beyond the scope of this document.

Should "egress" be "ingress" in the above paragraph? Or simply removed?

   ... This Leaf MPLS label is advertised to other PE devices,
   using a new EVPN Extended Community called E-TREE Extended Community
   (section 5.1) along with an Ethernet A-D per ES route with ESI of
   zero and a set of Route Targets (RTs) corresponding to all the leaf
   ACs on the PE.

Perhaps change the last sentence to "... corresponding to all EVIs that have leaf sites on the PE."

3.2.3 BUM traffic originated from a multi-homed site on a leaf AC

   In this scenario, it is assumed that a multi-homed Ethernet Segment
   (ES) can have a mixed of both leaf and root ACs with each AC
   designating a subnet (e.g., a VLAN).

I understand that different VLANs on the same ES could be roots or leaves. I suppose it's more important to say that for the same vlan, different PEs on the same ES must have the same root/leaf designation.

Perhaps the first sentence could be reworded as the following to capture the above point:

   While different ACs (VLANs) on the same ES could have different
   root/leaf designation (some being roots and some being leaves),
   the same VLAN does have the same root/leaf designation on all
   PEs on the same ES.

For the following:

   ... the PEs with Leaf sites perform MAC learning in the
   data-path over their Ethernet Segments, and advertise reachability in
   EVPN MAC Advertisement routes which are imported only by PEs with at
   least one Root site in the EVI. A PE with only Leaf sites will not
   import these routes. PEs with Root and/or Leaf sites may use the
   Ethernet A-D routes for aliasing (in the case of multi-homed
   segments) and for mass MAC withdrawal per [RFC 7432].

The above seems to contradict with the recommendation in Section 2.2. If the context is the scenario described in section 2.1 then that's fine, but the text does not have a clear context.


3.3.2 E-Tree without MAC Learning

   The PEs implementing an E-Tree service need not perform MAC learning
   when the traffic flows between Root and Leaf sites are multicast or
   broadcast.

I suppose an "only" word should be added at the end of the above sentence. 

   The fields of the IMET route are populated per the procedures defined
   in [RFC7432], and the route import rules are as described in previous
   sections.

The route import rules described in previous sections are for MAC routes, not IMET routes. Additionally, those rules may not be recommended, so might as well delete the last sentence.

Section 3.3.1 talks about BUM procedures. That is not specific to 3.3.1 though. Perhaps extract that out to a separate section, and remove the BUM text from 3.3.2 as well.

   The E-TREE Extended Community is encoded as an 8-octet value as
   follows:


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Type=0x06     | Sub-Type=0x04 | Flags(1 Octet)|               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Reserved=0   |           Leaf Label                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

I assume the octect after the flags octet is also reserved=0. Better mark it as "Reserved=0".

When it is used with Ethernet A-D per ES route, the leaf flag SHOULD be set to 0 but ignored by the receiving routers. Therefore, why not set it to 1 to be consistent the MAC/IP route case?

Thanks.
Jeffrey

> -----Original Message-----
> From: BESS [mailto:bess-bounces@ietf.org] On Behalf Of Thomas Morin
> Sent: Tuesday, January 19, 2016 3:51 AM
> To: BESS <bess@ietf.org>rg>; draft-ietf-bess-evpn-etree@tools.ietf.org
> Subject: [bess] WG Last Call on draft-ietf-bess-evpn-etree
> 
> Hello Working Group,
> 
> This email starts a Working Group Last Call on
> draft-ietf-bess-evpn-etree [1] which is considered mature and ready for
> a final working group review.
> 
> Please read the document if you haven't read the most recent version yet
> (-03), and send your comments to the list, no later than *February the
> 2nd* (2016-02-02).
> 
> This is not only a call for comments on the document, but also a call of
> support for its publication.
> 
> *Coincidentally*, we are also polling for knowledge of any IPR that
> applies to draft-ietf-bess-evpn-etree, to ensure that IPR has been
> disclosed in compliance with IETF IPR rules (see RFCs 3979, 4879, 3669
> and 5378 for more details).
> 
> *If* you are listed as a document author or contributor of
> draft-ietf-bess-evpn-etree please respond to this email and indicate
> whether or not you are aware of any relevant IPR.
> 
> Thank you,
> 
> Thomas/Martin
> 
> [1] https://datatracker.ietf.org/doc/draft-ietf-bess-evpn-etree
> 
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