Re: [Gen-art] Genart last call review of draft-ietf-bess-evpn-na-flags-05

["Rabadan, Jorge (Nokia - US/Mountain View)" <[e-mail]>]

Robert,

Thank you very much for the review. Great points.
Please see in-line with [Jorge]. All the changes will be included in the next revision.
Thank you!
Jorge

From: Robert Sparks via Datatracker <[e-mail]>
Date: Tuesday, August 18, 2020 at 6:11 PM
To: [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: Genart last call review of draft-ietf-bess-evpn-na-flags-05
Reviewer: Robert Sparks
Review result: Ready with Nits

I am the assigned Gen-ART reviewer for this draft. The General Area
Review Team (Gen-ART) reviews all IETF documents being processed
by the IESG for the IETF Chair.  Please treat these comments just
like any other last call comments.

For more information, please see the FAQ at

<https://trac.ietf.org/trac/gen/wiki/GenArtfaq>.

Document: draft-ietf-bess-evpn-na-flags-05
Reviewer: Robert Sparks
Review Date: 2020-08-18
IETF LC End Date: 2020-08-28
IESG Telechat date: Not scheduled for a telechat

Summary: Ready for publication as a Proposed Standard RFC but with nits to
address before publication

The protocol being defined seems fine, and the IANA considerations are well
constructed. I have a nagging feeling that there are new security concerns this
introduces, but haven't been able to identify anything specific. I appreciate
that the document discusses what happens when a bad-actor introduces
intentionally mis-configured flags.

Editorial Issues:

The Abstract is full of acronyms that are not universally understood, and it
buries the point of the document. Please consider rewriting to focus more
specifically on the goal of the draft (see the introduction in the shepherd's
writeup), keeping in mind that the abstract should make sense to people who
don't know yet what PE stands for. Much of what you currently have in the
Abstract can be left to the Introduction. I expect a  shorter (two or three
sentence) abstract will suit the document better.
[Jorge] we simplified the abstract as follows, hopefully it addresses your comment:
   Ethernet Virtual Private Network (EVPN) uses MAC/IP Advertisement
   routes to advertise locally learned MAC and IP addresses associated
   to host or routers.  The remote Provider Edge (PE) routers may use
   this information to populate their Address Resolution Protocol (ARP)
   or Neighbor Discovery (ND) tables and then reply locally to ARP
   Requests or Neighbor Solicitation messages on behalf of the owner of
   the IP address.  However, the information conveyed in the MAC/IP
   route may not be enough for the remote PE to reply to local ARP or ND
   requests.  This document defines an Extended Community that is
   advertised along with an EVPN MAC/IP Advertisement route and carries
   information relevant to the ARP/ND resolution, so that an EVPN PE
   implementing a proxy-ARP/ND function can reply to ARP Requests or
   Neighbor Solicitations with the correct information.



In section 3.2: The list of three things in the list under "R and O Flags
processing" are all processing steps. But the list of 6 things under "I Flag
processing" are not all processing steps. Please change the list to only
include processing steps, and move the examples and commentary to regular
paragraphs after the processing has been specified.

Consider moving the third top-level bullet in 3.2 ("MUST be ignored") to be the
first bullet, and after that bullet say "otherwise".
[Jorge] ok, section 3.2 changed as follows:

3.2.  Reception of the EVPN ARP/ND Extended Community



   In addition to the procedures specified in [RFC7432] a PE receiving a

   MAC/IP Advertisement route will process the EVPN ARP/ND Extended

   Community as follows:



   o  The R, O and I Flags MUST be ignored if they are advertised along

      with an EVPN MAC/IP Advertisement route that does not contain an

      IP (IPv4 or IPv6) address.  Otherwise they are processed as

      follows.



   o  R and O Flags processing:



      *  If the EVPN MAC/IP Advertisement route contains an IPv6 address

         and the EVPN ARP/ND Extended Community, the PE MUST add the R

         and O Flags to the ND entry in the ND or proxy-ND table and use

         that information in Neighbor Advertisements when replying to a

         Solicitation for the IPv6 address.



      *  If no EVPN ARP/ND Extended Community is received along with the

         route, the PE will add the default R and O Flags to the entry.

         The default R Flag SHOULD be an administrative choice.  The

         default O Flag SHOULD be 1.



      *  A PE MUST ignore the received R and O Flags for an EVPN MAC/IP

         Advertisement route that contains an IPv4->MAC pair.



   o  I Flag processing:



      *  A PE receiving an EVPN MAC/IP Advertisement route containing an

         IP->MAC and the I Flag set SHOULD install the IP->MAC entry in

         the ARP/ND or proxy-ARP/ND table as an "Immutable binding".

         This Immutable binding entry will override an existing non-

         immutable binding for the same IP->MAC.  The absence of the

         EVPN ARP/ND Extended Community in a MAC/IP Advertisement route

         indicates that the IP->MAC entry is not an "Immutable binding".



      *  Receiving multiple EVPN MAC/IP Advertisement routes with I=1

         for the same IP but different MAC is considered a

         misconfiguration.



      *  A PE originating an EVPN MAC/IP Advertisement route for

         IP1->MAC1 with I=1 MAY also originate the route with the Static

         bit set (in the MAC Mobility Extended Community).  In such a

         case, the IP1->MAC1 binding is not only immutable but it cannot







Rabadan, et al.           Expires March 5, 2021                 [Page 6]



Internet-Draft      EVPN Neighbor Advertisement Flags     September 2020





         move as well.  Even so, if an update for the same IP1->MAC1

         immutable and static, is received from a different PE, one of

         the two routes will be selected, as in the [RFC7432] case where

         two MAC/IP routes with Static bit are received for the same MAC

         from different PEs.



   In a situation where a host (with an IP->MAC that is configured as

   Immutable binding in the attached PE) is allowed to move between PEs

   (that is, the associated MAC is non-static), PEs can receive multiple

   MAC/IP advertisement routes for the same IP->MAC.  In such

   situations, MAC mobility procedures as in [RFC7432] dictate the

   reachability of the MAC.



   As an example of the use of the I Flag, consider PE1, PE2 and PE3 are

   attached to the same BD.  PE1 originates an EVPN MAC/IP Advertisement

   route for IP1->MAC1 with I=1; later on, PE2 also originates an EVPN

   MAC/IP Advertisement route IP1->MAC1 with a higher sequence number

   and I=1.  Then all the EVPN PEs attached to the same BD SHOULD retain

   their IP1->MAC1 ARP/ND binding but update MAC1's forwarding

   destination to PE2.  If for some reason, PE3 originates an EVPN MAC/

   IP Advertisement route for IP1->MAC2 (even with a higher sequence

   number), then the EVPN PEs in the BD SHOULD NOT update their

   IP1->MAC1 ARP/ND bindings, since IP1 is bound to MAC1 (MAC2 SHOULD

   still be programmed in the layer-2 BDs).  This is considered a

   misconfiguration in PE3.



   The use of the Flag I=1 assumes that a given IP is always bound to

   the same MAC address, and therefore the mobility procedures described

   in [I-D.ietf-bess-evpn-irb-extended-mobility] for "Host IP move to a

   new MAC" will not apply.



Editorial Nits:

I suggest deleting "refers to" in the terminology sentences. In all cases you
mean "is" and you don't need to say "is".
[Jorge] ok, removed


The last phrase in the description of Bit 4 at the end of section 2 was
difficult to read. Consider breaking the sentence into two or more.
[Jorge] ok, changed to:

   Bit 4 of the Flags field is defined as the "Immutable ARP/ND Binding

   Flag".  When set, the egress PE indicates that the IP->MAC pair sent

   in an EVPN MAC/IP Advertisement route (along with the Extended

   Community) is a configured ARP/ND entry.  The IP address in the EVPN

   MAC/IP Advertisement route can only be bound together with the MAC

   address specified in the same route.



At the end of section 3.1, "does not have any impact on" is confusing. I think
you mean "does not change"? At ", including" the sentence becomes awkward. I
suggest breaking that into a separate sentence. Perhaps "Specifically the
procedures for advertising ... are not changed."
[Jorge] good point, changed as suggested.