[bess] shepherd review of draft-ietf-bess-evpn-etree

[Thomas Morin <[e-mail]>]

Hi,

Here is the review I did while preparing the shepherd write-up for 
draft-ietf-bess-evpn-etree .

There is one thing that stands out: the document uses the most 
significant bit of the "PMSI Tunnel Attribute" Tunnel Type  field, which 
cant't be done I think without updating the structure of the 
corresponding registry (RFC7385).  I suggest how that can be done at the 
end of this review (a few people Cc'd for this reason).

Please find my comments below...

[...]

> 2  E-Tree Scenarios and EVPN / PBB-EVPN Support
>
>    In this section, we will categorize support for E-Tree into three
>    different scenarios, depending on the nature of the site association
>    (Root/Leaf) per PE or per Ethernet Segment:
>
>    - Leaf OR Root site(s) per PE
>
>    - Leaf OR Root site(s) per AC
>
>    - Leaf OR Root site(s) per MAC
>
> 2.1 Scenario 1: Leaf OR Root site(s) per PE

>
>    In this scenario, a PE may receive traffic from either Root sites OR
>    Leaf sites for a given MAC-VRF/bridge table, but not both
>    concurrently. In other words, a given EVI on a PE is either
>    associated with a root or leaf.

s/with a root or leaf/with roots or leaves/ ?


> The PE may have both Root and Leaf

s/both Root and Leaf/both Roots and Leaves/ ?


>    sites albeit for different EVIs.

>
>                    +---------+            +---------+
>                    |   PE1   |            |   PE2   |
>     +---+          |  +---+  |  +------+  |  +---+  | +---+
>     |CE1+---ES1----+--+   |  |  | MPLS |  |  | +--+----ES2-----+CE2|
>     +---+  (Root)  |  |MAC|  |  |  /IP |  |  |MAC|  |   (Leaf) +---+
>                    |  |VRF|  |  |      |  |  |VRF|  |
>                    |  |   |  |  |      |  |  |   |  | +---+
>                    |  |   |  |  |      |  |  | +--+----ES3-----+CE3|
>                    |  +---+  |  +------+  |  +---+  |   (Leaf) +---+
>                    +---------+            +---------+
>
>    Figure 1: Scenario 1
>
>    In such scenario, an EVPN PE implementation MAY provide E-TREE
>    service using topology constraint among the PEs belonging to the same

"topology constraint" is a bit opaque as a term, perhaps "using tailored 
BGP RT import/export policies" would be more descriptive (assuming I 
understood your intent)


>    EVI. The purpose of this topology constraint is to avoid having PEs
>    with only  Leaf sites importing and processing BGP MAC routes from
>    each other. To support such topology constrain in EVPN, two BGP
>    Route-Targets (RTs) are used for every EVPN Instance (EVI): one RT is
>    associated with the Root sites and the other is associated with the
>    Leaf sites. On a per EVI basis, every PE exports the single RT
>    associated with its type of site(s). Furthermore, a PE with Root
>    site(s) imports both Root and Leaf RTs, whereas a PE with Leaf
>    site(s) only imports the Root RT.

The text seems to imply that the above is sufficient to deliver the 
service, but I fail to see what would prevent Leaf-to-Leaf traffic 
between Leaves bound to the same MAC-VRF (ES2 and ES3 in firgure1).  
Shouldn't the text mention the use of a split-horizon in Leaf MAC-VRFs ?

(assuming the previous point is resolved:)

With this mechanism above, isn't it possible to have on a given PE, for 
a single E-TREE EVI, both Leaves and Roots, as long as distinct MAC-VRFs 
are used (one for Leaves and one for Roots) ? (it seems to me that the 
assymetric import/export RT would do what is needed to build an E-TREE, 
we would just have a particular case where a Leaf MAC-VRF and a Root 
MAC-VRF for a given E-TREE end up on a single PE)

If this is not possible, I think the text should explain why.


> If the number of EVIs is very large
>    (e.g., more than 64K), then RT type 0 as defined in [RFC4360] SHOULD
>    be used; otherwise, RT type 2 is sufficient [RFC7153].

This is not specific to E-VPN E-TREE, or even to E-VPN, why mention that ?


>
> 2.2 Scenario 2: Leaf OR Root site(s) per AC
>
>    In this scenario, a PE receives traffic from either Root OR Leaf
>    sites (but not both) on a given Attachment Circuit (AC) of an EVI. In
>    other words, an AC (ES or ES/VLAN) is either associated with a Root
>    or Leaf (but not both).

s/with a Root or Leaf/with Roots or Leaves/ ?



>
>                      +---------+            +---------+
>                      |   PE1   |            |   PE2   |
>     +---+            |  +---+  |  +------+  |  +---+  | +---+
>     |CE1+-----ES1----+--+   |  |  |      |  |  | +--+---ES2/AC1--+CE2|
>     +---+    (Leaf)  |  |MAC|  |  | MPLS |  |  |MAC|  |   (Leaf) +---+
>                      |  |VRF|  |  |  /IP |  |  |VRF|  |
>                      |  |   |  |  |      |  |  |   |  | +---+
>                      |  |   |  |  |      |  |  | +--+---ES2/AC2--+CE3|
>                      |  +---+  |  +------+  |  +---+  |   (Root) +---+
>                      +---------+            +---------+
>
>    Figure 2: Scenario 2
>
>    In this scenario, if there are PEs with only root (or leaf) sites per
>    EVI, then the RT constrain procedures described in section 2.1 can
>    also be used here. However, when a Root site is added to a Leaf PE,
>    then that PE needs to process MAC routes from all other Leaf PEs and
>    add them to its forwarding table. 

This is the case in 2.1 as well, isn't it ?


> For this scenario, if for a given
>    EVI, the majority of PEs will eventually have both Leaf and Root
>    sites attached, even though they may start as Root-only or Leaf-only
>    PEs, then it is recommended to use a single RT per EVI and avoid
>    additional configuration and operational overhead.

Why this recommendation ?
Even with a majority of PEs having both Leaves and Roots, there can 
remain (up to 49% of) PEs having only Leaves, which will uselessly have 
all routes to other Leaves.

So "it is recommended" above, deserves to be explained more, I think.



>
> 2.3 Scenario 3: Leaf OR Root site(s) per MAC
>
>    In this scenario, a PE may receive traffic from both Root AND Leaf
>    sites on a given Attachment Circuit (AC) of an EVI. Since an
>    Attachment Circuit (ES or ES/VLAN) carries traffic from both Root and
>    Leaf sites, the granularity at which Root or Leaf sites are
>    identifies 

s/identifies/identified/


> is on a per MAC address. This scenario is considered in
>    this draft for EVPN service with only known unicast traffic - i.e.,
>    there is no BUM traffic.

"there is no BUM" is quite a bold claim ! :=

Maybe the text should say "no BUM traffic is supported (BUM traffic will 
be dropped)" ?

(possibly "BUM traffic from Leaves will be dropped" would be sufficient ?)


>
>                      +---------+            +---------+
>                      |   PE1   |            |   PE2   |
>     +---+            |  +---+  |  +------+  |  +---+  | +---+
>     |CE1+-----ES1----+--+   |  |  |      |  |  | +--+---ES2/AC1--+CE2|
>     +---+    (Root)  |  | E |  |  | MPLS |  |  | E |  | (Leaf/Root)+---+
>                      |  | V |  |  |  /IP |  |  | V |  |
>                      |  | I |  |  |      |  |  | I |  | +---+
>                      |  |   |  |  |      |  |  | +--+---ES2/AC2--+CE3|
>                      |  +---+  |  +------+  |  +---+  |   (Leaf) +---+
>                      +---------+            +---------+
>
>    Figure 3: Scenario 3
>
> 3 Operation for EVPN
>
>    [RFC7432] defines the notion of ESI MPLS label used for split-horizon
>    filtering of BUM traffic at the egress PE. Such egress filtering
>    capabilities can be leveraged in provision of E-TREE services as seen
>    shortly. In other words, [RFC7432] has inherent capability to support
>    E-TREE services without defining any new BGP routes but by just
>    defining a new BGP Extended Community for leaf indication as shown
>    later in this document.
>
> 3.1 Known Unicast Traffic
>
>    Since in EVPN, MAC learning is performed in control plane via
>    advertisement of BGP routes, the filtering needed by E-TREE service
>    for known unicast traffic can be performed at the ingress PE, thus
>    providing very efficient filtering and avoiding sending known unicast
>    traffic over MPLS/IP core to be filtered at the egress PE as done in
>    traditional E-TREE solutions (e.g., E-TREE for VPLS).
>
>    To provide such ingress filtering for known unicast traffic, a PE
>    MUST indicate to other PEs what kind of sites (root or leaf) its MAC
>    addresses are associated with by advertising a leaf indication flag
>    (via an Extended Community) along with each of its MAC/IP
>    Advertisement route. The lack of such flag indicates that the MAC
>    address is associated with a root site. 



>   This scheme applies to all
>    scenarios described in section 2.
>
>    Furthermore, for multi-homing scenario of section 2.2, where an AC is
>    either root or leaf (but not both), the PE MAY advertise leaf
>    indication along with the Ethernet A-D per EVI route. This
>    advertisement is used for sanity checking in control-plane to ensure
>    that there is no discrepancy in configuration among different PEs of
>    the same redundancy group. For example, if a leaf site is multi-homed
>    to PE1 an PE2, and PE1 advertises the Ethernet A-D per EVI
>    corresponding to this leaf site with the leaf-indication flag but PE2
>    does not, then the receiving PE notifies the operator of such
>    discrepancy and ignore the leaf-indication flag on PE1. In other
>    words, in case of discrepancy, the multi-homing for that pair of PEs
>    is assumed to be in default "root" mode for that <ESI, EVI> or <ESI,
>    EVI/VLAN>. The leaf indication flag on Ethernet A-D per EVI route
>    tells the receiving PEs that all MAC addresses associated with this
>    <ESI, EVI> or <ESI, EVI/VLAN> are from a leaf site. Therefore, if a
>    PE receives a leaf indication for an AC via the Ethernet A-D per EVI
>    route but doesn't receive a leaf indication in the corresponding MAC
>    route, 

"MAC route" --> "MAC/IP Advertisement route" ?



> then it notify the operator and ignore the leaf indication on

s/notify/notifies/

>    the Ethernet A-D per EVI route.


The procedure above should I think be rephrased to provide unambiguous 
interpretation in the case where a given MAC is being announced in more 
than one MAC/IP advertisement route, possibly carrying a different leaf 
indication (and even possibly from different ESes, or from PEs not 
advertising Ethernet A-D route).


>
>    Tagging MAC addresses with a leaf indication enables remote PEs to
>    perform ingress filtering for known unicast traffic - i.e., on the
>    ingress PE, the MAC destination address lookup yields, in addition to
>    the forwarding adjacency, a flag which indicates whether the target
>    MAC is associated with a Leaf site or not. 

Ditto, more or less: the procedure above should I think be rephrased to 
provide unambiguous interpretation in the case where a given MAC is 
being announced in more than one MAC/IP advertisement route, possibly 
carrying a different leaf indication.

> The ingress PE cross-
>    checks this flag with the status of the originating AC, and if both
>    are Leafs, then the packet is not forwarded.



>
>    To support the above ingress filtering functionality, a new E-TREE
>    Extended Community with a Leaf indication flag is introduced [section
>    5.2]. This new Extended Community MUST be advertised with MAC/IP
>    Advertisement route and MAY be advertised with an Ethernet A-D per
>    EVI route as described above.
>
> 3.2 BUM Traffic
>
>    For BUM traffic, it is not possible to perform filtering on the
>    ingress PE, as is the case with known unicast, because of the multi-
>    destination nature of the traffic.

Saying "it is not possible" without more explanation is not very useful 
(the reader may think about using RPF-like techniques on the egress PE).
It seems to me more reasonable to formulate things in terms of "This 
specification does not provide support for filtering BUM traffic on the 
ingress PE", and avoid a sentence like the one above.

> As such, the solution relies on
>    egress filtering. In order to apply the proper egress filtering,
>    which varies based on whether a packet is sent from a Leaf AC or a
>    root AC, the MPLS-encapsulated frames MUST be tagged with an
>    indication when they originated from a Leaf AC. In other words, leaf
>    indication for BUM traffic is done at the granularity of AC. This can
>    be achieved in EVPN through the use of a MPLS label where it can be
>    used to either identify the Ethernet segment of origin per [RFC7432]
>    (i.e., ESI label) or it can be used to indicate that the packet is
>    originated from a leaf site (Leaf label).
>
>    BUM traffic sent over a P2MP LSP or ingress replication, may need to
>    carry an upstream assigned or downstream assigned MPLS label
>    (respectively) for the purpose of egress filtering to indicate to the
>    egress PEs whether this packet is originated from a leaf AC.
>
>    The main difference between downstream and upstream assigned MPLS
>    label is that in case of downstream assigned not all egress PE
>    devices need to receive the label just like ingress replication
>    procedures defined in [RFC7432].
>
>    There are four scenarios to consider as follow. 

s/follow/follows/

> In all these
>    scenarios, the imposition PE imposes the right MPLS label associated

s/the imposition PE imposes/the ingress PE imposes/ ?

>    with the originated Ethernet Segment (ES) depending on whether the
>    Ethernet frame originated from a Root or a Leaf site on that Ethernet
>    Segment (ESI or Leaf label). 

> The mechanism by which the PE identifies
>    whether a given frame originated from a Root or a Leaf site on the
>    segment is based on the Ethernet Tag associated with the frame (e.g.,
>    whether the frame received on a leaf or a root AC). 

First comment: it seems that the formulation should also support the 
case where an AC does not use .1q.

(side comment: doing the identification based on the source MAC address 
would seem to allow BUM in the context of 2.3; it is out of the scope of 
my review to extend the scope of these specs, but I'm curious why it is 
not proposed....)

> Other mechanisms
>    for identifying whether an ingress AC is a root or leaf is beyond the
>    scope of this document.
>
> 3.2.1 BUM traffic originated from a single-homed site on a leaf AC
>
>    In this scenario, the ingress PE adds a special MPLS label indicating
>    a Leaf site. This special Leaf MPLS label, used for single-homing
>    scenarios, is not on a per ES basis but rather on a per PE basis -
>    i.e., a single Leaf MPLS label is used for all single-homed ES's on
>    that PE. This Leaf 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 EVIs on the PE with
>    at least one leaf site per EVI. The set of Ethernet A-D per ES routes
>    may be needed if the number of Route Targets (RTs) that need to be
>    sent exceed the limit on a single route per [RFC7432]. The ESI for
>    the Ethernet A-D per ES route is set to zero to indicate single-homed
>    sites.
>
>    When a PE receives this special Leaf label in the data path, it
>    blocks the packet if the destination AC is of type Leaf; otherwise,
>    it forwards the packet.
>
> 3.2.2 BUM traffic originated from a single-homed site on a root AC
>
>    In this scenario, the ingress PE does not add any ESI or Leaf label
>    and it operates per [RFC7432] procedures.
>
> 3.2.3 BUM traffic originated from a multi-homed site on a leaf AC
>
>    In this scenario, it is assumed that While different ACs (VLANs) on

s/While/while/

>    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. Furthermore, it is
>    assumed that there is no forwarding among subnets - ie, the service
>    is EVPN L2 and not EVPN IRB. IRB use case is outside the scope of
>    this document.
>
>    In such scenarios,  If a multicast packet is originated from a leaf

s/multicast/multicast or broadcast/ ?

>    AC, then it only needs to carry Leaf label described in section
>    3.2.1. This label is sufficient in providing the necessary egress
>    filtering of BUM traffic from getting sent to leaf ACs including the
>    leaf AC on the same Ethernet Segment.
>
> 3.2.4 BUM traffic originated from a multi-homed site on a root AC
>
>    In this scenario, both the ingress and egress PE devices follows the
>    procedure defined in [RFC7432] for adding and/or processing an ESI
>    MPLS label.
>
> 3.3 E-TREE Traffic Flows for EVPN
>
>    Per [RFC7387], a generic E-Tree service supports all of the following
>    traffic flows:
>
>         - Ethernet Unicast from Root to Roots & Leaf
>         - Ethernet Unicast from Leaf to Root
>         - Ethernet Broadcast/Multicast from Root to Roots & Leafs
>         - Ethernet Broadcast/Multicast from Leaf to Roots
>
>    A particular E-Tree service may need to support all of the above
>    types of flows or only a select subset, depending on the target
>    application. In the case where unicast flows need not be supported,
>    the L2VPN PEs can avoid performing any MAC learning function.
>
>    In the subsections that follow, we will describe the operation of
>    EVPN to support E-Tree service with and without MAC learning.
>
> 3.3.1 E-Tree with MAC Learning
>
>    The PEs implementing an E-Tree service must perform MAC learning when
>    unicast traffic flows must be supported among Root and Leaf sites. In
>    this case, the PE with Root sites performs MAC learning in the data-

s/the PE with Root sites/the PEs with Root sites/ ?
(or "PE(s)"...)

>    path over the Ethernet Segments, and advertises reachability in EVPN
>    MAC Advertisement routes. These routes will be imported by all PEs
>    for that EVI (i.e., PEs that have Leaf sites as well as PEs that have
>    Root sites). Similarly, the PEs with Leaf sites perform MAC learning
>    in the data-path over their Ethernet Segments, and advertise
>    reachability in EVPN MAC Advertisement routes. For the scenario
>    described in section 2.1 (or possibly section 2.2), these routes are
>    imported only by PEs with at least one Root site in the EVI - i.e., 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
>    [RFC7432].
>
>    To support multicast/broadcast from Root to Leaf sites, either a P2MP
>    tree rooted at the PE(s) with the Root site(s) or ingress replication
>    can be used. The multicast tunnels are set up through the exchange of
>    the EVPN Inclusive Multicast route, as defined in [RFC7432].
>
>    To support multicast/broadcast from Leaf to Root sites, ingress
>    replication should be sufficient for most scenarios where there are
>    only a few Roots (typically two). Therefore, in a typical scenario, a
>    root PE needs to support both a P2MP tunnel in transmit direction
>    from itself to leaf PEs and at the same time it needs to support
>    ingress-replication tunnels in receive direction from leaf PEs to
>    itself. In order to signal this efficiently from the root PE, a new
>    composite tunnel type is defined per section 5.3.  This new composite
>    tunnel type is advertised by the root PE to simultaneously indicate a
>    P2MP tunnel in transmit direction and an ingress-replication tunnel
>    in the receive direction for the BUM traffic.
>
>    If the number of Roots is large, P2MP tunnels originated at the PEs
>    with Leaf sites may be used and thus there will be no need to use the
>    modified PMSI tunnel attribute in section 5.2 for composite tunnel
>    type.
>
> 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 only multicast
>    or broadcast. In this case, the PEs do not exchange EVPN MAC
>    Advertisement routes. Instead, the Inclusive Multicast Ethernet Tag
>    (IMET) routes are used to support BUM traffic.

It's nicer to avoid "acronym soup" when possible.
Here the acronym is used only once... Using  "Inclusive Multicast 
Ethernet Tag route" in these two places is ok I think.

>
>    The fields of the IMET route are populated per the procedures defined
>    in [RFC7432], and the multicast tunnel setup criteria are as
>    described in the previous section.
>
>    Just as in the previous section, if the number of PEs with root sites
>    are only a few and thus ingress replication is desired from leaf PEs
>    to these root PEs, then the modified PMSI attribute as defined in
>    section 5.3 should be used.
>
> 4 Operation for PBB-EVPN
>
>    In PBB-EVPN, the PE advertises a Root/Leaf indication along with each
>    B-MAC Advertisement route, to indicate whether the associated B-MAC
>    address corresponds to a Root or a Leaf site. Just like the EVPN
>    case, the new E-TREE Extended Community defined in section [5.1] is
>    advertised with each MAC Advertisement route.
>
>    In the case where a multi-homed Ethernet Segment has both Root and
>    Leaf sites attached, two B-MAC addresses are advertised: one B-MAC
>    address is per ES as specified in [RFC7623] and implicitly denoting
>    Root, and the other B-MAC address is per PE and explicitly denoting
>    Leaf. The former B-MAC address is not advertised with the E-TREE
>    extended community but the latter B-MAC denoting Leaf is advertised
>    with the new E-TREE extended community where "Leaf-indication" flag
>    is set. In such multi-homing scenarios where and Ethernet Segment has
>    both Root and Leaf ACs, it is assumed that 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. Furthermore, it
>    is assumed that there is no forwarding among subnets - ie, the
>    service is L2 and not IRB. IRB use case is outside the scope of this
>    document.
>
>    The ingress PE uses the right B-MAC source address depending on
>    whether the Ethernet frame originated from the Root or Leaf AC on
>    that Ethernet Segment. The mechanism by which the PE identifies
>    whether a given frame originated from a Root or Leaf site on the
>    segment is based on the Ethernet Tag associated with the frame. Other
>    mechanisms of identification, beyond the Ethernet Tag, are outside
>    the scope of this document.
>
>    Furthermore, a PE advertises two special global B-MAC addresses: one
>    for Root and another for Leaf, and tags the Leaf one as such in the
>    MAC Advertisement route. These B-MAC addresses are used as source
>    addresses for traffic originating from single-homed segments. The B-
>    MAC address used for indicating Leaf sites can be the same for both
>    single-homed and multi-homed segments.
>
> 4.1 Known Unicast Traffic
>
>    For known unicast traffic, the PEs perform ingress filtering: On the
>    ingress PE, the C-MAC destination address lookup yields, in addition
>    to the target B-MAC address and forwarding adjacency, a flag which
>    indicates whether the target B-MAC is associated with a Root or a
>    Leaf site. The ingress PE cross-checks this flag with the status of
>    the originating site, and if both are a Leaf, then the packet is not
>    forwarded.
>
> 4.2 BUM Traffic
>
>    For BUM traffic, the PEs must perform egress filtering. When a PE
>    receives a MAC advertisement route (which will be used as a source B-
>    MAC), it updates its Ethernet Segment egress filtering function

The "its Ethernet Segment egress filtering function" phrase makes it 
sounds like we're talking about a wellknown function defined somewhere.
If this is indeed the case, providing a reference would be in order.
If not, then explaining what this function is would be required.

(Are you talking about doing something similar to what 3.2 specifies for 
the non-PBB procedures ?)

>    (based on the source B-MAC address), as follows:
>
>    - If the MAC Advertisement route indicates that the advertised B-MAC
>    is a Leaf, and the local Ethernet Segment is a Leaf as well, then the
>    source B-MAC address is added to the B-MAC filtering list.

Implicitly we can guess that this "filtering list" is a list of things 
to include, rather than a list of things to include, but the text should 
I think be explicit.

>
>    - Otherwise, the B-MAC filtering list is not updated.
>
>    When the egress PE receives the packet, it examines the B-MAC source
>    address to check whether it should filter or forward the frame. Note
>    that this uses the same filtering logic as baseline [RFC7623] and
>    does not require any additional flags in the data-plane.
>
>    The PE places all Leaf Ethernet Segments of a given bridge domain in
>    a single split-horizon group in order to prevent intra-PE forwarding
>    among Leaf segments.

As per a previous comment: isn't this something that should be common 
between the EVPN and the PBB-EVPN procedures ?

> This split-horizon function applies to BUM
>    traffic.

Does it mean "only" ?
(if yes, please be explicit, and if no, adding "as well" or something 
like that would be better)


> 4.3 E-Tree without MAC Learning
>
>    In scenarios where the traffic of interest is only Multicast and/or
>    broadcast, the PEs implementing an E-Tree service do not need to do
>    any MAC learning. In such scenarios the filtering must be performed
>    on egress PEs. For PBB-EVPN, the handling of such traffic is per
>    section 4.2 without C-MAC learning part of it at both ingress and
>    egress PEs.
>
> 5 BGP Encoding
>
>    This document defines two new BGP Extended Community for EVPN.
>
> 5.1 E-TREE Extended Community
>
>    This Extended Community is a new transitive Extended Community having
>    a Type field value of 0x06 (EVPN) and the Sub-Type 0x05. It is used
>    for leaf indication of known unicast and BUM traffic. For BUM
>    traffic, the Leaf Label field is set to a valid MPLS label and this
>    EC is advertised along with Ethernet A-D per ES route with an ESI of
>    zero to enable egress filtering on disposition PEs per section 3.2.1
>    and 3.2.3. There is no need to send ESI Label Extended Community when
>    sending Ethernet A-D per ES route with an ESI of zero. For known
>    unicast traffic, the Leaf flag bit is set to one and this EC is
>    advertised along with MAC/IP Advertisement route per section 3.1.
>
>    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=0x05 | Flags(1 Octet)| Reserved=0   |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>        |  Reserved=0   |           Leaf Label                          |
> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
>
>    The low-order bit of the Flags octet is defined as the "Leaf-
>    Indication" bit. A value of one indicates a Leaf AC/Site.
>
>    When this EC is advertised along with MAC/IP Advertisement route (for
>    known unicast traffic), the Leaf-Indication flag MUST be set to one
>    and Leaf Label is set to zero. The received PE should ignore Leaf
>    Label and only processes Leaf-Indication flag. A value of zero for
>    Leaf-Indication flag is invalid when sent along with MAC/IP
>    advertisement route and an error should be logged.
>
>    When this EC is advertised along with Ethernet A-D per ES route (with
>    ESI of zero) for BUM traffic, the Leaf Label MUST be set to a valid
>    MPLS label and the Leaf-Indication flag should be set to zero. The
>    received PE should ignore the Leaf-Indication flag. A non-valid MPLS
>    label when sent along with the Ethernet A-D per ES route, should be
>    logged as an error.
>
> 5.2 PMSI Tunnel Attribute
>
>    [RFC6514] defines PMSI Tunnel attribute which is an optional
>    transitive attribute with the following format:
>
>          +---------------------------------+
>          |  Flags (1 octet)                |
>          +---------------------------------+
>          |  Tunnel Type (1 octets)         |
>          +---------------------------------+
>          |  MPLS Label (3 octets)          |
>          +---------------------------------+
>          |  Tunnel Identifier (variable)   |
>          +---------------------------------+
>
>    This draft uses all the fields per existing definition except for the
>    following modifications to the Tunnel Type and Tunnel Identifier:
>
>    When receiver ingress-replication label is needed, the high-order bit
>    of the tunnel type field (C bit - Composite tunnel bit) is set while
>    the remaining low-order seven bits indicate the tunnel type as
>    before. When this C bit is set, the "tunnel identifier" field would
>    begin with a three-octet label, followed by the actual tunnel
>    identifier for the transmit tunnel.  PEs that don't understand the
>    new meaning of the high-order bit would treat the tunnel type as an
>    invalid tunnel type. For the PEs that do understand the new meaning
>    of the high-order, if ingress replication is desired when sending BUM
>    traffic, the PE will use the the label in the Tunnel Identifier field
>    when sending its BUM traffic.

I think we should have some text to unambiguously state that: "Using the 
Composite flag for Tunnel Types 0x00 'no tunnel information present' and 
0x06 'Ingress Replication' is invalid, and should be treated as an 
invalid tunnel type on reception".

Additionally, since RFC7385 has created a registry for PMSI Tunnel 
attribute tunnel types, taking the most significant bit from this field 
can't be done without a significant change of how this registry is 
organized  (because now you can't take value in 0x7b-0x7f without 
colliding into values which are Experimental or Reserved).

Achieving the above requires an update of RFC7385, so I would suggest 
adding an 8.1 section saying this:

---
The "P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types" 
registry in the "Border Gateway Protocol (BGP) Parameters" registry 
needs to be updated to reflect the use of the most significant bit to 
advertise the use of "composite tunnels" (section 5.2).

For this purpose, this document updates RFC7385.

The registry is to be updated, by removing the entries for 0xFB-0xFE and 
0x0F, and replacing them by:
- 0x7B-0x7E Reserved for Experimental Use [this document]
- 0x7F  Reserved [this document]
- 0x80-0xFF Not Allocatable, corresponds to Composite tunnel types [this 
document]

The allocation policy for values 0x00 to 0x7A is IETF Review [RFC5226 
<https://tools.ietf.org/html/rfc5226>].
The range for experimental use is now 0x7B-0x7E, and value in this range 
are not to be assigned.
The status of 0x7F may only be changed through Standards Action [RFC5226 
<https://tools.ietf.org/html/rfc5226>].

----

Additionally to this section 8.1:
- the document header needs to specify "Updates: RFC7385" .
- the following can be added to the abstract (because reviewer often 
want to see in the abstract the explanation for why an RFC is updated): 
"This document makes use of the most significant bit of the scope 
governed by the IANA registry created by RFC7385, and hence updates that 
RFC accordingly."




> 6  Acknowledgement
>
>    We would like to thank Dennis Cai, Antoni Przygienda, and Jeffrey
>    Zhang for their valuable comments.
>
> 7  Security Considerations
>
>    Since this draft uses the EVPN constructs of [RFC7432] and [RFC7623],
>    the same security considerations in these drafts are also applicable
>    here. Furthermore, this draft provides additional security check by
>    allowing sites (or ACs) of an EVPN instance to be designated as
>    "Root" or "Leaf" and preventing any traffic exchange among "Leaf"
>    sites of that VPN through ingress filtering for known unicast traffic
>    and egress filtering for BUM traffic.
>
> 8  IANA Considerations
>
>    This document requests the allocation of value 5 in the "EVPN
>    Extended Community Sub-Types" registry defined in [RFC7153] and
>    modification of the registry as follow:

The text above should be reformulated to reflect the fact that IANA has 
already allocated the value: "IANA has allocated value 5 in the "EVPN 
Extended Community Sub-Types" registry defined in [RFC7153] as follow:"

>
>          SUB-TYPE VALUE     NAME                        Reference
>          0x05               E-TREE Extended Community   This document
>

Thanks,

-Thomas