Hi Thomas,
I have incorporated your new comments and generated the new text attached here.
Please review section 2.2 and let me know if there are any more comments.
Please refer below for the comment resolution explanation of some of the
comments.
Regards,
Ali
From: Thomas Morin <[email protected]<mailto:[email protected]>>
Organization: Orange
Date: Thursday, January 5, 2017 at 1:54 AM
To: Cisco Employee <[email protected]<mailto:[email protected]>>, Loa Andersson
<[email protected]<mailto:[email protected]>>, "George Swallow -T (swallow - MBO PARTNERS INC
at Cisco)" <[email protected]<mailto:[email protected]>>, Eric Rosen
<[email protected]<mailto:[email protected]>>, BESS
<[email protected]<mailto:[email protected]>>
Cc: Martin Vigoureux
<[email protected]<mailto:[email protected]>>
Subject: Re: shepherd review of draft-ietf-bess-evpn-etree
Hi Ali,
2016-12-19, Ali Sajassi (sajassi):
I have modified section 2.2 (copied below) to elaborate why coloring approach
for Leaf/Root MAC addresses is used in this draft. Also, the use of single RT
for this scenario is mentioned just as “MAY”. Please review the text below and
let me know if you still have questions/comments:
Thanks for providing text that goes in the right direction.
I still have a few comments below.
-Thomas
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 a Root AC or a Leaf AC
(but not both).
+---------+ +---------+
| 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, just like the previous scenario (in section 2.1),
two Route Targets (one for Root and another for Leaf) can be used.
However, the difference is that on a PE with both Root and Leaf ACs,
all remote MAC routes are imported and thus there needs to be a way
to differentiate remote MAC routes associated with Leaf ACs versus
the ones associated with Root ACs in order to apply the proper
ingress filtering.
In order to support such ingress filtering on the ingress PE with
both Leaf and Root ACs, one the following two approaches can be used:
reverting A and B would be more natural since solution B corresponds to the
starting point "what we had before this spec"
Done.
A) Color MAC addresses with Leaf (or Root) color before distributing
them in BGP to other PEs depending on whether it is learned on a Leaf
s/it is/they are/
Done.
AC (or a Root AC)
I think removing the parenthesis is needed for the 'whether' statement to parse.
Done.
B) Use two MAC-VRFs (two bridge tables per VLANs) - one for Root ACs
and another for Leaf ACs.
I think "(two bridge tables per VLANs)" is inexact: "two bridge tables per
VLAN if a given VLAN exists on the PE for both Leaf and Root ACs of a given
EVI" ?
That’s fine. Done!
Similarly, in the following paragraph, I think "per VLAN" should be replaced by
"per E-TREE EVI having both Root and Leaf ACs".
A single EVI can consist of many VLANs (in case of VLAN-aware bundle service),
so, “per VLAN” is right. However, to make it more exact as above, I’ll change
it to “per VLAN (when both Root and Leafs ACs exist for that VLAN) requires …”.
Maintaining two bridge tables per VLAN requires either two lookups be
performed per MAC address in either direction in case of a miss, or
duplicating many MAC addresses between the two bridge tables
belonging to the same VLAN (same E-TREE instance). The duplication of
MAC addresses are need for both locally learned and remotely learned
MAC addresses.
Since it is said above "Maintaining two bridge tables per VLAN requires either
two lookups [...] or duplicating many MAC addresses [...]", saying "The
duplication of MAC addresses is needed for [...]" is surprising, so I guess
the intent is rather "Unless two lookups are made, duplication of MAC addresses
would be needed for [...]".
That is correct. I’ll change it to the sentence that you suggested: “Unless two
lookups are made, …"
Locally learned MAC addresses from Leaf ACs need to be
duplicated onto Root bridge table and locally learned MAC addresses
from Root ACs need to be duplicated onto Leaf bridge table. Remotely
learned MAC addresses from Root ACs need to be copied onto both Root
and Leaf bridge tables.
Neither double lookups nor MAC duplications
are considered viable options; therefore, this draft recommends the
use of MAC address coloring for this scenario as detailed in section
3.1.
I think that this explanation is too elliptic compared to the strong ("not
viable") conclusion. As soon as we talk about implementation details, a more
detailed discussion is required on why, and under which assumptions, some
things are impossible -- there can be many different way to implement a
dataplane. Without explaining what "two lookups" exactly means in this context,
it's hard to follow why it would be required if duplicating MAC addresses is
not done, and why it is latter concluded as "not viable":
- doing multiple lookups is something that is far from being uncommon on router
platforms
- on software platforms the impact of doing multiple lookups can be reduced to
mostly zero (e.g. with OpenVSwitch that would only impact the first packets of
a flow)
- if the dataplane can leverage the colouring information to avoid doing two
lookups, then perhaps this hardware ability can be leveraged to support the two
MAC-VRFs approach with only one lookup (building one table, marking MAC
entries as Leaf entries if they were learned with routes carrying only the Leaf
RT?) --- don't misunderstand me: I'm not claiming that this works (I haven't
looked closely enough), but simply that the text provided is not sufficient to
exclude this kind of solution
The "duplicating MAC addresses" alternative is explained better, but still,
nothing is explained on why this is "not viable". It seems to be as something
rather belonging to the realm of "having a scalability impact", but even
looking in this respect we are not talking about a change of order of magnitude.
The non-viable conclusion was based on investigation that I did for micro-code
and ASIC based platforms; however, I see your point and I am para-phrasing the
sentence as follow to leave room for future investigation.
"In order to avoid two MAC-VRFs, this draft introduces the coloring option (B)
as detailed in section 3.1"
For this scenario, if for a given EVI, the vast majority of PEs will
have both Leaf and Root sites attached, even though they may start as
Root-only or Leaf-only PEs, then a single RT per EVI MAY be used in
order to alleviate additional configuration overhead associated with
"to alleviate additional configuration overhead associated with ..." -> "to
alleviate the configuration overhead associated with ..." ?
Done.
using two RTs per EVI at the expense of having unwanted MAC addresses
on the Leaf-only PEs.
From: Thomas Morin <[email protected]<mailto:[email protected]>>
Organization: Orange
Date: Thursday, December 15, 2016 at 4:12 AM
To: Cisco Employee <[email protected]<mailto:[email protected]>>, Loa Andersson
<[email protected]<mailto:[email protected]>>, "George Swallow -T (swallow - MBO PARTNERS INC
at Cisco)" <[email protected]<mailto:[email protected]>>, Eric Rosen
<[email protected]<mailto:[email protected]>>, BESS
<[email protected]<mailto:[email protected]>>
Cc: Martin Vigoureux
<[email protected]<mailto:[email protected]>>
Subject: Re: shepherd review of draft-ietf-bess-evpn-etree
Hi Ali,
2016-12-13, Ali Sajassi (sajassi):
2016-12-10, Ali Sajassi (sajassi):
Your suggestion regarding multiple MAC-VRFs per EVI for E-TREE, impacts lot
more sections than just section 2.2 for which you suggested some texts. It
drastically impacts section 3.1 (known unicast traffic), and it also impacts
section 3.2 (BUM traffic) and section 5.1.
Can you detail why ?
The understanding that leads me to this suggestion is that the
2-RT+split-horizon scenario in 2.1, then applied to Root/Leaf PE in a 2.2.1
would not require new procotol procedures nor changes in the text that as I
understand provides procedures for 2.2(.2) and 2.3.
2nd try. As my 1st response got truncated for some reason.
The reason that impacts more sections than just sec. 2, is that the proposed
2.2.1 would be an alternative option for section 3.1. In section 3.1, the
root/leaf indication for MAC addresses are done via flag-bit defined in section
5.1 and it only uses a single MAC-VRF (single bridge table per VLAN) per RFC
7432. If we go with two MAC-VRFs (e.g., two bridge tables) per VLAN, then that
is an alternative way of doing the same thing described in section 3.1. This
alternative way has big ramifications on the platform as it requires
duplicating MACs and managing multiple bridge tables per VLAN.
Since 2.1 and the proposed 2.2.1 do not require new protocol procedures (they
only require split-horizon locally in Leaf MAC-VRFs), if you state clearly that
the procedures in the document are here to address 2.2.2 and 2.3, then you
don't need to modify the content of the document after section 2 (more
exactly, you will need minor update like changing the current "This scheme
applies to all scenarios described in section 2." in section 3 into "This
scheme applies to scenarios described in 2.2.2 and 2.3".
The "big ramifications" above are then not about section 3, but just the
(platform specific-drawbacks) of 2.2.2 that we have already discussed and that
can be covered in 2.2.2.
Maybe what you really want is to allow for scenario 2.2 to operate with two RTs
which has the benefits of both 2.2.1 and 2.2.2 and non of the drawbacks. So,
maybe we can clarify the current text to make sure that this comes out clearly
– ie, a PE can have single MAC–VRF can have multiple RTs.
You could mention that, but for me the key things is:
- documenting the motivation for the new procedures
- not arbitrarily /restrict/ 2.2.2 to one RT (but why not document identified
drawbacks)
Furthermore, it creates a new paradigm for EVPN that was never intended for
because of creating two MAC-VRFs (and two bridge tables) for the same VLAN.
The "<new thing> created a new paradigm that <RFX xyz> was never intended for"
is a not generally valid, or sufficiently detailed, argument: if it was, then
you might go as far as challenging the whole E-Tree spec on the same kind
grounds (and many other new things).
So here is where it seems we have a gap to bridge: I still don't understand
what in RFC7432 describes an intention of "not supporting two MAC-VRFs for the
same VLAN".
I tried to explain the relationship between EVI, MAC-VRF, bridge table, and
VLAN in my previous email per RFC 7432. However, lets park this discussion for
time being as I think it is secondary.
Ok, feel free to revisit if you think that RFC7432 would preclude procedures
that end up being described in this draft
I think you agree that if we have a single solution that has all the benefits
of your proposed 2.2.1 and 2.2.2 and none of the drawbacks, it is much more
preferable with having two solutions each with its own advantages and draw
backs, right? If so, then existing text in 2.2 was intended to convey that.
However, we can clarify it further – e.g, make it clear that for PE with root &
leaf in the same EVI, we can use a single MAC-VRF with two RTs (one for leaf
and another for root).
As said above my key concern is having the document clearly spell out the
motivation for new specs.
If this implies documenting the fact that already existing procedure can be
used, but have drawbacks, then so be it ; there would be no point in hiding
that, right ?
The WG LC was completed on 3/29/16 and I am sure it is not your intention to
have major changes to the doc at this stage where multiple vendors have already
implemented the draft.
As you know, there are different stages at which people do reviews on a doc
after WGLC, an which may lead doc editors to introduce significant --editorial
or technical-- changes in a document. Sometimes that leads to documents going
back to the working group.
However my root intention as doc shepherd, of course, is not to propose a major
change, but merely to able to answer the standard question of the shepherd
review -- on the reviews done, on document readiness, and on the document
quality -- in a way as positive and sincere as possible. In particular
questions (3) (4) and (6).
So, hopefully the answers to these three questions are now clear. I believe
your main concern is to ensure that we can apply two-RT approach of sec. 2.1
to sec. 2.2 (and we can still do and still have a single MAC-VRF)
See above.
This draft talks about two kinds of traffic filtering: a) ingress filtering for
known unicast and b) egress filtering for BUM traffic. What you are suggesting
is an alternate mechanism for ingress filtering.
(well I'm not suggesting the mechanism itself --which section 2.1 already
does-- but simply to document that it can still apply without the constraint of
avoiding the presence of a Root MAC-VRF and a Leaf MAC-VRF on a same PE)
Although having multiple VRFs (and forwarding tables) are fine for IP-VPNs
because the unknown traffic is always dropped, multiple VRFs for the same VLAN
is not OK for L2 traffic because of flooding of unknown traffic. That’s why in
section 6 of RFC 7432, for all service interface types, the draft talks about a
single MAC-VRF per EVI per PE and in case of VLAN-aware mode, multiple VLANs
per MAC-VRF but only a single bridge table per VLAN. In other words, the bottom
line is that there can only be a single bridge table per VLAN in order to avoid
unnecessary flooding.
When you have two MAC-VRFs per VLAN (one for root ACs and another for Leaf
ACs), then you either need to duplicate lots of MAC addresses between these two
VRFs, or do lookup on both of these VRFs. Either ways this is not a good option
relative to keeping a single VRF table for both root and leaf sites and just
have a single-bit indication on whether a MAC is associated with root or leaf
(as currently described approach in the draft). I
In the above, it seems you agree that it can work, and you are able to offer
reasons why it is not the preferred option, then why not just document that it
can work and provides these reasons as the motivations that lead to proposing a
new specs ?
Sure, I can do that. [...]
Ok.
I'll be happy to review a new revision and hopefully post the shepherd review.
Thanks,
-Thomas
(it seems you have an unfinished last sentence: "I [...]" )
(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)
That’s not possible because per definition of an EVI, there is only a single
MAC-VRF per EVI for a PE.
Where can I read such a definition ? (the Terminology section in RFC7432 does
not say that, unless I'm missing something).
And that seems a completely arbitrary restriction.
(just thinking that a given PE device can be split in two logical devices show
that it can work)
Section 6 of RFC7432 where it gives definitions for different service interface
types, it specifies the relationship between MAC-VRF and VLAN (bridge table)
and how many MAC-VRF (and bridge tables) can be per EVI.
This section of RFC7434 discusses many different things for the different
variants.
Can you provide a specific pointer about "how many MAC-VRFs can be per EVI" ?
Ali> Section 6 of RFC7432 spells out the relationship between EVI, MAC-VRF, and
bridge tables for all service interfaces very clearly.
In all service interfaces, the RFC says there is one MAC-VRF per EVI on a given
PE.
Now, if the service interface is “vlan-aware”, then there are several bridge
tables for that single MAC-VRF – ie, one bridge table per VLAN. In all service
interfaces, you can ONLY have one bridge table per VLAN.
This answer is everything but a specific pointer.
If Section 6 of RFC7432 says all this very clearly, I guess it should be
possible to extract quotes about "there is one MAC-VRF per EVI on a given PE",
right ?
In bridging world, there can only be a single bridge table per VLAN in a device.
I still don't find here anything that would preclude having, on a given PE, for
a given E-TREE EVI, one Leaves MAC-VRF and one Roots MAC-VRF: can't these two
MAC-VRFs use different internal VLANs (with translation if the external VLANs
are constrained).
Ali> Lets assume we are using vlan-based service and thus there is only a
single bridge table per MAC-VRF, then what you are suggesting is two use two
MAC-VRFs (two bridge tables) for the same EVI (same VLAN). This results in some
duplications of MAC addresses and would only work if flooding is disabled (more
on this later).
"results in some duplications of MAC" is perhaps a drawback, but nothing like
"just does not work" ?
"would only work if flooding is disabled": why ? (you wrote "(more on this
later)" but I couldn't identify anything recent from you in the rest of the
email below)
>From an helicopter view, I can't see what fundamentally would become
>problematic between "two MAC-VRFs on two distinct PEs" and the same "two
>MAC-VRFs on a same PEs", at worse it is as efficient or as inefficient as
>having them on separate PEs (think logical router without anykind of dataplane
>optimisation), and we can't exclude that the PE could have local
>implementation details to do better than that.
Besides, I don’t understand what good does it do to have two MAC-VRFs on the
same PE (one for Leafs and another for Roots)
Well, the "what is good for" is pretty simple: it means you can have, just by
tailoring the import/export policies like in 2.1, something as useful as the
scenario in 2.2.
There can only be a single bridge table per VLAN. Now even if you add some kind
of logic to form two logical PEs in single physical PE, you end up replicating
all the MAC addresses associated with the root sites in two bridge tables.
Your point above certainly does not sound to me as "it can't be done": some may
think that the above is an acceptable cost, some others may find ways to make
this "replication" with a low overhead, on some platforms the cost may be
negligible, etc.
because Leafs and Roots need to talk to each other and thus we want them to be
in the same MAC-VRF.
The fact that Leafs and Roots need to talk to each other does not mean that
they *have* to be in the same MAC-VRF, you can rely on the local MPLS dataplane
inside the PE to carry the traffic between Roots and Leaves can be passed
between a Leaf MAC-VRF and a Root MAC-VRF (and you can possibly implement a
shortcut not involving MPLS encap/decap).
Anything is possible but at what cost.
You know, for cost it is not always obvious to reach conclusions that are true
for all implementations and all targets.
The current proposal is very efficient in terms of forwarding path as well as
control plane.
Sure, but what I question is not the new solution but the lack of discussion on
why using the existing specs was not considered good enough.
I think that my concern of clearly explaining the scenarios and motivations for
this new spec could be addressed by splitting section 2.2 into a 2.2.1
describing the approach from 2.1 and its possible drawbacks, and a 2.2.2 having
essentially the content of current section 2.2.
Here is a proposal:
2.2 Scenario 2: Leaf of Root site(s) per AC
In these scenarii, 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 Root(s)
or Leaf(s) (but not both).
2.2.1 Scenario 2a: Leaf OR Root site(s) per AC, separate Leaf/Root MAC-VRFs
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | | | |MAC+--+---ES2/AC1--+CE2|
+---+ (Leaf) | |MAC| | | MPLS | | |VRF| | (Leaf) +---+
| |VRF| | | /IP | | '---' |
| | | | | | | .---. |
| | | | | | | |MAC| | +---+
| | | | | | | |VRF+--+---ES2/AC2--+CE3|
| +---+ | +------+ | +---+ | (Root) +---+
+---------+ +---------+
Figure 2: Scenario 2a
In this scenario, the RT constraint procedures described in section 2.1 could
also be used. The feasibility and efficiency of this approach depends on
platforms specifics.
This approach will lead toduplication of a large proportion of MAC addresses
on
PEs having both Leaf and Root sites, and is hence considered less suitable
for
deployment contexts where the vast majority of PEs are likely to ultimately
have both Leaf and Root sites attached to them.
2.2.2 Scenario 2b: Leaf OR Root site(s) per AC, single MAC-VRF
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----ES1----+--+ | | | | | | +--+---ES2/AC1--+CE2|
+---+ (Leaf) | |MAC| | | MPLS | | |MAC| | (Leaf) +---+
| |VRF| | | /IP | | |VRF| |
| | | | | | | | | | +---+
| | | | | | | | +--+---ES2/AC2--+CE3|
| +---+ | +------+ | +---+ | (Root) +---+
+---------+ +---------+
Figure 2: Scenario 2b
This scenario will alleviate keys drawbacks from Scenario 2a, in particular
by avoiding duplication of MAC addresses on Leaf/Root PEs and avoiding the
operational overhead of managing more than one RT.
This approach comes at the expense of having routes for unneeded MAC
addresses
on Leaf-only PEs, and is hence considered less suitable for deployment
contexts
where the vast majority of PEs would remain Leaf-only. Unlike Scenario 1
and Scenario 2a, this scenario requires additional procedures
provided in this document.
(And this last sentence should be added to section 2.3 as well)
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.
OK, I changed “majority” to “vast majority” :-)
My point was not to nit pick on "majority", but was that you should explain why
you recommend that.
As the text currently reads, the cost of the recommendation can be identified:
having useless routes on the fraction of PEs having only Leaves.
But the gain brought by the recommendation is not even mentioned, not to say
explained.
Hence: why ?
(Why is it a useful tradeoff to have useless routes on some, even if only one,
PE ?)
Changed the last sentence from:
"then it is recommended to use a single RT per EVI and avoid additional
configuration and operational overhead.”
To
"then it is recommended to use a single RT per EVI and avoid additional
configuration and operational overhead
at the expense of having unwanted MAC addresses on the Leaf PEs."
Ok. I adapted and incorporated this addition into my proposed text splitting
2.2 into a 2.2.1 and a 2.2.2.
Best,
-Thomas
BESS Workgroup A. Sajassi, Ed.
INTERNET-DRAFT S. Salam
Intended Status: Standards Track Cisco
Updates: RFC7385 J. Drake
Juniper
J. Uttaro
ATT
S. Boutros
VMware
J. Rabadan
Nokia
Expires: May 20, 2017 December 20, 2016
E-TREE Support in EVPN & PBB-EVPN
draft-ietf-bess-evpn-etree-08
Abstract
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). A solution
framework for supporting this service in MPLS networks is proposed in
and RFC called "A Framework for E-Tree Service over MPLS Network".
This document discusses how those functional requirements can be
easily met with (PBB-)EVPN and how (PBB-)EVPN offers a more efficient
implementation of these functions. 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.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
Sajassi et al. Expires May 20, 2017 [Page 1]
INTERNET DRAFT E-TREE Support in EVPN & PBB-EVPN December 20, 2016
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2 E-Tree Scenarios and EVPN / PBB-EVPN Support . . . . . . . . . 4
2.1 Scenario 1: Leaf OR Root site(s) per PE . . . . . . . . . . 4
2.2 Scenario 2: Leaf OR Root site(s) per AC . . . . . . . . . . 5
2.3 Scenario 3: Leaf OR Root site(s) per MAC . . . . . . . . . . 7
3 Operation for EVPN . . . . . . . . . . . . . . . . . . . . . . . 7
3.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 7
3.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2.1 BUM traffic originated from a single-homed site on a
leaf AC . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.2 BUM traffic originated from a single-homed site on a
root AC . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.3 BUM traffic originated from a multi-homed site on a
leaf AC . . . . . . . . . . . . . . . . . . . . . . . . 10
3.2.4 BUM traffic originated from a multi-homed site on a
root AC . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 E-TREE Traffic Flows for EVPN . . . . . . . . . . . . . . . 11
3.3.1 E-Tree with MAC Learning . . . . . . . . . . . . . . . . 11
3.3.2 E-Tree without MAC Learning . . . . . . . . . . . . . . 12
4 Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . . . 12
4.1 Known Unicast Traffic . . . . . . . . . . . . . . . . . . . 13
4.2 BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . . 13
Sajassi et al. Expires May 20, 2017 [Page 2]
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4.3 E-Tree without MAC Learning . . . . . . . . . . . . . . . . 14
5 BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 E-TREE Extended Community . . . . . . . . . . . . . . . . . 14
5.2 PMSI Tunnel Attribute . . . . . . . . . . . . . . . . . . . 15
6 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . 16
7 Security Considerations . . . . . . . . . . . . . . . . . . . . 16
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 16
8.1 Considerations for PMSI Tunnel Types . . . . . . . . . . . . 16
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1 Normative References . . . . . . . . . . . . . . . . . . . 17
9.2 Informative References . . . . . . . . . . . . . . . . . . 17
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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1 Introduction
The Metro Ethernet Forum (MEF) has defined a rooted-multipoint
Ethernet service known as Ethernet Tree (E-Tree). In an E-Tree
service, endpoints are labeled as either Root or Leaf sites. Root
sites can communicate with all other sites. Leaf sites can
communicate with Root sites but not with other Leaf sites.
[RFC7387] proposes the solution framework for supporting E-Tree
service in MPLS networks. The document identifies the functional
components of the overall solution to emulate E-Tree services in
addition to Ethernet LAN (E-LAN) services on an existing MPLS
network.
[RFC7432] is a solution for multipoint L2VPN services, with advanced
multi-homing capabilities, using BGP for distributing customer/client
MAC address reach-ability information over the MPLS/IP network.
[RFC7623] combines the functionality of EVPN with [802.1ah] Provider
Backbone Bridging for MAC address scalability.
This document discusses how the functional requirements for E-Tree
service can be easily met with (PBB-)EVPN and how (PBB-)EVPN offers a
more efficient implementation of these functions.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [KEYWORDS].
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
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concurrently. In other words, a given EVI on a PE is either
associated with root(s) or leaf(s). The PE may have both Root and
Leaf 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, using tailored BGP Route Target (RT) import/export
policies among the PEs belonging to the same EVI, can be used to
restrict the communications among Leaf PEs. To restrict the
communications among Leaf sites connected to the same PE and
belonging to the same EVI, split-horizon filtering is used to block
traffic from one Leaf interface to another Leaf interface of a given
E-TREE 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.
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 a Root AC or a Leaf AC
(but not both).
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+---------+ +---------+
| 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, just like the previous scenario (in section 2.1),
two Route Targets (one for Root and another for Leaf) can be used.
However, the difference is that on a PE with both Root and Leaf ACs,
all remote MAC routes are imported and thus there needs to be a way
to differentiate remote MAC routes associated with Leaf ACs versus
the ones associated with Root ACs in order to apply the proper
ingress filtering.
In order to support such ingress filtering on the ingress PE with
both Leaf and Root ACs, one the following two approaches can be used:
A) To use two MAC-VRFs (two bridge tables per VLANs if a given VLAN
exists on the PE for both Leaf and Root ACs of an EVI) - one for Root
ACs and another for Leaf ACs.
B) To color MAC addresses with Leaf or Root color before distributing
them in BGP to other PEs depending on whether they are learned on a
Leaf AC or a Root AC.
Maintaining two bridge tables per VLAN (when both Leaf and Root ACs
exists for that VLAN) requires either two lookups be performed per
MAC address in either direction in case of a miss, or duplicating
many MAC addresses between the two bridge tables belonging to the
same VLAN (same E-TREE instance). Unless two lookups are made,
duplication of MAC addresses would be needed for both locally learned
and remotely learned MAC addresses. Locally learned MAC addresses
from Leaf ACs need to be duplicated onto Root bridge table and
locally learned MAC addresses from Root ACs need to be duplicated
onto Leaf bridge table. Remotely learned MAC addresses from Root ACs
need to be copied onto both Root and Leaf bridge tables. In order to
avoid two MAC-VRFs, this draft introduces the coloring option (B) as
detailed in section 3.1.
For this scenario, if for a given EVI, the vast majority of PEs will
have both Leaf and Root sites attached, even though they may start as
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Root-only or Leaf-only PEs, then a single RT per EVI MAY be used in
order to alleviate the configuration overhead associated with using
two RTs per EVI at the expense of having unwanted MAC addresses on
the Leaf-only PEs.
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 single 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
identified is on a per MAC address. This scenario is considered in
this draft for EVPN service with only known unicast traffic because
the DF filtering per [RFC7432] would not be compatible with the
required egress filtering - i.e., BUM traffic is not supported in
this scenario and it is dropped by the ingress PE.
+---------+ +---------+
| 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
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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/IP Advertisement route, then it notifies the operator and ignore
the leaf indication on the Ethernet A-D per EVI 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. 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.
In situation where MAC moves are allowed among Leaf and Root sites
(e.g., non-static MAC), PEs can receive multiple MAC/IP
advertisements routes for the same MAC address with different
Leaf/Root indications (and possibly different ESIs for multi-homing
scenarios). In such situations, MAC mobility procedures take
precedence to first identify the location of the MAC before
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associating that MAC with a Root or a Leaf site.
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
This specification does not provide support for filtering BUM traffic
on the ingress PE because it is not possible to perform filtering of
BUM traffic on the ingress PE, as is the case with known unicast
described above, due to the multi-destination nature of BUM traffic.
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].
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. This split-horizon function applies to BUM
traffic as well as known-unicast traffic.
There are four scenarios to consider as follows. In all these
scenarios, the ingress PE imposes the right MPLS label associated
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 label 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 AC identifier for that segment
(e.g., Ethernet Tag of the frame for 802.1Q frames). Other mechanisms
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for identifying root or leaf (e.g., on a per MAC address basis) 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 label 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
the same ES could have different root/leaf designation (some being
roots and some being leafs), the same AC (e.g., 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 or broadcast packet is originated
from a leaf 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
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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(s) with Root sites performs MAC learning in the
data-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
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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
route is used to support BUM traffic.
The fields of this 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
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(VLANs) on the same ES could have different root/leaf designation
(some being roots and some being leafs), 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 for BUM traffic), it updates its egress filtering (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 its B-MAC list used for egress
filtering - i.e., to block traffic from that B-MAC address.
- Otherwise, the B-MAC filtering list is not updated.
When the egress PE receives the packet, it examines the B-MAC source
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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.
Just as in section 3.2, 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. This split-horizon
function applies to BUM traffic as well as known-unicast traffic.
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:
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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:
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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.
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.
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
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
8.1 Considerations for PMSI Tunnel Types
The "P-Multicast Service Interface Tunnel (PMSI Tunnel) Tunnel Types"
registry in the "Border Gateway Protocol (BGP) Parameters" registry
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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]. 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].
9 References
9.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7432] Sajassi et al., "BGP MPLS Based Ethernet VPN", February,
2015.
[RFC7623] Sajassi et al., "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", September, 2015.
[RFC7385] Andersson et al., "IANA Registry for P-Multicast
Service Interface (PMSI) Tunnel Type Code Points",
October, 2014.
[RFC7153] Rosen et al., "IANA Registries for BGP Extended
Communities", March, 2014.
[RFC6514] Aggarwal et al., "BGP Encodings and Procedures
for Multicast in MPLS/BGP IP VPNs", February, 2012.
9.2 Informative References
[RFC7387] Key et al., "A Framework for E-Tree Service over MPLS
Network", October 2014.
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[RFC4360] S. Sangli et al, "BGP Extended Communities Attribute",
February, 2006.
Contributors
In addition to the authors listed on the front page, the following
co-authors have also contributed to this document:
Wim Henderickx
Nokia
Aldrin Isaac
Wen Lin
Juniper
Authors' Addresses
Ali Sajassi
Cisco
Email: [email protected]
Samer Salam
Cisco
Email: [email protected]
John Drake
Juniper
Email: [email protected]
Jim Uttaro
AT&T
Email: [email protected]
Sami Boutros
VMware
Email: [email protected]
Jorge Rabadan
Nokia
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Email: [email protected]
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