RFC 8317
Ethernet-Tree (E-Tree) Support in Ethernet VPN (EVPN) and Provider Backbone Bridging EVPN (PBB-EVPN)
RFC 8317: Ethernet-Tree (E-Tree) Support in Ethernet VPN (EVPN) and Provider Backbone Bridging EVPN (PBB-EVPN) 🎀
okay bestie, first the paperwork 📋 This is RFC 8317, a Standards Track document from the IETF, dated January 2018 (ISSN 2070-1721). The editor is A. Sajassi, Ed. 💅 The other authors are S. Salam (Cisco), J. Drake (Juniper), J. Uttaro (ATT), S. Boutros (VMware), and J. Rabadan (Nokia). The only thing it updates is RFC 7385 🦋 and the title block doesn't list anything it obsoletes.
Abstract
okay so the MEF Forum (MEF) defined a rooted-multipoint Ethernet service called Ethernet-Tree (E-Tree) 🌳 RFC 7387, "A Framework for Ethernet-Tree (E-Tree) Service over a Multiprotocol Label Switching (MPLS) Network", gives a solution framework for running this service over MPLS networks ✨ This document shows how those functional requirements can be met with a solution based on RFC 7432, "BGP MPLS Based Ethernet VPN (EVPN)", plus some extensions. It also explains how this solution can be a more efficient way to do these functions than RFC 7796, "Ethernet-Tree (E-Tree) Support in Virtual Private LAN Service (VPLS)" 💖
It's giving precision here: this document uses the most significant bit of the Tunnel Type field (in the P-Multicast Service Interface (PMSI) Tunnel attribute) that is governed by the IANA registry created by RFC 7385. So it updates RFC 7385 accordingly 🎀
Status of This Memo
This is an Internet Standards Track document. 🌸
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Info about the current status of this document, any errata, and how to give feedback is at https://www.rfc-editor.org/info/rfc8317 🦋
Copyright Notice
Copyright (c) 2018 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 (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, since 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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Specification of Requirements . . . . . . . . . . . . . . 5
2.2. Terms and Abbreviations . . . . . . . . . . . . . . . . . 5
3. E-Tree Scenarios . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Scenario 1: Leaf or Root Site(s) per PE . . . . . . . . . 6
3.2. Scenario 2: Leaf or Root Site(s) per AC . . . . . . . . . 7
3.3. Scenario 3: Leaf or Root Site(s) per MAC Address . . . . 8
4. Operation for EVPN . . . . . . . . . . . . . . . . . . . . . 9
4.1. Known Unicast Traffic . . . . . . . . . . . . . . . . . . 9
4.2. BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.1. BUM Traffic Originated from a Single-Homed Site on a
Leaf AC . . . . . . . . . . . . . . . . . . . . . . . 11
4.2.2. BUM Traffic Originated from a Single-Homed Site on a
Root AC . . . . . . . . . . . . . . . . . . . . . . . 11
4.2.3. BUM Traffic Originated from a Multihomed Site on a
Leaf AC . . . . . . . . . . . . . . . . . . . . . . . 12
4.2.4. BUM Traffic Originated from a Multihomed Site on a
Root AC . . . . . . . . . . . . . . . . . . . . . . . 12
4.3. E-Tree Traffic Flows for EVPN . . . . . . . . . . . . . . 12
4.3.1. E-Tree with MAC Learning . . . . . . . . . . . . . . 13
4.3.2. E-Tree without MAC Learning . . . . . . . . . . . . . 14
5. Operation for PBB-EVPN . . . . . . . . . . . . . . . . . . . 14
5.1. Known Unicast Traffic . . . . . . . . . . . . . . . . . . 15
5.2. BUM Traffic . . . . . . . . . . . . . . . . . . . . . . . 15
5.3. E-Tree without MAC Learning . . . . . . . . . . . . . . . 16
6. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. E-Tree Extended Community . . . . . . . . . . . . . . . . 16
6.2. PMSI Tunnel Attribute . . . . . . . . . . . . . . . . . . 17
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
8.1. Considerations for PMSI Tunnel Types . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Multiple Bridge Tables per E-Tree Service Instance . 22
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 231. Introduction ✨
okay so the MEF Forum (MEF) defined a rooted-multipoint Ethernet service called Ethernet-Tree (E-Tree) [MEF6.1]. In an E-Tree service, a customer site (usually represented by an Attachment Circuit (AC), e.g., an 802.1Q VLAN tag [IEEE.802.1Q]) is labeled as either a Root or a Leaf site. A customer site can also be represented by a Media Access Control (MAC) address along with a VLAN tag. Root sites can communicate with all other customer sites (both Root and Leaf sites). Leaf sites can communicate with Root sites, but not with other Leaf sites. Unless explicitly mentioned otherwise, a site is always represented by an AC in this document 🎀
RFC 7387 describes a solution framework for E-Tree service in MPLS networks 🦋 This document identifies the functional components of an overall solution to emulate E-Tree services in MPLS networks. It also supplements the multipoint-to-multipoint Ethernet LAN (E-LAN) services specified in [RFC7432] and [RFC7623].
[RFC7432] defines EVPN, a solution for multipoint Layer 2 Virtual Private Network (L2VPN) services with advanced multihoming capabilities. It uses BGP to distribute customer/client MAC address reachability information over the MPLS/IP network 💅 [RFC7623] combines the functionality of EVPN with [IEEE.802.1ah] Provider Backbone Bridging (PBB) for MAC address scalability 🧚
This document discusses how the functional requirements for E-Tree service can be met with a solution based on EVPN [RFC7432] and PBB-EVPN [RFC7623], with some extensions to their procedures and BGP attributes. A solution based on PBB-EVPN or EVPN can offer a more efficient implementation of these functions than [RFC7796], "Ethernet-Tree (E-Tree) Support in Virtual Private LAN Service (VPLS)". 🔥 The efficiency comes from doing filtering of unicast traffic at the ingress Provider Edge (PE) nodes. The alternative is egress filtering, where the traffic gets sent through the network and then filtered and discarded at the egress PE nodes 🙈 The details of this ingress filtering are described in Section 4.1. Since this document specifies a solution based on [RFC7432], knowing that document is a prerequisite 📚
This document makes use of the most significant bit of the Tunnel Type field (in the PMSI Tunnel attribute) governed by the IANA registry created by [RFC7385]. Hence, it updates [RFC7385] accordingly. Section 3 discusses E-Tree scenarios. Sections 4 and 5 describe E-Tree solutions for EVPN and PBB-EVPN (respectively). Section 6 covers BGP encoding for E-Tree solutions 🌈
2. Terminology 💜
2.1. Specification of Requirements
Here's the serious bit, so read carefully 👀 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
2.2. Terms and Abbreviations 🍓
- Broadcast Domain: In a bridged network, the broadcast domain corresponds to a Virtual LAN (VLAN). A VLAN is typically represented by a single VLAN ID (VID), but it can be represented by several VIDs where Shared VLAN Learning (SVL) is used per [IEEE.802.1ah].
- Bridge Table: An instantiation of a broadcast domain on a MAC-VRF.
- CE: A Customer Edge device, e.g., a host, router, or switch.
- EVI: An EVPN Instance spanning the Provider Edge (PE) devices participating in that EVPN.
- MAC-VRF: A Virtual Routing and Forwarding table for Media Access Control (MAC) addresses on a PE.
- ES: When a customer site (device or network) is connected to one or more PEs via a set of Ethernet links, that set of links is referred to as an "Ethernet Segment". 🔗
- ESI: An Ethernet Segment Identifier is a unique non-zero identifier that identifies an ES.
- Ethernet Tag: An Ethernet Tag identifies a particular broadcast domain, e.g., a VLAN. An EVPN instance consists of one or more broadcast domains.
- P2MP: Point-to-Multipoint.
- PE: Provider Edge device.
3. E-Tree Scenarios 🌷
This document sorts E-Tree scenarios into three categories, depending on the nature of the Root/Leaf site association:
- Scenario 1: either Leaf or Root site(s) per PE;
- Scenario 2: either Leaf or Root site(s) per Attachment Circuit (AC); or,
- Scenario 3: either Leaf or Root site(s) per MAC address.
3.1. Scenario 1: Leaf or Root Site(s) per PE ✨
okay so bestie, in this scenario a PE can get traffic from Root ACs or Leaf ACs for a given MAC-VRF/bridge table, but NOT both 🙅♀️ 💅. Put another way, a given EVI on a Provider Edge (PE) device is either tied to Root(s) or Leaf(s). A PE is allowed to have both Root and Leaf ACs, just for different EVIs 🦋.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+---AC1----+--+ | | | MPLS | | | +--+----AC2-----+CE2|
+---+ (Root) | |MAC| | | /IP | | |MAC| | (Leaf) +---+
| |VRF| | | | | |VRF| |
| | | | | | | | | | +---+
| | | | | | | | +--+----AC3-----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 1: Scenario 1So here's the tea ☕ 💖. Tailored BGP Route Target (RT) import/export policies among the PEs in the same EVI can be used to stop Leaf PEs from talking to each other 🙈. And to stop Leaf ACs on the same PE (same EVI) from chatting, split-horizon filtering blocks traffic from one Leaf AC to another Leaf AC on a MAC-VRF for a given E-Tree EVI 🚫. The whole point of this topology constraint is to avoid PEs with only Leaf sites importing and processing BGP MAC routes from each other, lowkey the main goal 🎀.
To make that work in EVPN, every EVI gets two BGP RTs 👯♀️: one for the Root sites (Root ACs) and one for the Leaf sites (Leaf ACs). Per EVI, every PE exports just the single RT that matches its type of site(s) 📤. A PE with Root site(s) imports BOTH the Root and Leaf RTs 🌸, whereas a PE with only Leaf site(s) imports just the Root RT 🧚.
If you'd rather use only a single RT per EVI (like E-LAN services in [RFC7432]) for this scenario, then approach B in Scenario 2 (down below) is the move 🔥.
3.2. Scenario 2: Leaf or Root Site(s) per AC 💜
in this one, a PE can get traffic from both Root ACs and Leaf ACs for a given EVI 🌈. So basically a given EVI on a PE can be associated with both Root(s) and Leaf(s) ✨.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----AC1----+--+ | | | | | | +--+---AC2--+CE2|
+---+ (Leaf) | |MAC| | | MPLS | | |MAC| | (Leaf) +---+
| |VRF| | | /IP | | |VRF| |
| | | | | | | | | | +---+
| | | | | | | | +--+---AC3--+CE3|
| +---+ | +------+ | +---+ | (Root) +---+
+---------+ +---------+
Figure 2: Scenario 2Same deal as Scenario 1 (see Section 3.1) 💅: two RTs, one for Root and one for Leaf, can be used. The plot twist 😭 is that on a PE with both Root and Leaf ACs, ALL remote MAC routes get imported. So to do the proper ingress filtering, there has to be a way to tell apart remote MAC routes tied to Leaf ACs from the ones tied to Root ACs 🕵️♀️.
So to figure out whether a destination MAC belongs to a Leaf or Root AC (and make ingress filtering work on a PE with both kinds of AC), MAC addresses need to be colored with a Root or Leaf-Indication before they're advertised to other PEs 🎨. There are two ways to do that coloring:
- (A) always use two RTs (one to designate the Leaf RT and another for the Root RT), or
- (B) allow a single RT per EVI, just like [RFC7432], and color MAC addresses with a "color" flag in a new extended community, as detailed in Section 6.1 🦋.
Approach A would need the same data-plane enhancements as approach B if the MAC-VRF and bridge tables used per VLAN are to stay consistent with Section 6 of [RFC7432] 🧩. You could dodge those data-plane enhancements for approach A by using multiple bridge tables per VLAN, but that has major drawbacks (see Appendix A), so it is not recommended 🙅♀️.
Since A and B would need the same data-plane enhancements anyway, approach B is the one picked here 👑. It keeps RT usage consistent with baseline EVPN [RFC7432] and is more general 🌟. Also worth noting 📝: if you want RT constraints to stop MAC advertisements for a Leaf AC from reaching PEs with only Leaf ACs, you can still use two RTs (one for Root and one for Leaf) with approach B 💖. But in that case the Leaf/Root RTs are only used to constrain MAC advertisements, NOT to color the MAC routes for ingress filtering. (In approach B, the coloring is always done via the new extended community 🎀.)
If, for a given EVI, a significant number of PEs have both Leaf and Root sites attached (even if they started out as Root-only or Leaf-only PEs 🌱), then a single RT per EVI SHOULD be used 🫶. The reason is to cut down on the config overhead of using two RTs per EVI, at the cost of having some unwanted MAC addresses on the Leaf-only PEs 😬.
3.3. Scenario 3: Leaf or Root Site(s) per MAC Address 🦋
in this scenario, a customer Root or Leaf site is represented by a MAC address on an AC, and a PE may receive traffic from both Root and Leaf sites on that AC for an EVI 🫣. This one isn't covered in either [RFC7387] or [MEF6.1] 📚, but this document covers it anyway for the sake of completeness 🌸. Since one AC carries traffic from both Root and Leaf sites, Root or Leaf sites get identified on a per-MAC-address basis 🔍. This scenario only considers EVPN service with known unicast traffic, because Designated Forwarder (DF) filtering per [RFC7432] wouldn't be compatible with the required egress filtering 🙃. So BUM traffic (Broadcast, Unknown Unicast, and Multicast) is NOT supported here, and the ingress PE drops it 🗑️.
For this scenario, approach B in Scenario 2 is used so service providers can get single RT usage 👑.
+---------+ +---------+
| PE1 | | PE2 |
+---+ | +---+ | +------+ | +---+ | +---+
|CE1+-----AC1----+--+ | | | | | | +--+-----AC2----+CE2|
+---+ (Root) | | E | | | MPLS | | | E | | (Leaf/Root)+---+
| | V | | | /IP | | | V | |
| | I | | | | | | I | | +---+
| | | | | | | | +--+-----AC3----+CE3|
| +---+ | +------+ | +---+ | (Leaf) +---+
+---------+ +---------+
Figure 3: Scenario 3In conclusion 🎀, approach B in Scenario 2 is the RECOMMENDED approach across all three scenarios above, and the solution for it is detailed in the following sections 💜✨.
4. Operation for EVPN 🌈
[RFC7432] defines the Ethernet Segment Identifier (ESI) MPLS label used for split-horizon filtering of BUM traffic at the egress PE 🧚. That egress filtering can be leveraged to provide E-Tree services, as we'll see shortly for BUM traffic 🦋. For known unicast traffic, you need extra extensions to [RFC7432] (namely a new BGP extended community for Leaf-Indication, described in Section 6.1) 🔧 so ingress filtering can happen, as detailed in the following sections 💅.
4.1. Known Unicast Traffic 💖
In EVPN, MAC learning happens in the control plane through advertisement of BGP routes 📡. Because of that, the filtering an E-Tree service needs for known unicast traffic can be done at the ingress PE ✨. That's super efficient, since it avoids sending known unicast traffic over the MPLS/IP core just to get filtered at the egress PE, which is what traditional E-Tree solutions do (i.e., E-Tree for VPLS [RFC7796]) 🙄.
To provide that 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 🚨. It does this by advertising a Leaf-Indication flag (via an extended community) along with each of its MAC/IP Advertisement routes learned from a Leaf site 🏷️. No flag means the MAC address is associated with a Root site 🌟. This scheme applies to all scenarios in Section 3 💜.
Tagging MAC addresses with a Leaf-Indication lets remote PEs do ingress filtering for known unicast traffic 🎯. On the ingress PE, the MAC destination address lookup yields (along with the forwarding adjacency) a flag showing whether or not the target MAC is associated with a Leaf site 🔎. The ingress PE cross-checks that flag against the status of the originating AC, and if both are Leafs, the packet is NOT forwarded 🚫.
Now, if MAC moves are allowed among Leaf and Root sites (e.g., non-static MAC) 🏃♀️, PEs can get multiple MAC/IP Advertisement routes for the same MAC address with different Root or Leaf-Indications (and maybe different ESIs for multihoming scenarios) 🌀. In that case, MAC mobility procedures (see Section 15 of [RFC7432]) take priority, so the MAC's location gets figured out first, and only then is it associated with a Root or Leaf site 🧭.
To support all this ingress filtering, a new E-Tree extended community with a Leaf-Indication flag is introduced (see Section 6.1) 🎀. This new extended community MUST be advertised with MAC/IP Advertisement routes learned from a Leaf site 💅. Apart from MAC/IP Advertisement routes, no other EVPN routes need to carry this new extended community for known unicast traffic purposes 🫶.
4.2. BUM Traffic 🎀
okay so BUM traffic (Broadcast, Unknown Unicast, and Multicast, iykyk 🙈) is lowkey the most chaotic kind of traffic because it goes to multiple destinations at once. This specification does not filter BUM traffic on the ingress PE, since you literally cannot filter a multidestination packet there. So the whole solution relies on egress filtering 💅. To pull that off, MPLS-encapsulated frames MUST be tagged with a marker saying whether they came from a Leaf AC, using a Leaf label from Section 6.1. That Leaf label lets the disposition PE (like the egress PE) do the egress filtering in the data plane, kind of like the ESI label in [RFC7432] 🦋. The Leaf label is allocated per PE (so it's independent of ESI and EVI), as you'll see in the sections below ✨.
The Leaf label can be upstream assigned for a Point-to-Multipoint (P2MP) Label Switched Path (LSP), or downstream assigned for Ingress Replication tunnels. The big difference is that with downstream-assigned Leaf labels, not every egress PE has to receive the label in MPLS-encapsulated BUM packets. That's the same vibe as the ESI label for Ingress Replication procedures in [RFC7432] 🌸.
On the ingress PE, all Leaf ACs for a given bridge domain go into a single split-horizon group. This stops intra-PE forwarding among Leaf ACs, and it applies to BUM traffic and known unicast traffic alike 🧚.
There are four scenarios to look at. In every one of them, the ingress PE imposes the correct MPLS label tied to the originating Ethernet Segment (ES), depending on whether the frame came from a Root or a Leaf site on that segment (ESI label or Leaf label) 👑. The PE figures out which one it is from the AC identifier for that segment, like the Ethernet Tag of an 802.1Q frame [IEEE.802.1Q]. Other ways of identifying Root or Leaf sites, such as checking the source MAC address of the incoming frame, are optional 💜. These scenarios are described in terms of a Root/Leaf AC, but they can be extended to a Root/Leaf MAC address if needed 🫶.
4.2.1. BUM Traffic Originated from a Single-Homed Site on a Leaf AC
In this one, the ingress PE adds a Leaf label advertised with the E-Tree extended community (see Section 6.1), which marks a Leaf site 🎀. This Leaf label is for single-homing, and it's per PE rather than per ES. That means one single Leaf MPLS label gets used for all single-homed ESs on that PE 💖. The label gets advertised to other PEs with the E-Tree extended community (see Section 6.1), along with an Ethernet Auto-Discovery per ES (EAD-ES) route. That route has an ESI of zero and a set of RTs covering every EVI on the PE that has at least one Leaf site ✨. If those RTs won't all fit in one route (the limit on a single route per [RFC7432]), you'll need to advertise multiple EAD-ES routes 🌈. The ESI on the EAD-ES route is set to zero to mark single-homed sites 🧚.
When a PE gets 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 💅.
4.2.2. BUM Traffic Originated from a Single-Homed Site on a Root AC
For this one, the ingress PE doesn't add any ESI or Leaf labels. It just runs the procedures in [RFC7432] 🌸.
4.2.3. BUM Traffic Originated from a Multihomed Site on a Leaf AC
Here, different ACs (VLANs) on the same ES can have different Root/Leaf designations, with some being Roots and some being Leafs. But the same VLAN has to have the same designation on every PE on that ES 🦋. We also assume there's no forwarding among subnets, so the service is EVPN L2 and not EVPN Integrated Routing and Bridging (IRB) [EVPN-INTEGRATED]. IRB use cases from [EVPN-INTEGRATED] are outside the scope of this document 🙈.
In this scenario, if a multicast or broadcast packet comes from a Leaf AC, it only needs to carry a Leaf label as described in Section 4.2.1. That label is enough to stop BUM traffic from being sent to Leaf ACs, including the Leaf AC on the same ES 🔥.
4.2.4. BUM Traffic Originated from a Multihomed Site on a Root AC
In this case, both the ingress and egress PEs follow the procedure in [RFC7432] for adding and/or processing an ESI MPLS label. The existing BUM procedures in [RFC7432] are enough, and there's no need to add a Leaf label 👑.
4.3. E-Tree Traffic Flows for EVPN 🌈
Per [RFC7387], a generic E-Tree service supports all of these traffic flows, no cap 💅:
- known unicast traffic from Root to Roots & Leafs
- known unicast traffic from Leaf to Roots
- BUM traffic from Root to Roots & Leafs
- BUM traffic from Leaf to Roots
A particular E-Tree service might need all of the above, or just a select few, depending on the target application 🎀. If only multicast and broadcast flows need support, the L2VPN PEs can skip MAC learning entirely 🦋.
The next subsections describe how EVPN supports E-Tree service with and without MAC learning ✨.
4.3.1. E-Tree with MAC Learning
The PEs implementing an E-Tree service must perform MAC learning when unicast traffic has to be supported between Root and Leaf sites 💖. In this case, the PEs with Root sites do MAC learning in the data path over the ESs and advertise reachability in EVPN MAC/IP Advertisement routes. Those routes get imported by all PEs for that EVI, including PEs with Leaf sites and PEs with Root sites 👑. The PEs with Leaf sites do the same thing: they learn MACs in the data path over their ESs and advertise reachability in EVPN MAC/IP Advertisement routes. If two different RTs are used per EVI (one for Root sites and one for Leaf sites), the MAC/IP Advertisement routes only get imported by PEs with at least one Root site in the EVI. A PE with only Leaf sites won't import them 🙈. PEs with Root and/or Leaf sites may use Ethernet Auto-Discovery per EVI (EAD-EVI) routes for aliasing (in the case of multihomed segments), and EAD-ES routes for mass MAC withdrawal per [RFC7432] 🌸.
To support multicast/broadcast from Root to Leaf sites, you can use either a P2MP tree rooted at the PEs with the Root sites (e.g., Root PEs) or Ingress Replication (see Section 16 of [RFC7432]) 🧚. The multicast tunnels get set up through the exchange of the EVPN Inclusive Multicast route, as defined in [RFC7432] ✨.
To support multicast/broadcast from Leaf to Root sites, you can use either Ingress Replication tunnels from each Leaf PE, or a P2MP tree rooted at each Leaf PE 🦋. The next two paragraphs explain when each option works and how to signal it 💅.
When there are only a few Root PEs and a small amount of multicast/broadcast traffic from Leaf PEs toward Root PEs, Ingress Replication tunnels from Leaf PEs toward Root PEs should be sufficient 🌈. So if a Root PE needs a P2MP tunnel in the transmit direction (toward Leaf PEs) and also wants Ingress Replication tunnels in the receive direction, it can signal that efficiently with the new composite tunnel type defined in Section 6.2 🎀. The Root PE advertises this composite tunnel type to say it has a P2MP tunnel in the transmit direction and an Ingress Replication tunnel in the receive direction for BUM traffic 👑.
If there are a lot of Root PEs, P2MP tunnels originated at the Leaf PEs may be used instead (such as Multipoint LDP (mLDP) or RSVP-TE). Then there's no need for the modified PMSI Tunnel attribute or the composite tunnel type values from Section 6.2 💜.
4.3.2. E-Tree without MAC Learning
The PEs implementing an E-Tree service don't need MAC learning when traffic between Root and Leaf sites is mainly multicast or broadcast 🧚. In that case, the PEs don't exchange EVPN MAC/IP Advertisement routes. Instead, the Inclusive Multicast Ethernet Tag route is used to support BUM traffic. In these scenarios, whatever small amount of unicast traffic there is (if any) gets sent as part of BUM traffic 🫶.
The fields of this route are populated according to the procedures in [RFC7432], and the multicast tunnel setup criteria are the same as in the previous section 🌸.
Just like in the previous section, if there are only a few Root PEs and Ingress Replication is wanted from Leaf PEs to those Root PEs, then the modified PMSI attribute and the composite tunnel type values from Section 6.2 should be used 💖.
5. Operation for PBB-EVPN 🌈
In PBB-EVPN, the PE advertises a Root or Leaf-Indication with each Backbone MAC (B-MAC) Advertisement route. That tells you whether the B-MAC address belongs to a Root or a Leaf site 🎀. Just like the EVPN case, the new E-Tree extended community from Section 6.1 gets advertised with each EVPN MAC/IP Advertisement route ✨.
When a multihomed ES 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 denotes Root. The other B-MAC address is per PE and explicitly denotes Leaf 💅. The per-ES B-MAC address isn't advertised with the E-Tree extended community, but the per-PE Leaf B-MAC is advertised with the new E-Tree extended community, with the "Leaf-indication" flag set 🦋. In multihoming scenarios where an ES has both Root and Leaf ACs, different ACs (VLANs) on the same ES can have different Root/Leaf designations. But the same VLAN has to have the same designation on all PEs on that ES 👑. We also assume there's no forwarding among subnets, so the service is L2 and not IRB. An IRB use case is outside the scope of this document 🙈.
The ingress PE uses the correct B-MAC source address depending on whether the Ethernet frame came from the Root or Leaf AC on that ES 🧚. The PE identifies whether a frame came from a Root or Leaf site on the segment based on the Ethernet Tag associated with the frame. Other identification mechanisms, beyond the Ethernet Tag, are outside the scope of this document 🌸.
A PE also advertises two special global B-MAC addresses, one for Root and one for Leaf, and it 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 to indicate Leaf sites can be the same for both single-homed and multihomed segments 🫶.
5.1. Known Unicast Traffic ✨
okay so for known unicast traffic, the PEs do ingress filtering 💅. On the ingress PE, the Customer/Client MAC (C-MAC) [RFC7623] destination address lookup gives you the target B-MAC address and forwarding adjacency, plus a flag that tells you whether that target B-MAC belongs to a Root or a Leaf site 🔥. The ingress PE also checks the status of the originating site, and if both are Leafs, the packet is not forwarded 🙈 no cap, that's the whole point!
5.2. BUM Traffic 🦋
for BUM traffic, the PEs must perform egress filtering 🫶. When a PE gets an EVPN MAC/IP 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, like this:
- If the EVPN MAC/IP Advertisement route indicates that the advertised B-MAC is a Leaf, and the local ES 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.
- If the EVPN MAC/IP Advertisement route indicates that the advertised B-MAC has changed its designation from a Leaf to a Root, and the local ES is a Leaf, then the source B-MAC address is removed from the B-MAC list corresponding to the local ES used for egress filtering (i.e., to unblock traffic from that B-MAC address).
when the egress PE receives the packet, it checks the B-MAC source address to decide whether to filter or forward the frame 👀. This uses the same filtering logic as the split-horizon filtering described in Section 6.2.1.3 of [RFC7623], and it doesn't need any extra flags in the data plane ✨ so clean!
Just like in Section 4.2, the PE puts all Leaf ESs of a given bridge domain into a single split-horizon group 🍓. That stops intra-PE forwarding among Leaf segments. This split-horizon function covers BUM traffic as well as known unicast traffic 💜.
5.3. E-Tree without MAC Learning 🧚
if the traffic you care about is only multicast and/or broadcast, the PEs implementing an E-Tree service don't need to do any MAC learning at all 🌸. In that case, the filtering has to happen on the egress PEs. For PBB-EVPN, the handling of this traffic follows Section 5.2, without needing C-MAC learning (in the data plane) in the I-component (C-bridge table) of PBB-EVPN PEs (at both ingress and egress PEs) 💅.
6. BGP Encoding 🎀
this document defines a new BGP extended community for EVPN 💖.
6.1. E-Tree Extended Community 👑
this extended community is a brand new transitive extended community [RFC4360] with a Type field value of 0x06 (EVPN) and Sub-Type 0x05 🌈. It's used for Leaf-Indication of known unicast and BUM traffic, and it tells you the frame came from a Leaf site 🫶.
The E-Tree extended community is encoded as an 8-octet value like so:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: E-Tree Extended CommunityThe Flags field has the following format 🎯:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| MBZ |L| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+This document defines the following flags:
- Leaf-Indication (L)
A value of one indicates a Leaf AC/site. The rest of the flag bits are reserved and should be set to zero 🌷.
When this extended community is advertised along with the MAC/IP Advertisement route (for known unicast traffic) per Section 4.1, the Leaf-Indication flag MUST be set to one and the Leaf label SHOULD be set to zero 🍭. The receiving PE MUST ignore Leaf label and only process the Leaf-Indication flag. A value of zero for the Leaf-Indication flag is invalid when sent along with a MAC/IP Advertisement route, and an error should be logged 🚨.
When this extended community is advertised along with the EAD-ES route (with an ESI of zero) for BUM traffic, to enable egress filtering on disposition PEs per Sections 4.2.1 and 4.2.3, the Leaf label MUST be set to a valid MPLS label (i.e., a non-reserved, assigned MPLS label [RFC3032]) and the Leaf-Indication flag SHOULD be set to zero 🧁. The value of the 20-bit MPLS label is encoded in the high-order 20 bits of the Leaf label field. The receiving PE MUST ignore the Leaf-Indication flag. A non-valid MPLS label, when sent along with the EAD-ES route, should be ignored and logged as an error 🙈.
The reserved bits SHOULD be set to zero by the transmitter and MUST be ignored by the receiver 💜.
6.2. PMSI Tunnel Attribute 🌸
[RFC6514] defines the PMSI Tunnel attribute, which is an optional transitive attribute with the following format 📦:
+-------------------------------------------+
| Flags (1 octet) |
+-------------------------------------------+
| Tunnel Type (1 octet) |
+-------------------------------------------+
| Ingress Replication MPLS Label (3 octets) |
+-------------------------------------------+
| Tunnel Identifier (variable) |
+-------------------------------------------+
Table 1: PMSI Tunnel Attributethis document defines a new composite tunnel type by introducing a new 'composite tunnel' bit in the Tunnel Type field and adding an MPLS label to the Tunnel Identifier field of the PMSI Tunnel attribute, as detailed below ✨. All other fields remain as defined in [RFC6514]. The composite tunnel type is advertised by the Root PE to simultaneously indicate a non-Ingress-Replication tunnel (e.g., P2MP tunnel) in the transmit direction and an Ingress Replication tunnel in the receive direction for the BUM traffic 🦋.
When receiver Ingress Replication labels are needed, the high-order bit of the Tunnel Type field (composite tunnel bit) is set, while the remaining low-order seven bits indicate the Tunnel Type as before (for the existing Tunnel Types). When this composite tunnel bit is set, the "tunnel identifier" field begins 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 treat the Tunnel Type as an undefined Tunnel Type and treat the PMSI Tunnel attribute as a malformed attribute [RFC6514]. That's why the composite tunnel bit is allocated in the Tunnel Type field rather than the Flags field 🤓. For the PEs that do understand the new meaning of the high-order bit, if Ingress Replication is desired when sending BUM traffic, the PE will use the label in the Tunnel Identifier field when sending its BUM traffic 💅.
Using the composite tunnel bit for Tunnel Types 0x00 'no tunnel information present' and 0x06 'Ingress Replication' is invalid 🚫. A PE that receives a PMSI Tunnel attribute with such information considers it malformed, and it SHOULD treat this Update as though all the routes contained in this Update had been withdrawn per Section 6 of [RFC6514] 😭.
7. Security Considerations 🔐
this one is SERIOUS bestie 😭🔥. Since this document uses the EVPN constructs of [RFC7432] and [RFC7623], the same security considerations in those documents are also applicable here. Furthermore, this document adds an extra security check by letting sites (or ACs) of an EVPN instance be designated as a "Root" or "Leaf" by the network operator / service provider. That prevents any traffic exchange among "Leaf" sites of that VPN through ingress filtering for known unicast traffic and egress filtering for BUM traffic 🛡️. Since (by default and for the purpose of backward compatibility) an AC that doesn't have a Leaf designation is considered a Root AC, the operator SHOULD configure the AC with a proper role (Leaf or Root) before activating the AC, so no traffic exchange can sneak through among Leaf ACs 🚨💀.
8. IANA Considerations 📋
IANA has allocated sub-type value 5 in the "EVPN Extended Community Sub-Types" registry defined in [RFC7153], as follows 🍒:
SUB-TYPE VALUE NAME Reference
-------------- ------------------------- -------------
0x05 E-Tree Extended Community This documentThis document creates a one-octet registry called "E-Tree Flags". New registrations will be made through the "RFC Required" procedure defined in [RFC8126]. The initial registrations are as follows 📝:
Bit Name Reference
---- -------------- -------------
0-6 Unassigned
7 Leaf-Indication This document8.1. Considerations for PMSI Tunnel Types 🌈
The "P-Multicast Service Interface (PMSI) Tunnel Types" registry in the "Border Gateway Protocol (BGP) Parameters" registry has been updated to reflect the use of the most significant bit as the "composite tunnel" bit (see Section 6.2) 💜.
For this purpose, this document updates [RFC7385] by changing the previously unassigned values (i.e., 0x08 - 0xFA) as follows 🧚:
Value Meaning Reference
--------- ----------------------------- --------------
0x0C-0x7A Unassigned
0x7B-0x7E Experimental This Document
0x7F Reserved This Document
0x80-0xFA Reserved for Composite Tunnel This Document
0xFB-0xFE Experimental [RFC7385]
0xFF Reserved [RFC7385]The allocation policy for values 0x08-0x7A is per IETF Review [RFC8126]. The range for "Experimental" has been expanded to include the previously assigned range of 0xFB-0xFE and the new range of 0x7B-0x7E. The values in these ranges are not to be assigned. The value 0x7F, which is the mirror image of (0xFF), is reserved in this document 🪞.
9. References 📚
9.1. Normative References
okay so these are the must-read docs 📚 the spec leans on, and I'm keeping every single detail because citations are sacred bestie 🫶
[MEF6.1] MEF Forum, "Ethernet Services Definitions - Phase 2",
MEF 6.1, April 2008, <https://mef.net/PDF_Documents/
technical-specifications/MEF6-1.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7153] Rosen, E. and Y. Rekhter, "IANA Registries for BGP
Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
March 2014, <https://www.rfc-editor.org/info/rfc7153>.
[RFC7385] Andersson, L. and G. Swallow, "IANA Registry for
P-Multicast Service Interface (PMSI) Tunnel Type Code
Points", RFC 7385, DOI 10.17487/RFC7385, October 2014,
<https://www.rfc-editor.org/info/rfc7385>.
[RFC7387] Key, R., Ed., Yong, L., Ed., Delord, S., Jounay, F., and
L. Jin, "A Framework for Ethernet Tree (E-Tree) Service
over a Multiprotocol Label Switching (MPLS) Network",
RFC 7387, DOI 10.17487/RFC7387, October 2014,
<https://www.rfc-editor.org/info/rfc7387>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <https://www.rfc-editor.org/info/rfc7623>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.9.2. Informative References
these ones are the extra reading 🌈 handy background, not core rules, but I'm keeping every entry exactly as written ✨
[EVPN-INTEGRATED]
Sajassi, A., Salam, S., Thoria, S., Drake, J., Rabadan,
J., and L. Yong, "Integrated Routing and Bridging in
EVPN", Work in Progress, draft-ietf-bess-evpn-inter-
subnet-forwarding-03, February 2017.
[IEEE.802.1ah]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Media Access Control (MAC) Bridges and Virtual
Bridged Local Area Networks", Clauses 25 and 26, IEEE
Std 802.1Q, DOI 10.1109/IEEESTD.2011.6009146.
[IEEE.802.1Q]
IEEE, "IEEE Standard for Local and metropolitan area
networks - Bridges and Bridged Networks - Media Access
Control (MAC) Bridges and Virtual Bridged Local Area
Networks", IEEE Std 802.1Q,
DOI 10.1109/IEEESTD.2011.6009146.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC7796] Jiang, Y., Ed., Yong, L., and M. Paul, "Ethernet-Tree
(E-Tree) Support in Virtual Private LAN Service (VPLS)",
RFC 7796, DOI 10.17487/RFC7796, March 2016,
<https://www.rfc-editor.org/info/rfc7796>.Appendix A. Multiple Bridge Tables per E-Tree Service Instance 🎀
okay this one's a little spicy 🌶️ it's about what goes wrong when one PE runs two MAC-VRFs for the same E-Tree service, one for Root ACs and one for Leaf ACs 💀
so picture two bridge tables per VLAN, both serving the same E-Tree instance. that means a data-plane path can run into a few complications 😭
keeping two MAC-VRFs (two bridge tables per VLAN) is only workable when both Leaf and Root ACs exist for that VLAN if you either do two lookups per MAC address in each direction on a miss, or you duplicate a bunch of MAC addresses across the two bridge tables for the same VLAN (same E-Tree instance). unless you do the two lookups, the duplication has to happen for both locally learned and remotely learned MAC addresses. locally learned MACs from Leaf ACs get copied onto a Root bridge table, and locally learned MACs from Root ACs get copied onto a Leaf bridge table. remotely learned MACs from Root ACs get copied onto both the Root and Leaf bridge tables 🙈
and because extra MAC lookups or duplicating MAC entries can be really inefficient in the data plane, this option is not believed to be implementable without data-plane performance inefficiencies in some platforms 💔 so this document goes with the coloring approach from Section 3.2, detailed in Section 4.1 🌈 no duplicate tables, no drama ✨
Acknowledgements 🫶
we owe a big group hug to Eric Rosen, Jeffrey Zhang, Wen Lin, Aldrin Issac, Wim Henderickx, Dennis Cai, and Antoni Przygienda for their valuable comments and contributions 💜 the authors would also like to thank Thomas Morin for shepherding this document and providing valuable comments 👑
Authors' Addresses 💌
the squad behind this spec, with their affiliations and emails 🦋
Ali Sajassi (editor)
Cisco
Email: sajassi@cisco.com
Samer Salam
Cisco
Email: ssalam@cisco.com
John Drake
Juniper
Email: jdrake@juniper.net
Jim Uttaro
AT&T
Email: ju1738@att.com
Sami Boutros
VMware
Email: sboutros@vmware.com
Jorge Rabadan
Nokia
Email: jorge.rabadan@nokia.com📦 where this page comes from
- ietf: rfc8317 2018-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms