Multicast Source Redundancy in EVPN Networks
draft-ietf-bess-evpn-redundant-mcast-source-06
| Document | Type | Active Internet-Draft (bess WG) | |
|---|---|---|---|
| Authors | Jorge Rabadan , Jayant Kotalwar , Senthil Sathappan , Zhaohui (Jeffrey) Zhang , Wen Lin , Eric C. Rosen | ||
| Last updated | 2023-06-27 | ||
| Replaces | draft-skr-bess-evpn-redundant-mcast-source | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | Mankamana Prasad Mishra | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | mankamis@cisco.com |
draft-ietf-bess-evpn-redundant-mcast-source-06
BESS Workgroup J. Rabadan, Ed.
Internet-Draft J. Kotalwar
Intended status: Standards Track S. Sathappan
Expires: 29 December 2023 Nokia
Z. Zhang
W. Lin
Juniper
E. Rosen
Individual
27 June 2023
Multicast Source Redundancy in EVPN Networks
draft-ietf-bess-evpn-redundant-mcast-source-06
Abstract
Ethernet Virtual Private Network (EVPN) supports intra and inter-
subnet IP multicast forwarding. However, EVPN (or conventional IP
multicast techniques for that matter) do not have a solution for the
case where the following two statements are true at the same time: a)
a given multicast group carries more than one flow (i.e., more than
one source), and b) it is desired that each receiver gets only one of
the several flows. Existing multicast techniques assume there are no
redundant sources sending the same flow to the same IP multicast
group, and, in case there were redundant sources, the receiver's
application would deal with the received duplicated packets. This
document extends the existing EVPN specifications and assumes that IP
Multicast source redundancy may exist. It also assumes that, in case
two or more sources send the same IP Multicast flows into the tenant
domain, the EVPN PEs need to avoid that the receivers get packet
duplication by following the described procedures.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
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This Internet-Draft will expire on 29 December 2023.
Copyright Notice
Copyright (c) 2023 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, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Background on IP Multicast Delivery in EVPN Networks . . 7
1.2.1. Intra-subnet IP Multicast Forwarding . . . . . . . . 7
1.2.2. Inter-subnet IP Multicast Forwarding . . . . . . . . 8
1.3. Multi-Homed IP Multicast Sources in EVPN . . . . . . . . 10
1.4. The Need for Redundant IP Multicast Sources in EVPN . . . 12
2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 12
3. BGP EVPN Extensions . . . . . . . . . . . . . . . . . . . . . 14
4. Warm Standby (WS) Solution for Redundant G-Sources . . . . . 15
4.1. Warm Standby Example in an OISM Network . . . . . . . . . 17
4.2. Warm Standby Example in a Single-BD Tenant Network . . . 19
5. Hot Standby (HS) Solution for Redundant G-Sources . . . . . . 20
5.1. Extensions for the Advertisement of DCB Labels . . . . . 24
5.2. Use of BFD in the HS Solution . . . . . . . . . . . . . . 25
5.3. Hot Standby Example in an OISM Network . . . . . . . . . 25
5.4. Hot Standby Example in a Single-BD Tenant Network . . . . 29
6. Security Considerations . . . . . . . . . . . . . . . . . . . 29
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Normative References . . . . . . . . . . . . . . . . . . 30
8.2. Informative References . . . . . . . . . . . . . . . . . 31
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 32
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
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1. Introduction
Intra and Inter-subnet IP Multicast forwarding are supported in EVPN
networks. [RFC9251] describes the procedures required to optimize
the delivery of IP Multicast flows when Sources and Receivers are
connected to the same EVPN Broadcast Domain, whereas
[I-D.ietf-bess-evpn-irb-mcast] specifies the procedures to support
Inter-subnet IP Multicast in a tenant network. Inter-subnet IP
Multicast means that IP Multicast Source and Receivers of the same
multicast flow are connected to different Broadcast Domains of the
same tenant.
[RFC9251], [I-D.ietf-bess-evpn-irb-mcast] or conventional IP
multicast techniques do not have a solution for the case where the
following two statements are true at the same time: a) a given
multicast group carries more than one flow (i.e., more than one
source) and b) it is desired that each receiver gets only one of the
several flows. Multicast techniques assume there are no redundant
sources sending the same flows to the same IP multicast group, and,
in case there were redundant sources, the receiver's application
would deal with the received duplicated packets.
As a workaround in conventional IP multicast (that is, networks
running PIM or MVPN), if all the redundant sources are given the same
IP address, each receiver will get only one flow. The reason is
that, in conventional IP multicast, the RP (Rendezvous Point) always
creates (S,G) state, and the Last Hop Router (LHR) sometimes creates
(S,G) state. The (S,G) state always binds the (S,G) flow to a
source-specific tree, rooted at the source IP address. If multiple
sources have the same IP address, one may end up with multiple (S,G)
trees. However, the way the trees are constructed ensures that any
given Last Hop Router or Rendezvous Point router is on at most one of
them. The use of an anycast address assigned to multiple sources may
be useful for warm standby redundancy solutions (Section 2).
However, on one hand, it is not really helpful for hot standby
redundancy solutions (Section 2) and on the other hand, configuring
the same IP address (in particular, the same IPv4 address) in
multiple sources may bring issues if the sources need to be reached
by IP unicast traffic or if the sources are attached to the same
Broadcast Domain.
In addition, in the scenario where several multicast sources
streaming traffic to the same group are attached via EVPN/OISM
(Optimized Inter-Subnet Multicast), there is not necessarily any
(S,G) state created for the redundant sources. The Last Hop Routers
may have only (*,G) state, and there may not be a Rendezvous Point
router (creating (S,G) state) either. Therefore, this document
extends the above two specifications and assumes that IP Multicast
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source redundancy may exist. It also assumes that, in case two or
more sources send the same IP Multicast flows into the tenant domain,
the EVPN PEs need to avoid that the receivers get packet duplication.
The procedures to handle redundant sources in solutions different
than [RFC9251] or [I-D.ietf-bess-evpn-irb-mcast] are out of the scope
of this document.
The solution provides support for Warm Standby (WS) and Hot Standby
(HS) redundancy. WS is defined as the redundancy scenario in which
the upstream PEs, attached to the redundant sources of the same
tenant, make sure that only one source of the same flow can send
multicast to the interested downstream PEs at the same time. In HS
mode, the upstream PEs forward the redundant multicast flows to the
downstream PEs, and the downstream PEs make sure only one flow is
forwarded to the interested attached receivers.
1.1. Terminology
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.
* Broadcast Domain (BD): an emulated ethernet, such that two systems
on the same BD will receive each other's link-local broadcasts.
In this document, BD also refers to the instantiation of a
Broadcast Domain on an EVPN PE. An EVPN PE can be attached to one
or multiple BDs of the same tenant.
* BUM: Broadcast, Unknown unicast and Multicast traffic.
* Designated Forwarder (DF): as defined in [RFC7432], an ethernet
segment may be multi-homed (attached to more than one PE). An
ethernet segment may also contain multiple BDs, of one or more
EVIs. For each such EVI, one of the PEs attached to the segment
becomes that EVI's DF for that segment. Since a BD may belong to
only one EVI, we can speak unambiguously of the BD's DF for a
given segment.
* Downstream PE: in this document a Downstream PE is referred to as
the EVPN PE that is connected to the IP Multicast receivers and
gets the IP Multicast flows from remote EVPN PEs.
* G-traffic: any frame with an IP payload whose IP Destination
Address (IP DA) is a multicast group G.
* G-source: any system sourcing IP multicast traffic to group G.
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* IGMP: Internet Group Management Protocol.
* Inclusive Multicast Tree or Inclusive Provider Multicast Service
Interface (I-PMSI): defined in [RFC6513], in this document it is
applicable only to EVPN and refers to the default multicast tree
for a given BD. All the EVPN PEs that are attached to a specific
BD belong to the I-PMSI for the BD. The I-PMSI trees are signaled
by EVPN Inclusive Multicast Ethernet Tag (IMET) routes.
* IMET route: EVPN Inclusive Multicast Ethernet Tag route, as in
[RFC7432].
* MLD: Multicast Listener Discovery.
* MVPN: Multicast Virtual Private Networks, as in [RFC6513].
* OISM: Optimized Inter-Subnet Multicast, as in
[I-D.ietf-bess-evpn-irb-mcast].
* PIM: Protocol Independent Multicast, as in [RFC7761].
* P-tunnel: Provider tunnel refers to the type of tree a given
upstream EVPN PE uses to forward multicast traffic to downstream
PEs. Examples of P-tunnels supported in this document are Ingress
Replication (IR), Assisted Replication (AR), Bit Indexed Explicit
Replication (BIER), multicast Label Distribution Protocol (mLDP)
or Point to Multi-Point Resource Reservation protocol with Traffic
Engineering extensions (P2MP RSVP-TE).
* Redundant G-source: a host or router that transmits an SFG in a
tenant network where there are more hosts or routers transmitting
the same SFG. Redundant G-sources for the same SFG SHOULD have
different IP addresses, although they MAY have the same IP address
when in different BDs of the same tenant network. Redundant
G-sources are assumed NOT to be "bursty" in this document (typical
example are Broadcast TV G-sources or similar).
* S-ES and S-ESI: multicast Source Ethernet Segment and multicast
Source Ethernet Segment Identifier. The Ethernet Segment and
Ethernet Segment Identifier associated to a G-source.
* Selective Multicast Tree or Selective Provider Multicast Service
Interface (S-PMSI): defined in [RFC6513], in this document it is
applicable only to EVPN and refers to the multicast tree to which
only the interested PEs of a given BD belong to. There are two
types of EVPN S-PMSIs:
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- EVPN S-PMSIs that require the advertisement of S-PMSI Auto-
Discovery (S-PMSI A-D) routes from the upstream PE, as in
[I-D.ietf-bess-evpn-bum-procedure-updates]. The interested
downstream PEs join the S-PMSI tree as in
[I-D.ietf-bess-evpn-bum-procedure-updates].
- EVPN S-PMSIs that don't require the advertisement of S-PMSI AD
routes. They use the forwarding information of the IMET
routes, but upstream PEs send IP Multicast flows only to
downstream PEs issuing Selective Multicast Ethernet Tag (SMET)
routes for the flow. These S-PMSIs are only supported with the
following P-tunnels: Ingress Replication (IR), Assisted
Replication (AR) and BIER.
* SFG: Single Flow Group, i.e., a multicast group which represents
traffic that contains only a single flow. Multiple sources - with
the same or different IP - may be transmitting an SFG. An SFG is
represented as (*,G) if any source that issues multicast traffic
to G is a redundant G-source. An SFG can also be represented as
(S,G), where S is a prefix of any length. In this case, a source
is considered a redundant G-source for the SFG if it is contained
in the prefix.
* SMET route: Selective Multicast Ethernet Tag route, as in
[RFC9251].
* (S,G) and (*,G): used to describe multicast packets or multicast
state. S stands for Source (IP address of the multicast traffic)
and G stands for the Group or multicast destination IP address of
the group. An (S,G) multicast packet refers to an IP packet with
source IP address "S" and destination IP address "G", and it is
forwarded on a multicast router if there is a corresponding state
for (S,G). A (*,G) multicast packet refers to an IP packet with
"any" source IP address and a destination IP address "G", and it
is forwarded on a multicast router based on the existance of the
corresponding (*,G) state. The document uses variations of these
terms. For example, (S1,G1) represents the multicast packets or
multicast state for source IP address "S1" and group IP address
"G1".
* Upstream PE: in this document an Upstream PE is referred to as the
EVPN PE that is connected to the IP Multicast source or closest to
it. It receives the IP Multicast flows on local ACs (Attachment
Circuits).
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This document also assumes familiarity with the terminology of
[RFC7432], [RFC4364], [RFC6513], [RFC6514], [RFC9251],
[I-D.ietf-bess-evpn-irb-mcast], [RFC9136] and
[I-D.ietf-bess-evpn-bum-procedure-updates].
1.2. Background on IP Multicast Delivery in EVPN Networks
IP Multicast is all about forwarding a single copy of a packet from a
source S to a group of receivers G along a multicast tree. That
multicast tree can be created in an EVPN tenant domain where S and
the receivers for G are connected to the same Broadcast Domain or
different Broadcast Domain. In the former case, we refer to Intra-
subnet IP Multicast forwarding, whereas the latter case will be
referred to as Inter-subnet IP Multicast forwarding.
1.2.1. Intra-subnet IP Multicast Forwarding
When the source S1 and receivers interested in G1 are attached to the
same Broadcast Domain, the EVPN network can deliver the IP Multicast
traffic to the receivers in two different ways (Figure 1):
S1 + S1 +
(a) + | (b) + |
| | (S1,G1) | | (S1,G1)
PE1 | | PE1 | |
+-----+ v +-----+ v
|+---+| |+---+|
||BD1|| ||BD1||
|+---+| |+---+|
+-----+ +-----+
+-------|-------+ +-------|
| | | | |
v v v v v
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|+---+| |-----| |-----| |+---+| |+---+| |+---+|
||BD1|| ||BD1|| ||BD1|| ||BD1|| ||BD1|| ||BD1||
|+---+| |-----| |-----| |+---+| |+---+| |+---+|
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
PE2| PE3| PE4| PE2| PE3| PE4
- | - - - | - | - | - - - | -
| | | | | | | | |
v v v v v
| R1 R2 | R3 | R1 R2 | R3
- - - G1- - - - - - G1- - -
Figure 1: Intra-subnet IP Multicast
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Model (a) illustrated in Figure 1 is referred to as "IP Multicast
delivery as BUM traffic". This way of delivering IP Multicast
traffic does not require any extensions to [RFC7432], however, it
sends the IP Multicast flows to non-interested receivers, such as
e.g., R3 in Figure 1. In this example, downstream PEs can snoop
IGMP/MLD messages from the receivers so that layer-2 multicast state
is created and, for instance, PE4 can avoid sending (S1,G1) to R3,
since R3 is not interested in (S1,G1).
Model (b) in Figure 1 uses an S-PMSI to optimize the delivery of the
(S1,G1) flow. For instance, assuming PE1 uses IR, PE1 sends (S1,G1)
only to the downstream PEs that issued an SMET route for (S1,G1),
that is, PE2 and PE3. In case PE1 uses any P-tunnel different than
IR, AR or BIER, PE1 will advertise an S-PMSI A-D route for (S1,G1)
and PE2/PE2 will join that tree.
Procedures for Model (b) are specified in [RFC9251].
1.2.2. Inter-subnet IP Multicast Forwarding
If the source and receivers are attached to different BDs of the same
tenant domain, the EVPN network can also use Inclusive or Selective
Trees as depicted in Figure 2, models (a) and (b) respectively.
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S1 + S1 +
(a) + | (b) + |
| | (S1,G1) | | (S1,G1)
PE1 | | PE1 | |
+-----+ v +-----+ v
|+---+| |+---+|
||BD1|| ||BD1||
|+---+| |+---+|
+-----+ +-----+
+-------|-------+ +-------|
| | | | |
v v v v v
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+
|+---+| |+---+| |+---+| |+---+| |+---+| |+---+|
||SBD|| ||SBD|| ||SBD|| ||SBD|| ||SBD|| ||SBD||
|+-|-+| |+-|-+| |+---+| |+-|-+| |+-|-+| |+---+|
| VRF | | VRF | | VRF | | VRF | | VRF | | VRF |
|+-v-+| |+-v-+| |+---+| |+-v-+| |+-v-+| |+---+|
||BD2|| ||BD3|| ||BD4|| ||BD2|| ||BD3|| ||BD4||
|+-|-+| |+-|-+| |+---+| |+-|-+| |+-|-+| |+---+|
+--|--+ +--|--+ +-----+ +--|--+ +--|--+ +-----+
PE2| PE3| PE4 PE2| PE3| PE4
- | - - - | - - | - - - | -
| | | | | | | |
v v v v
| R1 R2 | R3 | R1 R2 | R3
- - - G1- - - - - - G1- - -
Figure 2: Inter-subnet IP Multicast
[I-D.ietf-bess-evpn-irb-mcast] specifies the procedures to optimize
the Inter-subnet Multicast forwarding in an EVPN network. The IP
Multicast flows are always sent in the context of the source BD. As
described in [I-D.ietf-bess-evpn-irb-mcast], if the downstream PE is
not attached to the source BD, the IP Multicast flow is received on
the SBD (Supplementary Broadcast Domain), as in the example in
Figure 2.
[I-D.ietf-bess-evpn-irb-mcast] supports Inclusive or Selective
Multicast Trees, and as explained in Section 1.2.1, the Selective
Multicast Trees are setup in a different way, depending on the
P-tunnel being used by the source Broadcast Domain. As an example,
model (a) in Figure 2 illustrates the use of an Inclusive Multicast
Tree for Broadcast Domain BD1 on PE1. Since the downstream PEs are
not attached to BD1, they will all receive (S1,G1) in the context of
the Supplementary Broadcast Domain (SBD) and will locally route the
flow to the local Attachment Circuits. Model (b) uses a similar
forwarding model, however PE1 sends the (S1,G1) flow in a Selective
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Multicast Tree. If the P-tunnel is Ingress Replication (IR),
Assisted Replication (AR) or Bit Index Explicit Replication (BIER),
PE1 does not need to advertise an S-PMSI A-D route.
[I-D.ietf-bess-evpn-irb-mcast] is a superset of the procedures in
[RFC9251], in which sources and receivers can be in the same or
different Broadcast Domain of the same tenant.
[I-D.ietf-bess-evpn-irb-mcast] ensures every upstream PE attached to
a source will learn of all other PEs (attached to the same Tenant
Domain) that have interest in a particular set of flows. This is
because the downstream PEs advertise SMET routes for a set of flows
with the Supplementary Broadcast Domain's Route Target and they are
imported by all the Upstream PEs of the tenant. As a result of that,
inter-subnet multicasting can be done within the Tenant Domain,
without requiring any Rendezvous Points (RP), shared trees, Upstream
Multicast Hop (UMH) selection or any other complex aspects of
conventional multicast routing techniques.
1.3. Multi-Homed IP Multicast Sources in EVPN
Contrary to conventional multicast routing technologies, multi-homing
PEs attached to the same source can never create IP Multicast packet
duplication if the PEs use a multi-homed Ethernet Segment (ES).
Figure 3 illustrates this by showing two multi-homing PEs (PE1 and
PE2) that are attached to the same source (S1). We assume that S1 is
connected to an all-active Ethernet Ssegment by a layer-2 switch
(SW1) with a Link Aggregation Group (LAG) to PE1 and PE2.
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S1
|
v
+-----+
| SW1 |
+-----+
+---- | |
(S1,G1)| +----+ +----+
IGMP | | all-active |
J(S1,G1) PE1 v | ES-1 | PE2
+----> +-----------|---+ +---|-----------+
| +---+ +---+ | | +---+ |
R1 <-----|BD2| |BD1| | | |BD1| |
| +---+---+---+ | | +---+---+ |
+----| |VRF| | | | |VRF| |----+
| | +---+---+ | | | +---+---+ | |
| | |SBD| | | | |SBD| | |
| | +---+ | | | +---+ | |
| +------------|--+ +---------------+ |
| | |
| | |
| | |
| EVPN | ^ |
| OISM v PE3 | SMET |
| +---------------+ | (*,G1) |
| | +---+ | | |
| | |SBD| | |
| | +---+---+ | |
+--------------| |VRF| |----------------+
| +---+---+---+ |
| |BD2| |BD3| |
| +-|-+ +-|-+ |
+---|-------|---+
^ | | ^
IGMP | v v | IGMP
J(*,G1) | R2 R3 | J(S1,G1)
Figure 3: All-active Multi-homing and OISM
When receiving the (S1,G1) flow from S1, SW1 will choose only one
link to send the flow, as per [RFC7432]. Assuming PE1 is the
receiving PE on Broadcast Domain BD1, the IP Multicast flow will be
forwarded as soon as BD1 creates multicast state for (S1,G1) or
(*,G1). In the example of Figure 3, receivers R1, R2 and R3 are
interested in the multicast flow to G1. R1 will receive (S1,G1)
directly via the IRB interface as per [I-D.ietf-bess-evpn-irb-mcast].
Upon receiving IGMP reports from R2 and R3, PE3 will issue an SMET
(*,G1) route that will create state in PE1's Broadcast Domain BD1.
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PE1 will therefore forward the IP Multicast flow to PE3's SBD and PE3
will forward to R2 and R3, as per [I-D.ietf-bess-evpn-irb-mcast]
procedures.
When IP Multicast source multi-homing is required, EVPN multi-homed
Ethernet Segments MUST be used. EVPN multi-homing guarantees that
only one Upstream PE will forward a given multicast flow at the time,
avoiding packet duplication at the Downstream PEs. In addition, the
SMET route for a given flow creates state in all the multi-homing
Upstream PEs. Therefore, in case of failure on the Upstream PE
forwarding the flow, the backup Upstream PE can forward the flow
immediately.
This document assumes that multi-homing PEs attached to the same
source always use multi-homed Ethernet Segments.
1.4. The Need for Redundant IP Multicast Sources in EVPN
While multi-homing PEs to the same IP Multicast G-source provides
certain level of resiliency, multicast applications are often
critical in the Operator's network and greater level of redundancy is
required. This document assumes that:
a. Redundant G-sources for an Single Flow Group (SFG) may exist in
the EVPN tenant network. A Redundant G-source is a host or a
router that sends an Single Flow Group stream in a tenant network
where there is another host or router sending traffic to the same
Single Flow Group.
b. Those redundant G-sources may be in the same Broadcast Domain or
different Broadcast Domains of the tenant. There must not be
restrictions imposed on the location of the receiver systems
either.
c. The redundant G-sources can be single-homed to only one EVPN PE
or multi-homed to multiple EVPN PEs.
d. The EVPN PEs must avoid duplication of packets of the same Single
Flow Group on the receiver systems.
2. Solution Overview
An Single Flow Group (SFG) is represented as (*,G) if any source that
issues multicast traffic to G is a redundant G-source.
Alternatively, this document allows a Single Flow Group to be
represented as (S,G), where the source IP address "S" is a prefix of
any length. In this case, a source is considered a redundant
G-source for the Single Flow Group if it is contained in the prefix.
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This document allows variable length prefixes in the Sources
advertised in S-PMSI A-D routes only for the particular application
of redundant G-sources.
There are two redundant G-source solutions described in this
document:
* Warm Standby (WS) Solution
* Hot Standby (HS) Solution
The Warm Standby solution is considered an upstream-PE-based solution
(since downstream PEs do not participate in the procedures), in which
all the upstream PEs attached to redundant G-sources for a Single
Flow Group represented by (*,G) or (S,G) will elect a "Single
Forwarder" (SF) among themselves. Once a Single Forwarder is
elected, the upstream PEs add an Reverse Path Forwarding (RPF) check
to the (*,G) or (S,G) state for the Single Flow Group:
* A non-Single Forwarder upstream PE discards any (*,G)/(S,G)
packets received over a local Attachment Circuit.
* The Single Forwarder accepts and forwards any (*,G)/(S,G) packets
it receives over a single local Attachment Circuit (for the Single
Flow Group). In case (*,G)/(S,G) packets for the Single Flow
Group are received over multiple local Attachment Circuits, they
will be discarded in all the local Attachment Circuits but one.
The procedure to choose the local Attachment Circuit that accepts
packets is a local implementation matter.
A failure on the Single Forwarder will result in the election of a
new Single Forwarder. The Election requires BGP extensions on the
existing EVPN routes. These extensions and associated procedures are
described in Section 3 and Section 4 respectively.
In the Hot Standby solution the downstream PEs are the ones avoiding
the Single Flow Group duplication. The upstream PEs are aware of the
locally attached G-sources and add a unique Ethernet Segment
Identifier label (ESI-label) per Single Flow Group to the multicast
packets forwarded to downstream PEs. The downstream PEs pull the
Single Flow Group from all the upstream PEs attached to the redundant
G-sources and avoid duplication on the receiver systems by adding a
Reverse Path Forwarding check to the (*,G) state for the Single Flow
Group:
* A downstream PE discards any (*,G) packets it receives from the
"wrong G-source".
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* The wrong G-source is identified in the data path by an Ethernet
Segment Identifier label that is different than the Ethernet
Segment Identifier label used for the selected G-source.
* Note that the Ethernet Segment Identifier label is used here for
"ingress filtering" (at the egress/downstream PE) as opposed to
the [RFC7432] "egress filtering" (at the egress/downstream PE)
used in the split-horizon procedures. In [RFC7432] the Ethernet
Segment Identifier label indicates what egress Attachment Circuits
must be skipped when forwarding BUM traffic to the egress. In
this document, the Ethernet Segment Identifier label indicates
what ingress traffic must be discarded at the downstream PE.
The use of Ethernet Segment Identifier labels for Single Flow Groups
forwarded by upstream PEs require some control plane and data plane
extensions in the procedures used by [RFC7432] for multi-homing.
Upon failure of the selected G-source, the downstream PE will switch
over to a different selected G-source, and will therefore change the
Reverse Path Forwarding check for the (*,G) state. The extensions
and associated procedures are described in Section 3 and Section 5
respectively.
An operator should use the Hot Standby solution if they require a
fast fail-over time and the additional bandwidth consumption is
acceptable (Single Flow Group packets are received multiple times on
the downstream PEs). Otherwise the operator should use the Warm
Standby solution, at the expense of a slower fail-over time in case
of a G-source or upstream PE failure. Besides bandwidth efficiency,
another advantage of the Warm Standby solution is that only the
upstream PEs attached to the redundant G-sources for the same Single
Flow Group need to be upgraded to support the new procedures.
This document does not impose the support of both solutions on a
system. If one solution is supported, the support of the other
solution is OPTIONAL.
3. BGP EVPN Extensions
This document makes use of the following BGP EVPN extensions:
1. Single Flow Group flag in the Multicast Flags Extended Community
The Single Flow Group (SFG) flag is a new bit requested to IANA
out of the registry Multicast Flags Extended Community Flag
Values. This new flag is set for S-PMSI A-D routes that carry a
(*,G)/(S,G) Single Flow Group in the NLRI.
2. ESI Label Extended Community is used in S-PMSI A-D routes
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The Hot Standby solution requires the advertisement of one or
more ESI Label Extended Communities [RFC7432] that encode the
Ethernet Segment Identifier(s) associated to an S-PMSI A-D
(*,G)/(S,G) route that advertises the presence of a Single Flow
Group. Only the ESI Label value in the extended community is
relevant to the procedures in this document. The Flags field in
the extended community will be advertised as 0x00 and ignored on
reception. [RFC7432] specifies that the ESI Label Extended
Community is advertised along with the A-D per ES route. This
documents extends the use of this extended community so that it
can be advertised multiple times (with different ESI values)
along with the EVPN S-PMSI A-D route.
4. Warm Standby (WS) Solution for Redundant G-Sources
The general procedure is described as follows:
1. Configuration of the upstream PEs
Upstream PEs (possibly attached to redundant G-sources) need to
be configured to know which groups are carrying only flows from
redundant G-sources, that is, the Single Flow Groups (SFGs) in
the tenant domain. They will also be configured to know which
local Broadcast Domains may be attached to a redundant G-source.
The Single Flow Groups can be configured for any source, E.g.,
SFG for "*", or for a prefix that contains multiple sources that
will issue the same SFG, i.e., "10.0.0.0/30". In the latter case
sources 10.0.0.1 and 10.0.0.2 are considered as Redundant
G-sources, whereas 10.0.0.10 is not considered a redundant
G-source for the same SFG.
As an example (Figure 4):
* PE1 is configured to know that G1 is an SFG for any source and
redundant G-sources for G1 may be attached to Broadcast
Domains BD1 or BD2.
* Or PE1 can also be configured to know that G1 is an SFG for
the sources contained in 10.0.0.0/30, and those redundant
G-sources may be attached to Broadcast Domains BD1 or BD2.
2. Signaling the location of a G-source for a given Single Flow
Group
Upon receiving G-traffic for a configured SFG on a Broadcast
Domain, an upstream PE configured to follow this procedure, e.g.,
PE1:
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* Originates an S-PMSI A-D (*,G)/(S,G) route for the SFG. An
(*,G) route is advertised if the SFG is configured for any
source, and an (S,G) route is advertised (where the Source can
have any length) if the SFG is configured for a prefix.
* The S-PMSI A-D route is imported by all the PEs attached to
the tenant domain. In order to do that, the route will use
the SBD-RT (Supplementary Broadcast Domain Route Target) in
addition to the BD-RT (Broadcast Domain Route Target) of the
Broadcast Domain over which the G-traffic is received. The
route SHOULD also carry a Designated Forwarder Election
Extended Community and a flag indicating that it conveys an
SFG. The Designated Forwarder Election extended community and
its use is specified in [RFC8584].
* The above S-PMSI A-D route MAY be advertised with or without
PMSI Tunnel Attribute:
- With no PMSI Tunnel Attribute if an I-PMSI or S-PMSI A-D
with Ingress Replication, Assisted Replication or BIER are
to be used.
- With PMSI Tunnel Attribute in any other case.
* The S-PMSI A-D route is triggered by the first packet of the
SFG and withdrawn when the flow is not received anymore.
Detecting when the G-source is no longer active is a local
implementation matter. The use of a timer is RECOMMENDED.
The timer is started when the traffic to G1 is not received.
Upon expiration of the timer, the PE will withdraw the route.
3. Single Forwarder (SF) Election
If the PE with a local G-source receives one or more S-PMSI A-D
routes for the same Single Flow Group from a remote PE, it will
run a Single Forwarder Election based on the information encoded
in the Designated Forwarder Election extended community. Two
S-PMSI A-D routes are considered for the same SFG if they are
advertised for the same tenant, and their Multicast Source
Length, Multicast Source, Multicast Group Length and Multicast
Group fields match.
1. A given Designated Forwarder Algorithm can only be used if
all the PEs running the Algorithm have consistent input. For
example, in an OISM network, if the redundant G-sources for
an SFG are attached to Broadcast Domains with different
Ethernet Tags, the Default Designated Forwarder Election
Algorithm MUST NOT be used.
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2. In case the there is a mismatch in the Designated Forwarder
Election Algorithm or capabilities advertised by two PEs
competing for the Single Forwarder role, the lowest PE IP
address (given by the Originator Address in the S- PMSI A-D
route) will be used as a tie-breaker.
4. Reverse Path Forwarding check on the PEs attached to a redundant
G-source
All the PEs with a local G-source for the Single Flow Group will
add a Reverse Path Forwarding check to the (*,G)/(S,G) state for
the Single Flow Group. That Reverse Path Forwarding check
depends on the Single Forwarder Election result:
1. The non-Single Forwarder PEs discard any (*,G)/(S,G) packets
for the Single Flow Group received over a local Attachment
Circuit.
2. The Single Forwarder accepts any (*,G)/(S,G) packets for the
Single Flow Group it receives over one (and only one) local
Attachment Circuit.
The solution above provides redundancy for Single Flow Groups and it
does not require an upgrade of the downstream PEs (PEs where there is
certainty that no redundant G-sources are connected). Other
G-sources for non-Single Flow Groups may exist in the same tenant
domain. This document does not change the existing procedures for
non-Single Flow Group G-sources.
The redundant G-sources can be single-homed or multi-homed to a
Broadcast Domain in the tenant domain. Multi-homing does not change
the above procedures.
Section 4.1 and Section 4.2 show two examples of the Warm Standby
solution.
4.1. Warm Standby Example in an OISM Network
Figure 4 illustrates an example in which S1 and S2 are redundant
G-sources for the Single Flow Group (*,G1).
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S1 (Single S2
| Forwarder) |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
S-PMSI | +---+ | | +---+ | S-PMSI
(*,G1) | +---|BD1| | | +---|BD2| | (*,G1)
Pref200 | |VRF+---+ | | |VRF+---+ | Pref100
|SFG |+---+ | | | |+---+ | | SFG|
| +----|SBD|--+ | |-----------||SBD|--+ |---+ |
v | |+---+ | | |+---+ | | v
| +---------|--+ +------------+ |
SMET | | | SMET
(*,G1) | | (S1,G1) | (*,G1)
| +--------+------------------+ |
^ | | | | ^
| | | EVPN | | |
| | | OISM | | |
| | | | | |
PE3 | | PE4 | | PE5
+--------v---+ +------------+ | +------------+
| +---+ | | +---+ | | | +---+ |
| +---|SBD| |-------| +---|SBD| |--|---| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | |VRF+---+ |
|+---+ | | |+---+ | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | +--->|BD1|--+ |
|+---+ | |+---+ | |+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 4: WS Solution for Redundant G-Sources
The Warm Standby solution works as follows:
1. Configuration of the upstream PEs, PE1 and PE2
PE1 and PE2 are configured to know that G1 is an Single Flow
Group for any source and redundant G-sources for G1 may be
attached to Broadcast Domains BD1 or BD2, respectively.
2. Signaling the location of S1 and S2 for (*,G1)
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Upon receiving (S1,G1) traffic on a local Attachment Circuit, PE1
and PE2 originate S-PMSI A-D (*,G1) routes with the SBD-RT
(Supplementary Broadcast Domain Route Target), Designated
Forwarder Election Extended Community and a flag indicating that
it conveys a Single Flow Group.
3. Single Forwarder (SF) Election
Based on the Designated Forwarder Election extended community
content, PE1 and PE2 elect a Single Forwarder for (*,G1).
Assuming both PEs agree on e.g., Preference based Election as the
algorithm to use [I-D.ietf-bess-evpn-pref-df], and PE1 has a
higher preference, PE1 becomes the Single Forwarder for (*,G1).
4. Reverse Path Forwarding check on the PEs attached to a redundant
G-source
a. The non-Single Forwarder, PE2, discards any (*,G1) packets
received over a local Attachment Circuit.
b. The Single Forwarder, PE1 accepts (*,G1) packets it receives
over one (and only one) local Attachment Circuit.
The end result is that, upon receiving reports for (*,G1) or (S,G1),
the downstream PEs (PE3 and PE5) will issue SMET routes and will pull
the multicast Single Flow Group from PE1, and PE1 only. Upon a
failure on S1, the Attachment Circuit connected to source S1 or PE1
itself will trigger the S-PMSI A-D (*,G1) withdrawal from PE1 and PE2
will be promoted to Single Forwarder.
4.2. Warm Standby Example in a Single-BD Tenant Network
Figure 5 illustrates an example in which S1 and S2 are redundant
G-sources for the Single Flow Group (*,G1), however, now all the
G-sources and receivers are connected to the same Broadcast Domain
BD1 and there is no Supplementary Broadcast Domain.
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S1 (Single S2
| Forwarder) |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
S-PMSI | +---+ | | +---+ | S-PMSI
(*,G1) | |BD1| | | |BD1| | (*,G1)
Pref200 | +---+ | | +---+ | Pref100
|SFG | | | | | SFG|
| +---| | |-----------| |---+ |
v | | | | | | | v
| +---------|--+ +------------+ |
SMET | | | SMET
(*,G1) | | (S1,G1) | (*,G1)
| +--------+------------------------+ |
^ | | | | ^
| | | EVPN | | |
| | | | | |
| | | | | |
PE3 | | PE4 | | PE5
+--------v---+ +------------+ +-|----------+
| +---+ | | +---+ | | | +---+ |
| |BD1| |-------| |BD1| |------| +--->|BD1| |
| +---+ | | +---+ | | +---+ |
| | | | | |
| | | | | |
| | | | | |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 5: WS Solution for Redundant G-Sources in the same BD
The same procedure as in Section 4.1 is valid here, being this a sub-
case of the one in Section 4.1. Upon receiving traffic for the
Single Flow Group G1, PE1 and PE2 advertise the S-PMSI A-D routes
with route target BD1-RT only, since there is no Supplementary
Broadcast Domain (SBD).
5. Hot Standby (HS) Solution for Redundant G-Sources
If fast-failover is required upon the failure of a G-source or PE
attached to the G-source and the extra bandwidth consumption in the
tenant network is not an issue, the Hot Standby solution should be
used. The procedure is as follows:
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1. Configuration of the PEs
As in the Warm Standby case, the upstream PEs where redundant
G-sources may exist need to be configured to know which groups
(for any source or a prefix containing the intended sources) are
carrying only flows from redundant G-sources, that is, the Single
Flow Groups in the tenant domain.
In addition (and this is not done in Warm Standby mode), the
individual redundant G-sources for a Single Flow Group need to be
associated with an Ethernet Segment on the upstream PEs. This is
irrespective of the redundant G-source being multi-homed or
single-homed. Even for single-homed redundant G-sources the Hot
Standby procedure relies on the ESI labels for the Reverse Path
Forwarding check on downstream PEs. The term "S-ESI" is used in
this document to refer to an Ethernet Segment Identifier
associated to a redundant G-source.
Contrary to what is specified in the Warm Standby method (that is
transparent to the downstream PEs), the support of the Hot
Standby procedure is required not only on the upstream PEs but
also on all downstream PEs connected to the receivers in the
tenant network. The downstream PEs do not need to be configured
to know the connected Single Flow Groups or their Ethernet
Segment Identifiers, since they get that information from the
upstream PEs. The downstream PEs will locally select an Ethernet
Segment Identifier for a given Single Flow Group, and will
program a Reverse Path Forwarding check to the (*,G)/(S,G) state
for the Single Flow Group that will discard (*,G)/(S,G) packets
from the rest of the Ethernet Segment Identifiers. The selection
of the Ethernet Segment Identifier for the Single Flow Group is
based on local policy.
2. Signaling the location of a G-source for a given Single Flow
Group and its association to the local Ethernet Segments
Based on the configuration in step 1, an upstream PE configured
to follow the Hot Standby procedures:
a. Advertises an S-PMSI A-D (*,G)/(S,G) route per each
configured Single Flow Group. These routes need to be
imported by all the PEs of the tenant domain, therefore they
will carry the route targets BD-RT (the route target of the
Broadcast Domain) and SBD-RT (the route target of the
Supplementary Broadcast Domain, if the SBD exists). The
route also carries the ESI Label extended communities needed
to convey all the S-ESIs associated to the Single Flow Group
in the PE.
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b. The S-PMSI A-D route will convey a PMSI Tunnel Attribute in
the same cases as in the Warm Standby procedure.
c. The S-PMSI A-D (*,G)/(S,G) route is triggered by the
configuration of the Single Flow Group and not by the
reception of G-traffic.
3. Distribution of DCB (Domain-wide Common Block) ESI-labels and
G-source ES routes
An upstream PE advertises the corresponding EVPN ES route, A-D
per EVI and A-D per ES routes for the local S-ESIs.
a. ES routes are used for regular Designated Forwarder Election
for the S-ES. This document does not introduce any change in
the procedures related to the EVPN ES routes.
b. The EVPN A-D per EVI and A-D per ES routes MUST include the
route target SBD-RT since they have to be imported by all the
PEs in the tenant domain.
c. The EVPN A-D per ES routes convey the S-ESI labels that the
downstream PEs use to add the Reverse Path Forwarding check
for the (*,G)/(S,G) associated to the Single Flow Groups.
This Reverse Path Forwarding check requires that all the
packets for a given G-source are received with the same S-ESI
label value on the downstream PEs. For example, if two
redundant G-sources are multi-homed to PE1 and PE2 via S-ES-1
and S-ES-2, PE1 and PE2 MUST allocate the same ESI label "Lx"
for S-ES-1 and they MUST allocate the same ESI label "Ly" for
S-ES-2. In addition, Lx and Ly MUST be different. These ESI
labels are Domain-wide Common Block (DCB) labels and follow
the allocation procedures in
[I-D.ietf-bess-mvpn-evpn-aggregation-label].
4. Processing of EVPN A-D per ES/EVI routes and Reverse Path
Forwarding check on the downstream PEs
The EVPN A-D per ES/EVI routes are received and imported in all
the PEs in the tenant domain. The processing of the EVPN A-D per
ES/EVI routes on a given PE depends on its configuration:
a. The PEs attached to the same Broadcast Domain of the route
target BD-RT that is included in the EVPN A-D per ES/EVI
routes will process the routes as in [RFC7432] and [RFC8584].
If the receiving PE is attached to the same Ethernet Segment
as indicated in the route, [RFC7432] split-horizon procedures
will be followed and the Designated Forwarder Election
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candidate list may be modified as in [RFC8584] if the
Ethernet Segment supports the AC-DF (Attachment Circuit
influenced Designated Forwarder) capability.
b. The PEs that are not attached to the Broadcast Domain
identified by the route target BD-RT but are attached to the
Supplementary Broadcast Domain of the received route target
SBD-RT, will import the EVPN A-D per ES/EVI routes and use
them for redundant G-source mass withdrawal, as explained
later.
c. Upon importing EVPN A-D per ES routes corresponding to
different S-ESes, a PE MUST select a primary S-ES and add a
Reverse Path Forwarding check to the (*,G)/(S,G) state in the
Broadcast Domain or Supplementary Broadcast Domain. This
Reverse Path Forwarding check will discard all ingress
packets to (*,G)/(S,G) that are not received with the ESI-
label of the primary S-ES. The selection of the primary S-ES
is a matter of local policy.
5. G-traffic forwarding for redundant G-sources and fault detection
Assuming there is (*,G) or (S,G) state for the Single Flow Group
with Output Interface list entries associated to remote EVPN PEs,
upon receiving G-traffic on a S-ES, the upstream PE will add a
S-ESI label at the bottom of the stack before forwarding the
traffic to the remote EVPN PEs. This label is allocated from a
Domain-wide Common Block as described in step 3. If Point-to-
multipoint or BIER PMSIs are used, this is not adding any new
data path procedures on the upstream PEs (except that the ESI-
label is allocated from a Domain-wide Common Block as described
in [I-D.ietf-bess-mvpn-evpn-aggregation-label]). However, if
Ingress Replication or Assisted Replication are used, this
document extends the [RFC7432] procedures by pushing the S-ESI
labels not only on packets sent to the PEs that shared the ES but
also to the rest of the PEs in the tenant domain. This allows
the downstream PEs to receive all the multicast packets from the
redundant G-sources with a S-ESI label (irrespective of the PMSI
type and the local ESes), and discard any packet that conveys a
S-ESI label different from the primary S-ESI label (that is, the
label associated to the selected primary S-ES), as discussed in
step 4.
If the last EVPN A-D per EVI or the last EVPN A-D per ES route
for the primary S-ES is withdrawn, the downstream PE will
immediately select a new primary S-ES and will change the Reverse
Path Forwarding check. Note that if the S-ES is re-used for
multiple tenant domains by the upstream PEs, the withdrawal of
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all the EVPN A-D per-ES routes for a S-ES provides a mass
withdrawal capability that makes a downstream PE to change the
Reverse Path Forwarding check in all the tenant domains using the
same S-ES.
The withdrawal of the last EVPN S-PMSI A-D route for a given
(*,G)/(S,G) that represents a Single Flow Group SHOULD make the
downstream PE remove the S-ESI label based Reverse Path
Forwarding check on (*,G)/(S,G).
5.1. Extensions for the Advertisement of DCB Labels
Domain-wide Common Block Labels are specified in
[I-D.ietf-bess-mvpn-evpn-aggregation-label] and this document makes
use of them for the procedures described in Section 5.
[I-D.ietf-bess-mvpn-evpn-aggregation-label] assumes that Domain-wide
Common Block labels can only be used along with Multipoint-to-
Multipoint, Point-to-Multipoint, or BIER tunnels and that, if the
PMSI label is signaled as a Domain-wide Common Block label, then the
ESI label used for multi-homing is also a Domain-wide Common Block
label. This document extends the use of the Domain-wide Common Block
allocation for ESI labels so that:
a. Domain-wide Common Block allocated ESI labels MAY be used along
with Ingress Replication tunnels, and
b. Domain-wide Common Block allocated ESI labels MAY be used by PEs
that do not use Domain-wide Common Block allocated PMSI labels.
This control plane extension is indicated by adding the DCB-flag
(Domain-wide Common Block flag) or the Context Label Space ID
extended community to the EVPN A-D per ES route(s) advertised for the
S-ES. The DCB-flag is encoded in the ESI Label Extended Community as
follows:
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=0x01 | Flags(1 octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 | ESI Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: ESI Label Extended Community
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This document defines the bit 5 in the Flags octet of the ESI Label
Extended Community as the ESI-DCB-flag. When the ESI-DCB-flag is
set, it indicates that the ESI label is a Domain-wide Common Block
label.
A received ESI label is considered a Domain-wide Common Block label
if either of these two conditions is met:
a. The ESI label is encoded in an ESI Label Extended Community with
the ESI-DCB-flag set.
b. The ESI label is signaled from a PE that advertised a PMSI label
that is a Domain-wide Common Block label.
As in [I-D.ietf-bess-mvpn-evpn-aggregation-label] this document also
allows the use of context label space ID extended community. When
the context label space ID extended community is advertised along
with the ESI label in an EVPN A-D per ES route, the ESI label is from
a context label space identified by the Domain-wide Common Block
label in the Extended Community.
5.2. Use of BFD in the HS Solution
In addition to using the state of the EVPN A-D per EVI, EVPN A-D per
ES or S-PMSI A-D routes to modify the Reverse Path Forwarding check
on (*,G)/(S,G) as discussed in Section 5, Bidirectional Forwarding
Detection (BFD) protocol MAY be used to monitor the status of the
multipoint tunnels used to forward the Single Flow Group ppackets
from the redundant G-sources.
The BGP-BFD Attribute is advertised along with the S-PMSI A-D or
Inclusive Multicast Ethernet Tag routes (depending on whether
Inclusive PMSI or Selective PMSI trees are used) and the procedures
described in [I-D.ietf-bess-evpn-bfd] [I-D.ietf-mpls-p2mp-bfd] are
used to bootstrap multipoint BFD sessions on the downstream PEs.
5.3. Hot Standby Example in an OISM Network
Figure 7 illustrates the Hot Standby model in an Optimized Inter-
Subnet Multicast (OISM) network. Consider S1 and S2 are redundant
G-sources for the Single Flow Group (*,G1) in Broadcast Domain BD1
(any source using G1 is assumed to transmit an SFG). S1 and S2 are
(all-active) multi-homed to upstream PEs, PE1 and PE2. The receivers
are attached to downstream PEs, PE3 and PE5, in Broadcast Domains BD3
and BD1, respectively. S1 and S2 are assumed to be connected by a
Link Aggregation Group to the multi-homing PEs, and the multicast
traffic can use the link to either upstream PE. The diagram
illustrates how S1 sends the G-traffic to PE1 and PE1 forwards to the
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remote interested downstream PEs, whereas S2 sends to PE2 and PE2
forwards further. In this Hot Standby model, the interested
downstream PEs will get duplicate G-traffic from the two G-sources
for the same Single Flow Group. While the diagram shows that the two
flows are forwarded by different upstream PEs, the all-active multi-
homing procedures may cause that the two flows come from the same
upstream PE. Therefore, finding out the upstream PE for the flow is
not enough for the downstream PEs to program the required Reverse
Path Forwarding check to avoid duplicate packets on the receiver.
S1(ESI-1) S2(ESI-2)
| |
| +----------------------+
(S1,G1)| | (S2,G1)|
+----------------------+ |
PE1 | | PE2 | |
+--------v---+ +--------v---+
| +---+ | | +---+ | S-PMSI
S-PMSI | +---|BD1| | | +---|BD1| | (*,G1)
(*,G1) | |VRF+---+ | | |VRF+---+ | SFG
SFG |+---+ | | | |+---+ | | | ESI1,2
ESI1,2 +---||SBD|--+ | |-----------||SBD|--+ | |---+ |
| | |+---+ | | EVPN |+---+ | | | v
v | +---------|--+ OISM +---------|--+ |
| | | |
| | (S1,G1) | |
SMET | +---------+------------------+ | | SMET
(*,G1) | | | | | (*,G1)
^ | | +----------------------------+---+ | ^
| | | | (S2,G1) | | | |
| | | | | | | |
PE3 | | | PE4 | | | PE5
+-------v-v--+ +------------+ | | +------------+
| +---+ | | +---+ | | | | +---+ |
| +---|SBD| +-------| +---|SBD| |--|-|-| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | | |VRF+---+ |
|+---+ | | |+---+ | | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | | +->|BD1|--+ |
|+---+ | |+---+ | +--->+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 7: HS Solution for Multi-homed Redundant G-Sources in OISM
In this scenario, the Hot Standby solution works as follows:
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1. Configuration of the upstream PEs, PE1 and PE2
PE1 and PE2 are configured to know that G1 is a Single Flow Group
for any source (a source prefix length could have been configured
instead) and the redundant G-sources for G1 use S-ESIs ESI-1 and
ESI-2 respectively. Both Ethernet Segments are configured in
both PEs and their ESI value can be configured or auto-derived.
The ESI-label values are allocated from a Domain-wide Common
Block [I-D.ietf-bess-mvpn-evpn-aggregation-label] and are
configured either locally or by a centralized controller. We
assume ESI-1 is configured to use ESI-label-1 and ESI-2 to use
ESI-label-2.
The downstream PEs, PE3, PE4 and PE5 are configured to support
Hot Standby mode and select the G-source with e.g., lowest ESI
value.
2. PE1 and PE2 advertise S-PMSI A-D (*,G1) and EVPN ES, A-D per ES
and A-D per EVI routes
Based on the configuration of step 1, PE1 and PE2 advertise an
S-PMSI A-D (*,G1) route each. The route from each of the two PEs
will include TWO ESI Label Extended Communities with ESI-1 and
ESI-2 respectively, as well as route target BD1-RT plus SBD-RT
and a flag that indicates that (*,G1) is a Single Flow Group.
In addition, PE1 and PE2 advertise EVPN ES and A-D per ES/EVI
routes for ESI-1 and ESI-2. The EVPN A-D per ES and per EVI
routes will include the route target of the SBD, i.e.,: SBD-RT,
so that they can be imported by the downstream PEs that are not
attached to Broadcast Domain BD1, e.g., PE3 and PE4. The EVPN
A-D per ES routes will convey ESI-label-1 for ESI-1 (on both PEs)
and ESI-label-2 for ESI-2 (also on both PEs).
3. Processing of EVPN A-D per ES/EVI routes and Reverse Path
Forwarding check
PE1 and PE2 received each other's ES and A-D per ES/EVI routes.
Regular [RFC7432] [RFC8584] procedures will be followed for the
Designated Forwarder Election and programming of the ESI-labels
for egress split-horizon filtering. PE3/PE4 import the EVPN A-D
per ES/EVI routes in the SBD. Since PE3 has created a (*,G1)
state based on local interest, PE3 will add a Reverse Path
Forwarding check to (*,G1) so that packets coming with ESI-
label-2 are discarded (lowest ESI value is assumed to give the
primary S-ES).
4. G-traffic forwarding and fault detection
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PE1 receives G-traffic (S1,G1) on ES-1 that is forwarded within
the context of Broadcast Domain BD1. Irrespective of the tunnel
type, PE1 pushes ESI-label-1 at the bottom of the stack and the
traffic gets to PE3 and PE5 with the mentioned ESI-label (PE4 has
no local interested receivers). The G-traffic with ESI-label-1
passes the Reverse Path Forwarding check and it is forwarded to
R1. In the same way, PE2 sends (S2,G1) with ESI-label-2, but
this G-traffic does not pass the Reverse Path Forwarding check
and gets discarded at PE3/PE5.
If the link from S1 to PE1 fails, S1 will forward the (S1,G1)
traffic to PE2 instead. PE1 withdraws the EVPN ES and A-D routes
for ESI-1. Now both flows will be originated by PE2, however the
Reverse Path Forwarding checks do not change in PE3/PE5.
If subsequently, the link from S1 to PE2 fails, PE2 also
withdraws the EVPN ES and A-D routes for ESI-1. Since PE3 and
PE5 have no longer A-D per ES/EVI routes for ESI-1, they
immediately change the Reverse Path Forwarding check so that
packets with ESI-label-2 are now accepted.
Figure 8 illustrates a scenario where sources S1 and S2 are single-
homed to PE1 and PE2 respectively. This scenario is a sub-case of
the one in Figure 7. Now ES-1 only exists in PE1, hence only PE1
advertises the EVPN A-D per ES/EVI routes for ESI-1. Similarly, ES-2
only exists in PE2 and PE2 is the only PE advertising EVPN A-D routes
for ESI-2. The same procedures as in Figure 7 apply to this use-
case.
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S1(ESI-1) S2(ESI-2)
| |
(S1,G1)| (S2,G1)|
| |
PE1 | PE2 |
+--------v---+ +--------v---+
| +---+ | | +---+ | S-PMSI
S-PMSI | +---|BD1| | | +---|BD2| | (*,G1)
(*,G1) | |VRF+---+ | | |VRF+---+ | SFG
SFG |+---+ | | | |+---+ | | | ESI2
ESI1 +---||SBD|--+ | |-----------||SBD|--+ | |---+ |
| | |+---+ | | EVPN |+---+ | | | v
v | +---------|--+ OISM +---------|--+ |
| | | |
| | (S1,G1) | |
SMET | +---------+------------------+ | | SMET
(*,G1) | | | | | (*,G1)
^ | | +--------------------------------+----+ | ^
| | | | (S2,G1) | | | |
| | | | | | | |
PE3 | | | PE4 | | | PE5
+-------v-v--+ +------------+ | +------v-----+
| +---+ | | +---+ | | | +---+ |
| +---|SBD| |-------| +---|SBD| |--|---| +---|SBD| |
| |VRF+---+ | | |VRF+---+ | | | |VRF+---+ |
|+---+ | | |+---+ | | | |+---+ | |
||BD3|--+ | ||BD4|--+ | +--->|BD1|--+ |
|+---+ | |+---+ | |+---+ |
+------------+ +------------+ +------------+
| ^ | ^
| | IGMP | | IGMP
R1 | J(*,G1) R3 | J(*,G1)
Figure 8: HS Solution for single-homed Redundant G-Sources in OISM
5.4. Hot Standby Example in a Single-BD Tenant Network
Irrespective of the redundant G-sources being multi-homed or single-
homed, if the tenant network has only one Broadcast Domain, e.g.,
BD1, the procedures of Section 5.2 still apply, only that routes do
not include any SBD route target, i.e.,: SBD-RT, and all the
procedures apply to Broadcast Domain BD1 only.
6. Security Considerations
The same Security Considerations described in
[I-D.ietf-bess-evpn-irb-mcast] are valid for this document.
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From a security perspective, out of the two methods described in this
document, the Warm Standby method is considered lighter in terms of
control plane and therefore its impact is low on the processing
capabilities of the PEs. The Hot Standby method adds more burden on
the control plane of all the PEs of the tenant with sources and
receivers.
7. IANA Considerations
IANA is requested to allocate a Bit in the Multicast Flags Extended
Community to indicate that a given (*,G) or (S,G) in an S-PMSI A-D
route is associated with an SFG (Single Flow Group).
8. References
8.1. Normative References
[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>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[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>.
[RFC9251] Sajassi, A., Thoria, S., Mishra, M., Patel, K., Drake, J.,
and W. Lin, "Internet Group Management Protocol (IGMP) and
Multicast Listener Discovery (MLD) Proxies for Ethernet
VPN (EVPN)", RFC 9251, DOI 10.17487/RFC9251, June 2022,
<https://www.rfc-editor.org/info/rfc9251>.
[I-D.ietf-bess-evpn-irb-mcast]
Lin, W., Zhang, Z. J., Drake, J., Rosen, E. C., Rabadan,
J., and A. Sajassi, "EVPN Optimized Inter-Subnet Multicast
(OISM) Forwarding", Work in Progress, Internet-Draft,
draft-ietf-bess-evpn-irb-mcast-09, 21 February 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-irb-mcast-09>.
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[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
VPN Designated Forwarder Election Extensibility",
RFC 8584, DOI 10.17487/RFC8584, April 2019,
<https://www.rfc-editor.org/info/rfc8584>.
[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>.
[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>.
[I-D.ietf-bess-mvpn-evpn-aggregation-label]
Zhang, Z. J., Rosen, E. C., Lin, W., Li, Z., and I.
Wijnands, "MVPN/EVPN Tunnel Aggregation with Common
Labels", Work in Progress, Internet-Draft, draft-ietf-
bess-mvpn-evpn-aggregation-label-09, 12 December 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
mvpn-evpn-aggregation-label-09>.
8.2. Informative References
[RFC9136] Rabadan, J., Ed., Henderickx, W., Drake, J., Lin, W., and
A. Sajassi, "IP Prefix Advertisement in Ethernet VPN
(EVPN)", RFC 9136, DOI 10.17487/RFC9136, October 2021,
<https://www.rfc-editor.org/info/rfc9136>.
[I-D.ietf-bess-evpn-bum-procedure-updates]
Zhang, Z. J., Lin, W., Rabadan, J., Patel, K., and A.
Sajassi, "Updates on EVPN BUM Procedures", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-bum-
procedure-updates-14, 18 November 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-bum-procedure-updates-14>.
[I-D.ietf-bess-evpn-pref-df]
Rabadan, J., Sathappan, S., Lin, W., Drake, J., and A.
Sajassi, "Preference-based EVPN DF Election", Work in
Progress, Internet-Draft, draft-ietf-bess-evpn-pref-df-10,
2 September 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-bess-evpn-pref-df-10>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
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[I-D.ietf-bess-evpn-bfd]
Govindan, V. P., Mudigonda, M., Sajassi, A., Mirsky, G.,
and D. E. Eastlake, "EVPN Network Layer Fault Management",
Work in Progress, Internet-Draft, draft-ietf-bess-evpn-
bfd-04, 8 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-bfd-04>.
[I-D.ietf-mpls-p2mp-bfd]
Mirsky, G., Mishra, G. S., and D. E. Eastlake, "BFD for
Multipoint Networks over Point-to-Multi-Point MPLS LSP",
Work in Progress, Internet-Draft, draft-ietf-mpls-p2mp-
bfd-05, 19 June 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
p2mp-bfd-05>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
Appendix A. Acknowledgments
The authors would like to thank Mankamana Mishra, Ali Sajassi and
Greg Mirsky for their review and valuable comments.
Appendix B. Contributors
Authors' Addresses
Jorge Rabadan (editor)
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085
United States of America
Email: jorge.rabadan@nokia.com
Jayant Kotalwar
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085 USA
Email: jayant.kotalwar@nokia.com
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Senthil Sathappan
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085 USA
Email: senthil.sathappan@nokia.com
Zhaohui Zhang
Juniper Networks
Email: zzhang@juniper.net
Wen Lin
Juniper Networks
Email: wlin@juniper.net
Eric C. Rosen
Individual
Email: erosen52@gmail.com
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