Internet DRAFT - draft-wang-bess-mvpn-upstream-df-selection
draft-wang-bess-mvpn-upstream-df-selection
Network Working Group F. Duan
Internet-Draft S. Chen
Intended status: Standards Track Huawei Technologies
Expires: 24 May 2024 Y. Liu
China Mobile
H. Wang
Ruijie Networks Co., Ltd.
21 November 2023
Multicast VPN Upstream Designated Forwarder Selection
draft-wang-bess-mvpn-upstream-df-selection-08
Abstract
This document defines Multicast Virtual Private Network (VPN)
extensions and procedures of designated forwarder election performed
between ingress PEs, which is different from the one described in
[RFC9026] in which the upstream designated forwarder determined by
using the "Standby PE Community" carried in the C-Multicast routes.
Based on the DF election, the failure detection point discovery
mechanism between DF and standby DF is extended in MVPN procedures to
achieve fast failover by using BFD session to track the status of
detection point. To realize a stable "warm root standby", this
document obsolete the P-Tunnel status determining procedure for
downstream PEs in regular MVPN by introducing a RPF Set Checking
mechanism as an instead.
Requirements Language
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.
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/.
Duan, et al. Expires 24 May 2024 [Page 1]
Internet-Draft MVPN Upstream DF Selection November 2023
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."
This Internet-Draft will expire on 24 May 2024.
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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scenario . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Passive IDF Negotiation Mode . . . . . . . . . . . . . . 5
3.2. Active IDF Negotiation Mode . . . . . . . . . . . . . . . 6
4. Specification . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. IDF Negotiation Community . . . . . . . . . . . . . . . . 6
4.2. BFD Discriminator Attribute . . . . . . . . . . . . . . . 7
5. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Signaling . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1.1. Originating VPN Routes to Multicast Sources . . . . . 7
5.1.2. Originating C-Multicast Routes . . . . . . . . . . . 8
5.1.3. Ingress Designated Forwarder Selection . . . . . . . 8
5.1.4. Failure Detection and Fast Failover . . . . . . . . . 10
5.2. Data Forwarding . . . . . . . . . . . . . . . . . . . . . 12
5.2.1. Procedure on Root PEs . . . . . . . . . . . . . . . . 12
5.2.2. Procedure on Leaf PEs . . . . . . . . . . . . . . . . 12
5.3. Distinguishing UMH and C-multicast Routes . . . . . . . . 12
5.4. Segmented Inter-AS Scenario . . . . . . . . . . . . . . . 14
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 15
6.1. Root PE Not Support IDF Election . . . . . . . . . . . . 15
6.2. Leaf PE Not Support IDF Election . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
Duan, et al. Expires 24 May 2024 [Page 2]
Internet-Draft MVPN Upstream DF Selection November 2023
10. Normative References . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
MVPN [RFC6513] and [RFC6514] defines the MVPN architecture and MVPN
protocol specification which include the basic procedures for
selecting the Upstream Multicast Hop. Further [RFC9026] defines some
extensions to select the primary and standby upstream PE for a VPN
multicast flow on downstream PEs. After selecting the Upstream
Multicast Hop, the downstream PEs send MVPN C-Multicast routes to
both primary and standby Upstream PE. Upon receiving the MVPN join
routes, the upstream / ingress PEs can either perform "hot root
standby" or "warm root standby". For the "hot root standby"
mechanism, all the ingress PEs, regardless of the primary or standby
role, forward (C-S,C-G) flow to other PEs through a P-tunnel, forcing
the egress PEs to discard all but one. In this way, the failover can
be conducted by leaf PE within extremely short duration when the
failure of upstream link or device is detected. However, this will
cause the steady traffic redundancy throughout the backbone network.
In the scenario where bandwidth waste issue is concerned, such as
enterprise networks crossing provider networks, the "warm root
standby" mechanism is expected to be a better solution. However,
there are some problems when deploying the "warm root standby"
mechanism described in [RFC9026].
a. Upon the failure of primary ingress PE, the leaf PE needs to send
the new C-multicast route towards the standby ingress PE without
carrying the Standby PE BGP Community according to [RFC9026].
Leaf PE needs to update all relevant C-multicast routes and sends
them to the standby ingress PE. For example, if there are 1000
(C-S,C-G)s, 1000 C-multicast routes will be updated and resent so
that the standby PE can finally forward traffic. The failover
time can hardly reach the same level of "hot root standby"
mechanism.
b. There is no endogenous mechanism for standby ingress PEs to
discover and detect the failure of primary ingress PEs, resulting
in the uncertainty in deployment and implementation. If the
standby ingress PE can directly detect the failure of the primary
ingress PE, it can take over the role of designated forwarder and
send the traffic immediately.
c. In [RFC9026], the standby ingress PE is determined by using
"Standby PE Community" carried in the C-Multicast routes. The
premise of this mechanism is that all leaf PEs choose the same
primary and standby ingress PEs, which may not be met due to
transient unicast routing inconsistencies, the inconsistencies of
Duan, et al. Expires 24 May 2024 [Page 3]
Internet-Draft MVPN Upstream DF Selection November 2023
P-Tunnel status determined by each leaf PE or lack of support of
the Standby PE community on leaf PE, causing that the "warm root
standby" mechanism is not stable and returns to "hot root
standby" mode because the standby ingress PE also sends multicast
traffic to backbone when the condition is not satisfied.
d. When the primary and standby designated forwarders are selected
based on IP addresses of root PEs, the primary and standby roles
are fixed for each multicast flow. Ingress PEs cannot perform
load balancing for different multicast traffic. Hashing
algorithm in [RFC6513] utilized source and group addresses and
allows load balancing for different (C-S,C-G)s. However, the
specific procedure of selecting a standby PE was not specified.
The hot root standby is good at fast failover. The warm root standby
has advantages of saving the bandwidth. In order to have both
advantages of hot root standby and warm root standby, this document
defines a new MVPN procedure of designated forwarder election
performed between ingress PEs. Based on the DF election, the failure
detection point discovery mechanism between DF and standby DF is
extended to achieve fast failover by using a BFD session to track the
status of detection point. To realize a stable "warm root standby",
this document obsoletes the P-Tunnel status determining procedure for
downstream PEs in regular MVPN by introducing a RPF Set Checking
mechanism as an instead.
2. Terminology
The terminology used in this document is the terminology defined
in[RFC6513], [RFC6514] and [RFC9026].
For convenience of description, the abbreviations used in this
document is listed below.
DF: Designated Forwarder
IDF: Ingress Designated Forwarder
UMH: Upstream Multicast Hop
P-tunnel: Provider-Tunnel
VPN: Virtual Private Network
MVPN: Multicast VPN
GTM: Global Table Multicast
Duan, et al. Expires 24 May 2024 [Page 4]
Internet-Draft MVPN Upstream DF Selection November 2023
RD: Route Distinguisher
NLRI: Network Layer Reachability Information
BFD: Bidirectional Forwarding Detection
MD: My Discriminator
VRI: VRF Route Import Extended Community
RR: Route Reflector
SFS: Selective Forwarder Selection
PTA: PMSI Tunnel Attribute
A new term is introduced below.
RPF Set Checking: RPF Set is a set of valid upstream interfaces
that can accept multicast traffic. RPF Set checking allows
multicast traffic to be received from backup P-Tunnel quickly when
failure occurs.
3. Scenario
3.1. Passive IDF Negotiation Mode
+------------------------+
| |
/ Root PE1 Leaf PE1 ----- R1
/ | |
S1 --- CE | Provider Backbone |
\ | |
\ Root PE2 Leaf PE2 ----- R2
| |
+------------------------+
Figure 1: Passive IDF Negotiation Mode
In this scenario, the interfaces multihoming CE to provider's root
PEs are bundled together and working in a eth-trunk mode, and a
multichassis protocol is running between the multi-homed root PEs to
coordinate with the CE to perform single active or all active data
sending mode between CE and root PEs. Regardless either of the two
sending mode is chosen, CE received multicast data from S1 only
selects one interface to forward traffic, thus the root PE homed by
Duan, et al. Expires 24 May 2024 [Page 5]
Internet-Draft MVPN Upstream DF Selection November 2023
the selected interface is responsible for sending the corresponding
multicast traffic to leaf PEs. The multi-homed root PEs do not
really run an IDF negotiation procedure between themselves but accept
the IDF role passively. Therefore, we call this scenario using
Passive IDF Negotiation Mode in this document.
3.2. Active IDF Negotiation Mode
+------------------------+
+----------------+ | |
| | -- Root PE1 Leaf PE1 ----- R1
| | | |
S1 --- | Client Network | | Provider Backbone |
| | | |
| | -- Root PE2 Leaf PE2 ----- R2
+----------------+ | |
+------------------------+
Figure 2: Active IDF Negotiation Mode
In this scenario, the "Client Network" is a layer 3 network area
containing one or more CE routers. If only one CE router is included
in the "Client Network" , the main difference between this
circumstance and above is that the interfaces multihoming CE to root
PEs are not bundled and each of them is an individual layer 3
interface. The IP subnet of the multihoming interfaces can be in
either same or different, each of the multi-homed root PEs can
receive one copy of the specific multicast stream (S1, G) received
through the "Client Network". For the "warm root standby" mechanism,
only one root PE (Called IDF in this document) can send the received
multicast traffic to leaf PEs through provider's backbone. Thus the
IDF must be selected among the multi-homed root PEs by themselves.
So, in this document, we call this scenario using Active IDF
Negotiation Mode.
4. Specification
4.1. IDF Negotiation Community
This community is carried in the UMH routes and used by the multi-
homed root PEs to notify each other to perform IDF election. Leaf
PEs can also check whether the UMH route is containing this community
to perform checking according to the RPF Set Checklist. The value of
this community will be allocated by IANA for each negotiation mode
individually from the "Border Gateway Protocol (BGP) Well-known
Communities" registry using the First Come First Served registration
policy.
Duan, et al. Expires 24 May 2024 [Page 6]
Internet-Draft MVPN Upstream DF Selection November 2023
4.2. BFD Discriminator Attribute
This attribute is carried in UMH routes and its format reuses the one
defined in [RFC9026] with the "BFD Mode" field redefined as a unicast
BFD session type, of which the value is recommended to be 2 and will
be allocated by IANA according to the registration policy. The
source IP optional TLV in this document is mandatory and used to
discover the failure detection point of the IDF.
5. Procedure
5.1. Signaling
In this section, the procedure is under the condition that the value
of the RDs of multi-homed root PEs for a same MVPN are distinct,
which means that the VPN route originated by each multi-homed PE can
be received by the others and leaf PEs can also perform SFS reliably.
5.1.1. Originating VPN Routes to Multicast Sources
To perform IDF election procedure in this document, the multi-homed
root PEs MUST include an IDF negotiation Community in the originating
VPN routes to multicast sources. The negotiation mode (Passive or
Active) is determined by the connection type of the Client network /
CE, and MUST be configured consistently on each multi-homed root PE.
In order to perform endogenous mechanism of IDF election and fast
failure detection, the BFD Discriminator Attribute described in
section 4.2 MUST also be carried when each multi-homed root PE
originates a UMH routes, with the MD field filled with a local
configured BFD discriminator and the IP address field of the Source
IP TLV filled with the local IP of the interface connecting to the
Client network / CE, from which the prefix of the originating UMH
route is learned. If the UMH prefix is learned from more than one
local interface, the one chosen to fill the Source IP TLV of the BFD
Discriminator Attribute MUST be consistent with the one selected as
RPF interface for the multicast stream sent by the corresponding
multicast source. In this document, the filled Source IP address is
the failure detection point, if the corresponding root PE is selected
as the IDF of a specific multicast stream, it is used to establish a
BFD session to do fast tracking of failure of IDF. In IPv6
scenarios, a global IPv6 address SHOULD be configured on the client
facing interfaces to succeed in the establishment of multi-hop IPv6
BFD sessions.
Duan, et al. Expires 24 May 2024 [Page 7]
Internet-Draft MVPN Upstream DF Selection November 2023
5.1.2. Originating C-Multicast Routes
If a leaf PE decides to send C-Multicast routes to upstream PEs for a
given (C-S,C-G), it follows the procedure described in [RFC6514]
excepting that the RPF route of the c-root has an IDF negotiation
community. According to the negotiation community, a distinct
C-Multicast route for (C-S,C-G) is sent to each multi-homed root PE.
Leaf PE installs all P-Tunnels rooted from the multi-homed PEs into
the RPF tunnel checklist of the corresponding multicast traffic
(C-S,C-G).
If there is a local receiver connected to one of the multi-homed root
PEs and the Passive IDF Negotiation Mode is performed between them,
the root PE having local receivers sends the specific C-Multicast
route (C-S,C-G) joined by the local receivers to the multi-homed
others, after which it installs all P-Tunnels rooted from the multi-
homed others and local upstream interface into the RPF tunnel
checklist of the corresponding multicast traffic (C-S,C-G).
5.1.3. Ingress Designated Forwarder Selection
For Passive IDF election, it is performed by CE routers as described
in section 3.1. This section describes two optional solutions for
Active IDF election.
5.1.3.1. Out-Of-Band Mechanism
VRRP specifies an election protocol that dynamically assigns
responsibility of a virtual router to one of the VRRP routers on a
LAN. The VRRP router controlling the IPv4 or IPv6 address(es)
associated with a virtual router is called the Master, and it
forwards packets sent to these IPv4 or IPv6 addresses. Similarly,
the role of the VRRP routers associated with a virtual router can
also be that of the upstream PEs in MVPN dual homing upstream PEs
deployment.
The method of mapping the role of a VRRP router to that of a MVPN
upstream PE is more likely an administrative measure and could be
implemented as configurable policies. Both the primary and standby
PEs install VRF PIM state corresponding to BGP Source Tree Join route
and send C-Join messages to the CE toward C-S. Whereas only the
primary upstream PE (Virtual Router Master according to VRRP)
forwards (C-S,C-G) flow to downstream PEs through a P-tunnel if IDF
election is performing between the upstream PEs.
Duan, et al. Expires 24 May 2024 [Page 8]
Internet-Draft MVPN Upstream DF Selection November 2023
Other private implementations or similar designated forwarder
selection technologies could also be optional. However, a feasible
technology should has the ability to be deployed per VRF and be
associated with one Multicast VPN instance. All PEs connected to the
same customer's layer 3 network area MUST keep a coincident status of
whether performing IDF election or not by negotiating dynamically or
being configured manually, the dynamic protocol for negotiation of
this status is outside the scope of this document.
5.1.3.2. Endogenous Mechanism
Considering a multicast source connecting to the client network area
multihoming to the provider network, the prefix of the source can be
learned by all multi-homed root PEs, each of which originates a
corresponding VPN route with a VRI Extended Community including the
originator's IP address to the others and leaf PEs. According to
that, each multi-homed root PE can learn all the others' originator
IP addresses for a specific multicast source, based on which the IDF
can be calculated consistently on each root.
The default procedure for IDF election is at the granularity of
(C-S,C-G). There are two options listed below for IDF election of a
specific multicast source C-S, a deployment can use each of them and
MUST be configured consistently among the multi-homed root PEs:
a. To perform single IDF election for all C-Gs of a specific
multicast source C-S, each PE builds an ordered list in ascending
order of the IP addresses of all multi-homed PE nodes learning
the UMH routes to the multicast source C-S (including itself).
As described in the first paragraph of this section, each IP
address in this list is extracted from the Global Administrator
field of VRI Extended Community carried in those UMH routes
related to the specified multicast source C-S. Every PE is then
given an ordinal indicating its position in the ordered list,
starting with 0 as the ordinal for the PE with the numerically
lowest IP address. The originator IP address with ordinal 0 is
the winner, and the corresponding root PE is selected as IDF by
every PE. The root PE of which the corresponding originator IP
address is sub-optimal is selected as Standby IDF.
b. To perform IDF election for each C-G of a specific multicast
source C-S, each PE also builds an ordered list of the IP
addresses of all the multi-homed PE nodes at first. The
difference between this option and above is that the election of
IDF occurs not upon receiving all UMH routes of the other multi-
homed PEs of the specified C-S but upon receiving the C-multicast
join of the corresponding C-G. Assuming an ordered list of N
elements, the PE with ordinal i is the IDF for a C-G when (C-G
Duan, et al. Expires 24 May 2024 [Page 9]
Internet-Draft MVPN Upstream DF Selection November 2023
mod N) = i. The PE with ordinal j is the Standby IDF when j is
(C-G mod (N-1)). The calculation of standby IDF uses the ordered
IP addresses list without considering the existence of the
elected IDF element.
In order to reduce traffic waste between the Client Network and root
PEs, a root PE can only send C-PIM Join messages towards the Client
Network if it is the primary or standby DF.
5.1.4. Failure Detection and Fast Failover
For the Passive IDF Negotiation Mode, the CE router is responsible
for the failure detection of multihoming links or multi-homed PE
nodes using some existing solution, which is out the scope of this
document. For the Active IDF Negotiation Mode with Out-Of-Band
Mechanism described in section 5.1.3.1, the failure detection
solution is always built in the multichassis protocols used for IDF
election. This section only details the failure detection and fast
failover procedure for the Active IDF negotiation mode with
endogenous mechanism. Two methods are proposed to detect the
failure.
5.1.4.1. BFD Method
To detect the failure of the node or the client facing link of IDF
quickly, after the election of IDF PE and Standby IDF PE, the Standby
IDF initializes a BFD session. Several important parameters of the
BFD session are introduced as follows. The source IP of the BFD
session uses a local configured IP address of the corresponding
multicast VRF. The destination IP is extracted from the Source IP
TLV of BFD Discriminator Attribute carried in the UMH route sent by
the IDF. MD is filled with the MD field of BFD Discriminator
Attribute carried in VPN routes originated by current Standby IDF.
The YD(Your Discriminator) of the BFD session is dynamically learned
through the BFD initialization procedure.
Upon the occasion of the failure, the status of the BFD session goes
down. The Standby IDF PE of the C-Gs selecting the failure /
affected node as IDF takes over the primary role and sends the
multicast traffic belonging to C-Gs to leaf PEs through the backbone.
The failure / affected PE withdraws its VPN route advertised before,
this will re-trigger the procedure described in section 5.1.3.2 and a
new IDF PE (which was the old Standby IDF PE) and Standby IDF PE will
be selected. The new standby IDF MUST send C-PIM Join message
towards Client Network to receive multicast traffic.
Duan, et al. Expires 24 May 2024 [Page 10]
Internet-Draft MVPN Upstream DF Selection November 2023
If the previous failure node / link goes up again or a new multi-
homed PE of the specified multicast source is coming up and the IDF
PE is calculated to be changed, the new IDF will take over the
running IDF. To avoid data transfer crash, the running IDF (That
should be the new Standby IDF) does not trigger the establishment of
BFD session with new IDF until the local configured failback time
expires, during which it keeps the IDF role and waits the new IDF
completing the establishment of the multicast path from the SDR of
the specified multicast source to itself. Upon the occasion of BFD
session goes up, the running IDF stops sending multicast traffic to
leaf PEs and the new IDF takes over the IDF role to send multicast
stream for (C-S,C-G).
5.1.4.2. Monitoring traffic from IDF
The second method needs standby IDF to detect the failure by joining
a P-Tunnel rooted at the IDF and monitoring the traffic received from
the P-Tunnel. Even though there may be no local receiver connected
to the standby IDF, the standby IDF needs to join the P-Tunnel by
sending Leaf A-D Route or P-Tree Signaling. Standby IDF then sends
the C-Multicast Route to IDF in order to receive traffic from the
P-Tunnel. IDF will receive traffic from the IDF and the client
facing interface simultaneously. However, it does not forward
traffic to leaf PE when failure is not detected. When failures occur
between the client network and IDF, the standby IDF will no longer
receive any traffic from the P-Tunnel. The detection of interrupted
flow will trigger the role transition from standby IDF to IDF. Then
the new IDF will forward traffic to leaf PE.
However, the standby IDF may also cannot receive traffic when the
failure occurs between the IDF and standby IDF. Under this
circumstance, the standby IDF will switch to IDF when the client
facing link and IDF still work well. There will be dual IDFs and
leaf PE will receive two copies of the same flow. Suggestions about
deployment are provided to avoid this situation:
a. Multiple parallel links are suggested to be deployed between the
IDF and standby IDF. The probability of dual IDFs due to link
failure can be greatly reduced.
b. PMSI tunnel protection can be utilized together. When the link
between IDF and standby IDF fails, the underlay local protection
of PMSI Tunnel can ensure that standby IDF can still receive
traffic from IDF and avoid the dual-IDF situation.
Duan, et al. Expires 24 May 2024 [Page 11]
Internet-Draft MVPN Upstream DF Selection November 2023
5.2. Data Forwarding
5.2.1. Procedure on Root PEs
For the Passive IDF Negotiation Mode, the set of leaves of P-Tunnel
rooted at each multi-homed PE has the others as members if the others
have local receivers willing to accept the corresponding C-Flow. The
detailed signaling procedure is described in section 5.1.2. When CE
sends multicast data performing load balance to only one root PE
(Which is the Passive IDF), IDF send this multicast traffic to the
leaf PEs and the other multi-homed root PEs. When the multi-homed
root PEs receive the C-Flow, it MUST perform RPF Set Checking, by
accepting the data from either the client facing interface learning
the corresponding route of the multicast source or anyone of the
P-Tunnels rooted at the other multi-homed PEs. To avoid multicast
traffic loop and duplication, the data received from the P-Tunnels at
each root PE MUST NOT send back to P-Tunnels again and can only be
forwarded to the local receivers of the receiving PE.
For the Active IDF Negotiation Mode, each multi-homed root PE
receives a copy of C-Flow and forwards the multicast traffic to its
local receivers. Only DF can send data to leaf PEs through backbone.
All of the multi-homed root PEs perform RPF Set checking by matching
their client facing interface exactly.
5.2.2. Procedure on Leaf PEs
For either of the two IDF negotiation modes described in this
document, leaf PEs install each P-Tunnel rooted at each multi-homed
root PE into the RPF Set checklist for the corresponding multicast
flow (C-S,C-G), thus the multicast data sent by each of the multi-
homed root PEs can be accepted by leaf PEs. Upon the failure of IDF,
the Standby IDF takes over the primary role and leaf PEs are ready to
receive the data sent by the new primary IDF with no latency thanks
to the RPF Set checking mechanism.
5.3. Distinguishing UMH and C-multicast Routes
It was recommended in RFC 6514, on each multi-homed root PE, the UMH
VRF of the MVPN MUST use its own distinct RD to support non-congruent
unicast and multicast connectivity, the procedure described in above
section is also under this premise. However, in [RFC7716], the UMH
routes are not sent in the VPN-IP SAFI and there is no RD included in
the NLRI key. There are also some other scenarios that the UMH VRF
of the MVPN on the multi-homed PEs MUST be configured with a same RD
for some deployment reasons, which causing that the IDF negotiation
procedure can hardly be performed because that the UMH route
originated by each multi-homed root PE cannot be collected reliably
Duan, et al. Expires 24 May 2024 [Page 12]
Internet-Draft MVPN Upstream DF Selection November 2023
by the other root PEs and leaf PEs because of the route selecting
mechanism on BGP RRs. When UMH routes to same multicast source from
different root PEs carry same RD or no RD, they will be same from the
perspective of leaf PEs. Because Originating Router's IP Address is
not the key field when the UMH route is processed.
For the scenarios of the same RD, this document introduces a new type
of UMH route to be sent in MVPN SAFI, of which the NLRI key consists
of the following fields:
+------------------------------------------------+
| RD (8 octets) |
+------------------------------------------------+
| IP Prefix Length (1 octet, 0 to 32 / 128) |
+------------------------------------------------+
| IP Prefix (4 / 16 octets ) |
+------------------------------------------------+
| Originating Router's IP Addr (4 / 16 octets) |
+------------------------------------------------+
Figure 3: MVPN UMH Routes
The length of the IP Prefix field is determined by the address family
of MVPN. If IPv4 is being used, it will be 4 octets. Otherwise it
will be 16 octets for IPv6. After determining the length of IP
Prefix field, the length of the Originating Router's IP Addr field is
judged by NLRI key length. The type of this route will be allocated
in IANA.
If the RDs of the UMH VRFs on the multi-homed root PEs are same, the
root PEs import the routes of the client multicast sources to their
local UMH VRFs and send above UMH routes to all other PEs of the
MVPN. The UMH routes will carry a VRI Extended Community described
in [RFC6514], an IDF negotiation Community and a BFD Discriminator
Attribute described in this document. All the procedure applied to
the VPN-IP routes described in [RFC6513] and [RFC6514] SHOULD be
inherited by this UMH route. The receivers (which should be MVPN
PEs) of this route MUST install it into their local multicast RIB as
UMH route and it has a higher priority than other existing UMH route
type while a MVPN PE using it to determine the upstream PE of a
specified (C-S,C-G) or (C-*,C-G). The Originating Router's IP Addr
will be used to identify UMH routes from different upstream PEs.
For the non-segmented Inter-AS P-Tunnel over IPv6 infrastructure
scenarios, the length of Source AS field of C-Multicast routes cannot
hold an IPv6 address, causing that it is hard to distinguish the two
C-Multicast routes with a same granularity of (C-S,C-G) or (C-*,C-G)
Duan, et al. Expires 24 May 2024 [Page 13]
Internet-Draft MVPN Upstream DF Selection November 2023
sent to two ingress PEs individually. To solve this problem, this
document introduces a Root Distinguisher Extended Community, which is
an IP-address-specific Extended Community with a fixed type of IPv4.
The Global Administrator field of this Extended Community is filled
with a 4-octet global unique value configured. This 4-octet value
and the IPv6 Originating Router's IP Addresses of each MVPN PE needs
not to be a routable IPv4 address. The Local Administrator field of
the Extended Community is filled with 0. The type and sub type of
this Extended Community will be allocated in IANA.
The Root Distinguishing Extended Community is carried in the Intra-AS
AD routes or the wildcard S-PMSI AD routes. According to [RFC6514]
and [RFC6515], the non-segmented Inter-AS and IPv6 infrastructure
scenarios are determined on MVPN leaf PEs. The Source AS field of
the C-Multicast routes will be filled with the root distinguishing
value of root PEs which the route is sent to.
5.4. Segmented Inter-AS Scenario
In the regular procedure of [RFC6514], Intra-AS AD route is only used
in non-segmented Inter-AS scenario. In the segmented Inter-AS
scenario, different Intra-AS AD routes originated by different PEs in
the same AS are aggregated to a single Inter-AS AD route on ASBRs
with the granularity of <AS, MVPN>. The specific original root PE's
information is substituted with source AS during the aggregation,
which results in that leaf PEs located in downstream ASes cannot
differentiate two multicast traffic sent by different root PEs in the
same original AS.
In this document, two approaches are proposed to facilitate the root
PE selection of leaf PEs in downstream ASes.
This first approach is to use the wildcard S-PMSI AD route described
in [RFC6625] instead of Intra-AS AD route. As described in
[RFC6514], the S-PMSI AD route will not be aggregated by ASBR while
being used to set up Inter-AS segmented S-PMSI tunnels, result in
that Leaf PE in downstream AS can do explicit tracking of those
tunnels established from the redundant PEs located in upstream AS.
The propagation procedure between ASes follows the description in
section 12.2 of [RFC6514].
The second method is to use PE Distinguisher Labels attribute defined
in [RFC6514] to carry PE address and corresponding upstream assigned
label at the segmentation point. In the segmented scenario, the PE
Distinguisher Labels attribute SHOULD be distributed with the Inter-
AS A-D route. When the multicast traffic is received from the Intra-
AS P-Tunnel from an ingress root PE on ASBR, the ASBR will switch
Intra-AS P-Tunnel to Inter-AS P-Tunnel and add the corresponding PE
Duan, et al. Expires 24 May 2024 [Page 14]
Internet-Draft MVPN Upstream DF Selection November 2023
Distinguisher Label as an inner label into the label stack. In this
way, leaf PE will recognise the root PE of the multicast traffic and
RPF Checking can be performed accordingly. As described in
[RFC6514], leaf PE will find corresponding Inter-AS A-D route while
sending C-multicast route. It fills source-AS field of the
C-multicast route with the corresponding PE Distinguisher Label
carried in the Inter-AS A-D route.
6. Backward Compatibility
When some devices do not support MVPN Upstream IDF Election, the
following procedures are introduced to support the backward
compatibility and end-to-end MVPN service. This section mainly
discuss the situation that root PE and leaf PE does not support the
IDF election function simultaneously.
6.1. Root PE Not Support IDF Election
When a root PE does not support MVPN Upstream IDF Election, the UMH
route sent by the root PE will not carry IDF Negotiation Community.
Other root PEs will check all received UMH routes with the same
prefix. As long as one of these routes does not carry the community,
the IDF election procedures will not be executed and hot root standby
will be conducted.
Leaf PE will also check the received UMH routes. When one of the
received UMH route does not carry the IDF Negotiation Community, the
RPF Set checklist will not be used. The RPF Checking will be based
on the normal procedure that only one upstream interface will be
considered as the valid upstream interface for certain (C-S,C-G).
6.2. Leaf PE Not Support IDF Election
When leaf PE does not support the IDF Election or it cannot become
the leaf of PMSI Tunnel rooted at the main IDF, it must revert back
to join the normal PMSI P-Tunnel to receive multicast traffic. A new
extra PMSI attribute called "Secondary PMSI Tunnel Attribute" is
appended after the existing PTA in the x-PMSI A-D route sent by the
primary and standby IDF to identify the warm PMSI Tunnel. The format
and content of "Secondary PMSI Tunnel Attribute" are same as PTA
defined in [RFC6514]. The attribute type (Attr Type) field will be
allocated by IANA.
When leaf PE does not support the IDF Election function, it cannot
recognise these Secondary attribute. Therefore, the leaf PE will
join the PMSI Tunnel identified by the normal PTA defined in
[RFC6514]. The explicit tracking defined in [RFC6514] will be
conducted. Even if leaf PE supports the IDF Election function, it
Duan, et al. Expires 24 May 2024 [Page 15]
Internet-Draft MVPN Upstream DF Selection November 2023
may not be able to join the "Warm Tunnel" due to certain reasons,
such as local policy. Under this condition, leaf PE can also join
the original PMSI Tunnel.
When leaf PE decide to join the "Warm PMSI Tunnel" identified by the
Secondary PTA, it will send C-Multicast route to root PEs. The
x-PMSI Leaf A-D route will carry a "Secondary Indication Community".
The value of this community will be allocated by IANA.
When root PEs are performing the IDF Election, only IDF can forward
corresponding traffic into the PMSI Tunnel identified by "Secondary
PTA". One multicast traffic can be carried by both the normal PMSI
Tunnel and warm PMSI Tunnel simultaneously. Only the warm PMSI
Tunnel is controlled by the aforementioned IDF Negotiation Status.
7. Security Considerations
This document follows the security considerations specified in
[RFC6513] and [RFC6514]. In addition, because the establishment of
segmented Inter-AS PMSI tunnel is introduced by using Intra-AS AD
routes in this document, the Originator's IP addresses are exposed
between ASes which may cause some security risks in the scenarios of
different service providers for different ASes. In order to reduce
the impact, the Intra-AS AD routes to be leaked between ASes MUST be
controlled under security policies so that the numbers of the leaked
Originator's IP addresses can be reduced.
8. IANA Considerations
This document defines a new BGP Community called IDF negotiation
Community, of which the value will be allocated from IANA for each
negotiation mode individually. The BFD Discriminator Attribute
defined in [RFC9026] is reused and the value of BFD Mode is
recommended to be 2 in this document, which will be reviewed by IANA.
This document defines a new UMH route type for MVPN, of which the
value is recommended to be 8 and will be reviewed by IANA. This
document defines a new BGP Extended Community called "Root
Distinguisher", this Community is of an extended type and is
transitive, the Type and Sub-Type are TBD and will be allocated from
IANA.
This document defines a new PMSI Tunnel Attribute called "Secondary
PMSI Tunnel Attribute" and a new community called "Secondary
Indication Community". Their attribute types will be allocated by
IANA.
Duan, et al. Expires 24 May 2024 [Page 16]
Internet-Draft MVPN Upstream DF Selection November 2023
9. Acknowledgements
The authors wish to thank Jingrong Xie and Jeffrey Zhang, for their
reviews, comments and suggestions.
10. Normative References
[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>.
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010,
<https://www.rfc-editor.org/info/rfc5798>.
[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>.
[RFC6515] Aggarwal, R. and E. Rosen, "IPv4 and IPv6 Infrastructure
Addresses in BGP Updates for Multicast VPN", RFC 6515,
DOI 10.17487/RFC6515, February 2012,
<https://www.rfc-editor.org/info/rfc6515>.
[RFC6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
RFC 6625, DOI 10.17487/RFC6625, May 2012,
<https://www.rfc-editor.org/info/rfc6625>.
[RFC7524] Rekhter, Y., Rosen, E., Aggarwal, R., Morin, T.,
Grosclaude, I., Leymann, N., and S. Saad, "Inter-Area
Point-to-Multipoint (P2MP) Segmented Label Switched Paths
(LSPs)", RFC 7524, DOI 10.17487/RFC7524, May 2015,
<https://www.rfc-editor.org/info/rfc7524>.
Duan, et al. Expires 24 May 2024 [Page 17]
Internet-Draft MVPN Upstream DF Selection November 2023
[RFC7716] Zhang, J., Giuliano, L., Rosen, E., Ed., Subramanian, K.,
and D. Pacella, "Global Table Multicast with BGP Multicast
VPN (BGP-MVPN) Procedures", RFC 7716,
DOI 10.17487/RFC7716, December 2015,
<https://www.rfc-editor.org/info/rfc7716>.
[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>.
[RFC9026] Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
"Multicast VPN Fast Upstream Failover", RFC 9026,
DOI 10.17487/RFC9026, April 2021,
<https://www.rfc-editor.org/info/rfc9026>.
Authors' Addresses
Fanghong Duan
Huawei Technologies
Email: duanfanghong@huawei.com
Siyu Chen
Huawei Technologies
Email: chensiyu27@huawei.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Heng Wang
Ruijie Networks Co., Ltd.
Email: wangheng1@ruijie.com.cn
Duan, et al. Expires 24 May 2024 [Page 18]
