Internet DRAFT - draft-ietf-mboned-redundant-ingress-failover
draft-ietf-mboned-redundant-ingress-failover
MBONED WG G. Shepherd
Internet-Draft Cisco Systems, Inc.
Intended status: Informational Z. Zhang, Ed.
Expires: 26 July 2024 ZTE Corporation
Y. Liu
China Mobile
Y. Cheng
China Unicom
G. Mishra
Verizon Inc.
23 January 2024
Multicast Redundant Ingress Router Failover
draft-ietf-mboned-redundant-ingress-failover-04
Abstract
This document discusses multicast redundant ingress router failover
issues, include global multicast and Service Provider Network MVPN
use case. This document analyzes specification of global multicast
and Multicast VPN Fast Upstream Failover and the Ingress PE Standby
Modes and the benefits of each mode.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF). Note that other groups may also distribute
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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 26 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Multicast Redundant Ingress Router Failover . . . . . . . . . 3
3.1. Swichover . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Failure detection . . . . . . . . . . . . . . . . . . . . 7
4. Stand-by Modes . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Cold Root Standby Mode . . . . . . . . . . . . . . . . . 8
4.2. Warm Root Standby Mode . . . . . . . . . . . . . . . . . 8
4.3. Hot Root Standby Mode . . . . . . . . . . . . . . . . . . 9
4.4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The multicast redundant ingress router failover is an important issue
in multicast deployment. This document tries to do a research on it
in the multicast domain. The Multicast Domain is a domain which is
used to forward multicast flow according to specific multicast
technologies, such as PIM ([RFC7761]), BIER ([RFC8279]), P2MP TE
tunnel ([RFC4875]), MLDP ([RFC6388]), etc. The domain may or may not
connect the multicast source and receiver directly.
The ingress router is close to the multicast source. The ingress
router may connect the multicast source directly, or there may be
multiple hops between the ingress router and the multicast source.
In the multicast domain, the ingress router is the most adjacent
router to the multicast source. It's also called the first-hop
router in PIM, or BFIR in BIER, or Ingress LSR in P2MP TE tunnel or
MLDP.
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The failover function between the multicast source and the ingress
router can be achieved by many ways, and it is not included in this
document.
The egress router is close to the multicast receiver. The egress
router may connect the multicast receiver directly, or there may be
multiple hops between the egress router and the multicast receiver.
In the multicast domain, the egress router is the most adjacent
router to the multicast receiver. It's also called the last-hop
router in PIM, or BFER in BIER, or Egress LSR in P2MP TE tunnel or
MLDP.
There may be some other function deployed in the multicast domain,
such as static configuration, or AMT ([RFC7450]), or SR P2MP Policy
([I-D.ietf-pim-sr-p2mp-policy]).
This document doesn't discuss the details of these technologies.
This document discusses the general redundant ingress router failover
ways in the multicast domain.
This document discusses global multicast and Service Provider Network
MVPN use case with redundant ingress PE nodes Upstream Mulitcast Hop
(UMH) and failover from primary UMH to Standby UMH in a multicast
domain. This document analyzes specification Multicast VPN Fast
Upstream Failover ([RFC9026]) and the Ingress PE Standby Modes and
the benefits of each mode.
2. Terminology
The following abbreviations are used in this document:
IR: the ingress router which is the most close to the multicast
source in the multicast domain.
ER: the egress router which is the most close to the multicast
receiver in the multicast domain.
SIR: The IR that is in charge of sending the multicast flow, or the
flow from the IR is accepted by the ERs, the IR is called as the
Selected-IR, that is SIR in abbreviation.
BIR: The IR that is not in charge of sending the multicast flow, or
the flow from the IR is not accepted by the ERs, but the IR replaces
the role of SIR once SIR fails. The IR is called as the Backup-IR,
that is BIR in abbreviation.
3. Multicast Redundant Ingress Router Failover
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source
...
+-----+ +-----+
+----------+ IR1 +------+ IR2 +---------+
|multicast +-----+ +-----+ |
|domain ... |
| |
| +-----+ +-----+ |
| | Rm | | Rn | |
| ++---++ +--+--+ |
| | | | |
| +-----+ +---+ +-----+ |
| | | | |
| +-v---+ +--v--+ +--v--+ |
+---+ ER1 +------+ ER2 +------+ ER3 +---+
+-----+ +-----+ +-----+
... ... ...
receiver receiver receiver
Figure 1
Usually, a multicast source connects directly, or across multiple
hops to two IRs to avoid single node failure. As shown in figure 1,
there are two IRs close to a multicast source. The two IRs are UMH
(Upstream Multicast Hop) candidates for the ERs.
The two IRs gets multicast flow from the mutlcast source, how to
forward the multicast flow to ERs is different according to the
technologies deployed in the multicast domain. For example, for PIM
which is used in this domain, two PIM Trees that rooted on the two
IRs may be built separately.
The IRs works with the other router, such as the ER, in the multicast
domain to minimize the multicast flow packet loss during the IR
swichover.
3.1. Swichover
There may be some failures occurs in the domain, such as link
failure, node failure, if the failed link or node is on the multicast
flow forwarding path, there may be multicast flow packet loss.
If there are multiple paths from the IR to the ERs, there is no need
to switch IR when some nodes or links fail.
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* When PIM is used in the domain as multicast forwarding protocol,
the forwarding tree for (S, G) or (*, G) is built in advance.
When a node or link in the forwarding tree fails, the tree is
rebuilt partially.
* When BIER is used in the domain as multicast forwarding protocol,
there is no need to rebuilt forwarding tree in case of node or
link failure, the BIER forwarding recovers along with the IGP
routing convergence.
* When P2MP TE tunnel or MLDP is used in the domain as multicast
forwarding protocol, the forwarding LSP is built in advance. When
a node or link in the LSP fails, the LSP may be rebuilt partially.
* When static multicast tree or SR P2MP policy is used in the
domain, the controller needs to re-compute a new forwarding path
to bypass the failed node or link.
In some situations, there are some key nodes or links in the network.
The multicast path can not be recovered due to the key node or link
failure. The IR needs swichover.
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...
+-----+ +-----+
+----------+ IR1 +------+ IR2 +---------+
| +--+--+ +--+--+ |
| | | |
| +--+--+ +--+--+ |
| | Rx | | Ry | |
| +-+-+-+ ++---++ |
| | | | | |
| | +-----------+ | |
| | | | | |
| | +---------+ | | |
| | | | | |
| +-v-v-+ +--v-v+ |
| | Rm | | Rn | |
| ++---++ +--+--+ |
| | | | |
| +-----+ +---+ +-----+ |
| | | | |
| +-v---+ +--v--+ +--v--+ |
+---+ ER1 +------+ ER2 +------+ ER3 +---+
+-----+ +-----+ +-----+
... ... ...
receiver receiver receiver
Figure 2
For example in figure 2, there is only one path in the network
partially. The IR1, Rx are key nodes in the domain, when IR1 or Rx
fails, there is no any other path between the IR1 and the ERs.
* When PIM is used in the domain, Rm and Rn may choose Ry as the
upstream node to send Join message to build a new tree which
rooted with IR2.
* When BIER is used in the domain, IR2 should in charge of the
forwarding role to forward the flow to the ERs.
* When P2MP TE tunnel or MLDP is used in the domain, the LSP started
from IR2 can be built and replace the used LSP started from IR1
when the used LSP does not work.
* When static multicast tree or SR P2MP policy is used in the
domain, the controller should let the IR2 to forward multicast
flow to the ERs.
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3.2. Failure detection
In order to achieve the successful IR switchover, some methods should
be used for monitoring the IR node failure or the path failure
between IR and ERs, and the IR can do the switching once the failure
occurs. BFD or PING methods can be used for it.
BFD [RFC5880] can be used in all the deployments. Multipoint BFD
[RFC8562] can also be used for the failure detection between IR and
ERs. BFD for MPLS LSPs [RFC5884] can be used in P2MP TE tunnel or
MLDP deployments. BIER BFD [I-D.ietf-bier-bfd] can be used in BIER
deployment.
IPv4 PING [RFC0792] and IPv6 PING [RFC4443] can also be used in all
the deployments. LSP-Ping [RFC8029] can be used for P2MP TE tunnel
or MLDP deployments. BIER PING [I-D.ietf-bier-ping] can be used in
BIER deployment.
BIR and ER can detect the SIR node and path failure easily by the BFD
and PING methods. If the monitoring is between SIR and ER, how to
trigger the switchover quickly is challenging when BIR needs to start
forwarding the multicast flow. If the monitoring is between BIR and
SIR, the path between BIR and SIR may fail, but the path is not the
way from SIR to ERs, BIR may trigger the switchover by mistake, in
this case unnecessary duplicate flow occurs. In this case, the ER
must support the selective receiving and can be compatible with the
IR switchover mistake. In order to minimize the mistaken switchover,
the reliability of SIR/BIR detection needs to be enhanced, such as
using redundant reliable paths for detection, etc.
Multicast VPN Fast Upstream Failover [RFC9026] defines a mechanism to
detect the P-Tunnel X-PMSI A-D route status using P2MP BFD [RFC5880]
with a new advertised BGP attribute called a BFP Discriminator
optional transitive attribute
Multicast VPN Fast Upstream Failover [RFC9026] defines a new "Standby
PE" BGP Community that the downstream PE originates and sends a
"Standby BGP C-multicast route" with Standby Upstream PE UMH route RT
import EC that identifies the Standby Upstream PE with NLRI
constructed using RD of Standby Upstream PE UMH route.
4. Stand-by Modes
In case there are more than one IRs can be the UMH, and there is no
other path from an IR to ERs in case of the IR fails, the IR needs to
be switched.
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Usually there are three types of stand-by modes in multicast IR
protection. [RFC9026] has some description on it. This document
discusses the detail of the three modes here.
The ER may send request to upstream router or IR when it finds the
node or path failure. The request from the ER may be the PIM tree
building, or BIER overlay protocol signaling, or LSP building, or
some other ways to let IR knows whether forwards the multicast flow.
4.1. Cold Root Standby Mode
In Cold Root Standby mode, the ER selects an SIR, for example IR1 in
figure 1, as the SIR and signals to it to get the multicast flow.
When the ER finds that the SIR is down, or the ER finds that it
cannot receive flow from IR1, the ER signals to IR2 to get the
multicast flow.
* For IR, the IRs, include SIR and BIR, just do the regular
operation of forwarding flow according to the request from the ER.
* For ER, the ER must select an IR as the SIR and signal to it.
When the SIR fails or the path between the SIR and ER fails, the
ER must signal to the BIR to get the flow.
* For the intermediate routers, they know nothing about the role of
IR, they just do the packet forwarding. There is no duplicate
packets in the domain.
In case of the IR switchover, the ER detects the failure of SIR, and
signals to the BIR. There is packet loss during the signaling until
the ER receives the flow from the BIR.
4.2. Warm Root Standby Mode
In Warm Root Standby Mode, the ER signals to both IR1 and IR2.
In case IR1 is the SIR, IR1 forwards the flow to the ER. The BIR,
for example the IR2, must not forward the flow to the ER until the
SIR is down.
* For IR, the IR should take the role of SIR or BIR. The BIR must
not forward flow to the ER. When the SIR fails or the path
between SIR and ER fails, the BIR must start forwarding the flow
to ER. But it's hard to know the failure for BIR itself, some
methods should be taken to let the BIR to get the failure
notification.
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* For ER, the ER does not select the SIR or BIR. The ER just signal
to both of them.
* For the intermediate routers, they know nothing about the role of
IR, they just do the packet forwarding. There is no duplicate
packets in the domain.
In case of the IR switchover, the BIR detects the failure of the SIR
and switch to SIR. There is packet loss during the IR switchover.
In some deployments, the SIR and BIR may in charge of different
multicast flow. For a specific multicast flow, the SIR may be IR1,
for another multicast flow, the SIR may be IR2. So the two IRs can
share the multicast forwarding load. And another possible deployment
is, the two IRs can in charge of different ERs for one multicast
flow. For example, IR1 sends the multicast flow to some of the ERs,
and IR2 send the multicast flow to the other ERs. In case IR1
detects there is something wrong between IR1 and the ERs, IR1 may
notify IR2 to take over the responsibility of forwarding the
multicast flow to these ERs that receive flow from IR1 before.
4.3. Hot Root Standby Mode
In Hot Root Standby Mode, the ER signals to both IRs.
Both IRs are sending the flow to the ER. The ER must discard the
duplicate flow from one of the IRs.
In this situation, there are no SIR or BIR. Only ER knows which IR
is the SIR.
* For IR, the IR need not to know the roles of SIR or BIR, IR just
forwarding the flow according to the request received from ER.
* For ER, the ER signal to both of the IRs to get the flow. And the
ER must discard the duplicated flow from the backup BIR. When the
SIR fails or the path between SIR and ER fails, the ER must switch
the forwarding plane to forward the flow packet comes from the
BIR. To be noted, the ERs may choose different SIR or BIR.
* For the intermediate routers, they know nothing about the role of
IR, they just do the packet forwarding. There are duplicate
packets forwarded in the domain.
In case of the IR switchover, the ER detects the failure of the SIR.
Because there are duplicate flow packets arrive on the ER, the ER
just switch to forward the flow comes from the BIR. There may be
packet loss during the switching.
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4.4. Summary
The table is a brief comparison among the three modes. The 'SIR
failover' means the SIR fails or the path between SIR and ER fails.
+==============+================+================+=================+
| role | Cold Mode | Warm Mode | Hot Mode |
+==============+================+================+=================+
| IR | Forwarding | Takes the role | Need not to |
| | flow according | of SIR or BIR, | know the roles |
| | to the request | BIR must not | of SIR or BIR, |
| | from ER. | forward flow | just forwarding |
| | | to ER until | flow according |
| | | SIR failovers. | to the request |
| | | | from ER. |
+--------------+----------------+----------------+-----------------+
| ER | Must select an | Does not | Signal to both |
| | IR as SIR to | select the SIR | of SIR and BIR. |
| | signal the | or BIR, just | Discards the |
| | request, | signal to both | duplicate flow |
| | signal to the | of them. | from BIR until |
| | BIR to request | | SIR failover. |
| | the flow when | | |
| | SIR failovers. | | |
+--------------+----------------+----------------+-----------------+
| Intermediate | Knows nothing | Knows nothing | Knows nothing |
| Router | about SIR or | about SIR or | about SIR or |
| | BIR. No | BIR. No | BIR. |
| | duplicated | duplicated | Duplicated flow |
| | flow is | flow is | is forwarded. |
| | forwarded. | forwarded. | |
+--------------+----------------+----------------+-----------------+
Table 1
The Cold root stand-by mode is the easiest way to implementated, but
it takes the longest converge time.
The Hot root stand-by mode takes the most less packet loss, but there
is duplicated packet forwarding in the domain, more bandwidth is
occupied.
The Warm root stand-by mode takes the middle packet loss and converge
time, but it's hard for BIR to know the failure between SIR and ERs.
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The Hot root stand-by mode described in [RFC9026] Section 5 is the
best UMH protection mechanism. There can be duplicated packets
forwarded in the domain which are dropped per [RFC9026] Section 6 and
[RFC6513] Section 9.1. Hot root stand-by mode is the best
recommended method for MVPN Fast Failover optimization.
For the network administrator, the most suitable stand-by mode should
be selected according to the network deployment.
5. IANA Considerations
This document does not have any requests for IANA allocation.
6. Security Considerations
This document adds no new security considerations.
7. References
7.1. Normative References
[RFC4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
DOI 10.17487/RFC4875, May 2007,
<https://www.rfc-editor.org/info/rfc4875>.
[RFC6388] Wijnands, IJ., Ed., Minei, I., Ed., Kompella, K., and B.
Thomas, "Label Distribution Protocol Extensions for Point-
to-Multipoint and Multipoint-to-Multipoint Label Switched
Paths", RFC 6388, DOI 10.17487/RFC6388, November 2011,
<https://www.rfc-editor.org/info/rfc6388>.
[RFC7450] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450,
DOI 10.17487/RFC7450, February 2015,
<https://www.rfc-editor.org/info/rfc7450>.
[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>.
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[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
7.2. Informative References
[I-D.ietf-bier-bfd]
Xiong, Q., Mirsky, G., hu, F., and C. Liu, "BIER BFD",
Work in Progress, Internet-Draft, draft-ietf-bier-bfd-04,
11 September 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-bier-bfd-04>.
[I-D.ietf-bier-ping]
Nainar, N. K., Pignataro, C., Chen, M., and G. Mirsky,
"BIER Ping and Trace", Work in Progress, Internet-Draft,
draft-ietf-bier-ping-12, 29 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
ping-12>.
[I-D.ietf-pim-sr-p2mp-policy]
Voyer, D., Filsfils, C., Parekh, R., Bidgoli, H., and Z.
J. Zhang, "Segment Routing Point-to-Multipoint Policy",
Work in Progress, Internet-Draft, draft-ietf-pim-sr-p2mp-
policy-07, 11 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pim-sr-
p2mp-policy-07>.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
June 2010, <https://www.rfc-editor.org/info/rfc5884>.
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[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>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[RFC8562] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) for
Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
April 2019, <https://www.rfc-editor.org/info/rfc8562>.
[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
Greg Shepherd
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose,
United States of America
Email: gjshep@gmail.com
Zheng Zhang (editor)
ZTE Corporation
Nanjing
China
Email: zhang.zheng@zte.com.cn
Yisong Liu
China Mobile
Beijing
Email: liuyisong@chinamobile.com
Ying Cheng
China Unicom
Beijing
China
Email: chengying10@chinaunicom.cn
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Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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