P2MP BFD for TRILL: Support of Point-to-Multipoint Bidirectional Forwarding Detection (BFD) in Transparent Interconnection of Lots of Links (TRILL)
How a TRILL bridge can check, with one multicast probe stream, that its multicast paths to many other bridges still work.
Zhang, M., Pallagatti, S., and V. Govindan, "Support of Point-to-Multipoint Bidirectional Forwarding Detection (BFD) in Transparent Interconnection of Lots of Links (TRILL)", RFC 8564, DOI 10.17487/RFC8564, April 2019, <https://www.rfc-editor.org/info/rfc8564>.
@misc{rfc8564,
series = {Request for Comments},
number = 8564,
howpublished = {RFC 8564},
publisher = {RFC Editor},
doi = {10.17487/RFC8564},
url = {https://www.rfc-editor.org/info/rfc8564},
author = {M. Zhang and S. Pallagatti and V. Govindan},
title = {{Support of Point-to-Multipoint Bidirectional Forwarding Detection (BFD) in Transparent Interconnection of Lots of Links (TRILL)}},
pagetotal = 8,
year = 2019,
month = apr,
} RFC text
Contents
Internet Engineering Task Force (IETF) M. Zhang
Request for Comments: 8564 Huawei Technologies
Updates: 7175, 7177 S. Pallagatti
Category: Standards Track Vmware
ISSN: 2070-1721 V. Govindan
Cisco Systems
April 2019
Support of Point-to-Multipoint Bidirectional Forwarding Detection (BFD)
in Transparent Interconnection of Lots of Links (TRILL)
Abstract
Point-to-multipoint (P2MP) Bidirectional Forwarding Detection (BFD)
is designed to verify multipoint connectivity. This document
specifies the support of P2MP BFD in Transparent Interconnection of
Lots of Links (TRILL). Similar to TRILL point-to-point BFD, BFD
Control packets in TRILL P2MP BFD are transmitted using RBridge
Channel messages. This document updates RFCs 7175 and 7177.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8564.
Copyright Notice
Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Acronyms and Terminology . . . . . . . . . . . . . . . . . . 3
2.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Bootstrapping . . . . . . . . . . . . . . . . . . . . . . . . 3
4. A New RBridge Channel Message for P2MP BFD . . . . . . . . . 4
5. Discriminators and Packet Demultiplexing . . . . . . . . . . 4
6. Tracking Active Tails . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
TRILL supports multicast forwarding. Applications based on TRILL
multicast may need quick detection of multicast failures using P2MP
BFD [RFC8562]. This document specifies TRILL support of P2MP BFD.
To use P2MP BFD, the head end needs to periodically transmit BFD
Control packets to all tails using TRILL multicast. A new RBridge
Channel message is allocated for this purpose.
In order to execute the global protection of distribution used for
multicast forwarding [TRILL-TREES], the head needs to track the
active status of tails [RFC8563]. If the tail loses connectivity as
detected by not receiving the new RBridge Channel message from the
head, the tail should notify the head of the lack of multipoint
connectivity with unicast BFD Control packets. These unicast BFD
Control packets are transmitted using the existing RBridge Channel
message assigned to BFD Control [RFC7175].
This document updates [RFC7177] as specified in Section 3 and updates
[RFC7175] as specified in Sections 4 and 5.
2. Acronyms and Terminology
2.1. Acronyms
Data Label: VLAN or Fine-Grained Label [RFC7172].
BFD: Bidirectional Forwarding Detection
P2MP: Point to Multipoint
TRILL: Transparent Interconnection of Lots of Links or Tunneled
Routing in the Link Layer
2.2. 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.
Familiarity with [RFC6325], [RFC7175], and [RFC7178] is assumed in
this document.
3. Bootstrapping
The TRILL adjacency mechanism bootstraps the establishment of one-
hop TRILL BFD sessions [RFC7177]. Multi-hop sessions are expected to
be configured by the network manager. A slight wording update to the
second sentence in Section 6 of [RFC7177] is required.
It currently reads:
If an RBridge supports BFD [RFC7175], it will have learned whether
the other RBridge has BFD enabled by whether or not a BFD-Enabled
TLV [RFC6213] was included in its Hellos.
Now it should read:
If an RBridge supports BFD (see [RFC7175] and [RFC8564]), it will
have learned whether the other RBridge has BFD enabled by whether
or not a BFD-Enabled TLV [RFC6213] was included in its Hellos.
In addition, a normative reference to this document is added to RFC
7177 as a result of this update.
4. A New RBridge Channel Message for P2MP BFD
RBridge Channel protocol number 0x002 is defined for TRILL point-to-
point BFD Control packets in [RFC7175]. That RFC states that if the
M bit of the TRILL Header of the RBridge Channel packet containing a
BFD Control packet is nonzero, the packet is generally dropped. In
P2MP BFD, the head is required to probe tails using multicast. This
means the M bit will be set to 1. For this reason, a new RBridge
Channel message (P2MP BFD Control), whose protocol code point is
0x007, is specified in this document. An RBridge that supports P2MP
BFD MUST support the new RBridge Channel message for P2MP BFD. The
capability to support the RBridge Channel message for P2MP BFD, and
therefore support performing P2MP BFD, is announced within the
RBridge Channel Protocols sub-TLV in Link State PDUs (LSPs)
[RFC7176].
As specified in [RFC7178], when the tail receives TRILL Data packets
sent as BFD RBridge Channel messages, it will absorb the packets
itself rather than deliver these packets to its attached end
stations.
5. Discriminators and Packet Demultiplexing
The processing in Section 3.2 of [RFC7175] generally applies except
that the test on the M bit in the TRILL Header is reversed. If the M
bit is zero, the packet MUST be discarded. If the M bit is one, it
is processed.
After the processing per Section 3.2 of [RFC7175], the tail
demultiplexes incoming BFD packets based on a combination of the
source address and My Discriminator as specified in [RFC8562]. In
addition to this combination, TRILL P2MP BFD requires that the tail
use the Data Label, which is either the inner VLAN or the Fine-
Grained Label [RFC7172], for demultiplexing. If the tail needs to
notify the head about the failure of a multipath, the tail is
required to send unicast BFD Control packets using the same Data
Label as used by the head.
6. Tracking Active Tails
According to [RFC8562], the head has a session of type MultipointHead
that is bound to a multipoint path. Multipoint BFD Control packets
are sent by this session over the multipoint path, and no BFD Control
packets are received by it. Each tail dynamically creates a
MultipointTail per a multipoint path. MultipointTail sessions
receive BFD Control packets from the head over multipoint paths.
An example use is when a multicast tree root needs to keep track of
all the receivers as in [TRILL-TREES]; this can be done by
maintaining a session of type MultipointClient per receiver that is
of interest, as described in [RFC8563]. See [RFC8563] for detailed
operations of tracking active tails.
7. Security Considerations
Multipoint BFD provides its own authentication but does not provide
encryption (see the Security Considerations in [RFC8562]). As
specified in this document, the point-to-multipoint BFD payloads are
encapsulated in RBridge Channel messages that have been extended by
[RFC7978] to provide security. [RFC7978] provides encryption only
for point-to-point extended RBridge Channel messages, so its
encryption facilities are not applicable to this document. However,
[RFC7978] provides stronger authentication than that currently
provided in BFD. Thus, there is little reason to use the BFD
security mechanisms if authentication per [RFC7978] is in use. It is
expected that a future TRILL document will provide for group keying;
when that occurs, the use of RBridge Channel security [RFC7978] will
be able to provide both encryption and authentication.
For general multipoint BFD security considerations, see [RFC8562].
For general RBridge Channel security considerations, see [RFC7178].
8. IANA Considerations
IANA has allocated the following from the Standards Action [RFC8126]
range of the "RBridge Channel Protocols" registry, which is part of
the "Transparent Interconnection of Lots of Links (TRILL) Parameters"
registry.
Protocol Number
---------------- ------
P2MP BFD Control 0x007
9. References
9.1. 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>.
[RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
<https://www.rfc-editor.org/info/rfc6325>.
[RFC7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172,
DOI 10.17487/RFC7172, May 2014,
<https://www.rfc-editor.org/info/rfc7172>.
[RFC7175] Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
"Transparent Interconnection of Lots of Links (TRILL):
Bidirectional Forwarding Detection (BFD) Support",
RFC 7175, DOI 10.17487/RFC7175, May 2014,
<https://www.rfc-editor.org/info/rfc7175>.
[RFC7176] Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
D., and A. Banerjee, "Transparent Interconnection of Lots
of Links (TRILL) Use of IS-IS", RFC 7176,
DOI 10.17487/RFC7176, May 2014,
<https://www.rfc-editor.org/info/rfc7176>.
[RFC7177] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
V. Manral, "Transparent Interconnection of Lots of Links
(TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177, May
2014, <https://www.rfc-editor.org/info/rfc7177>.
[RFC7178] Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
Ward, "Transparent Interconnection of Lots of Links
(TRILL): RBridge Channel Support", RFC 7178,
DOI 10.17487/RFC7178, May 2014,
<https://www.rfc-editor.org/info/rfc7178>.
[RFC7978] Eastlake 3rd, D., Umair, M., and Y. Li, "Transparent
Interconnection of Lots of Links (TRILL): RBridge Channel
Header Extension", RFC 7978, DOI 10.17487/RFC7978,
September 2016, <https://www.rfc-editor.org/info/rfc7978>.
[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>.
[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>.
[RFC8563] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
<https://www.rfc-editor.org/info/rfc8563>.
9.2. Informative References
[RFC6213] Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV",
RFC 6213, DOI 10.17487/RFC6213, April 2011,
<https://www.rfc-editor.org/info/rfc6213>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[TRILL-TREES]
Zhang, M., Senevirathne, T., Pathangi, J., Banerjee, A.,
and A. Ghanwani, "TRILL: Resilient Distribution Trees",
Work in Progress, draft-ietf-trill-resilient-trees-09,
January 2018.
Acknowledgements
The authors would like to thank Gayle Noble and Donald Eastlake 3rd
for their comments and suggestions.
Authors' Addresses
Mingui Zhang
Huawei Technologies
No.156 Beiqing Rd. Haidian District
Beijing 100095
China
Email: zhangmingui@huawei.com
Santosh Pallagatti
Vmware
Email: santosh.pallagatti@gmail.com
Vengada Prasad Govindan
Cisco Systems
Email: venggovi@cisco.com
AI ELI5
On this page
§1Why TRILL Needs P2MP BFD
TRILL supports multicast forwarding. Applications built on TRILL multicast may need to detect multicast failures quickly, and the tool for that is point-to-multipoint (P2MP) BFD from RFC 8562. This RFC specifies how TRILL supports it.
The head end periodically sends BFD Control packets to all tails using TRILL multicast. A new RBridge Channel message is allocated for this purpose. To run the global protection of distribution used for multicast forwarding, the head also needs to track the active status of tails, as described in RFC 8563.
If a tail stops receiving the new message from the head, it should tell the head about the lack of multipoint connectivity. It does so with unicast BFD Control packets, sent using the existing RBridge Channel message for BFD Control from RFC 7175.
One bridge keeps shouting 'I am still here' to many others. Anyone who stops hearing it quietly tells the shouter.
§3Bootstrapping Sessions
The TRILL adjacency mechanism bootstraps one-hop TRILL BFD sessions, as described in RFC 7177. Multi-hop sessions are expected to be configured by the network manager.
One small wording change to RFC 7177 is needed. The second sentence of its Section 6 used to say that an RBridge supporting BFD learns whether a neighbor has BFD enabled from the BFD-Enabled TLV in its Hellos. It now says that an RBridge supporting BFD (see RFC 7175 and RFC 8564) learns this in the same way. A normative reference to this document is added to RFC 7177 as a result.
Neighbors who are next door find each other automatically. Farther-away partners have to be set up by hand by the person running the network.
§4The New RBridge Channel Message
RFC 7175 defines RBridge Channel protocol number 0x002 for point-to-point BFD Control packets. It says such a packet is generally dropped if the M bit in the TRILL Header is nonzero. A P2MP head probes tails by multicast, so the M bit will be 1.
For that reason this document defines a new RBridge Channel message, P2MP BFD Control, with protocol code point 0x007. An RBridge that supports P2MP BFD MUST support this message. The capability is announced in the RBridge Channel Protocols sub-TLV in Link State PDUs (LSPs), per RFC 7176.
As specified in RFC 7178, a tail that receives these TRILL Data packets absorbs them itself rather than delivering them to attached end stations.
The old message was for talking to one friend and was thrown away if sent to a crowd. So a new kind of message was made just for talking to a crowd.
| Aspect | Point-to-point BFD (RFC 7175) | P2MP BFD (RFC 8564) |
|---|---|---|
| RBridge Channel protocol | 0x002 | 0x007 |
| M bit in TRILL Header THIS RFC | Nonzero: packet generally dropped | Zero: packet MUST be discarded; one: processed |
§5Discriminators and Demultiplexing
Processing follows Section 3.2 of RFC 7175, except that the M bit test is reversed. If the M bit is zero, the packet MUST be discarded. If it is one, the packet is processed.
The tail then demultiplexes incoming BFD packets using the source address and My Discriminator, as in RFC 8562. TRILL adds a requirement: the tail must also use the Data Label (the inner VLAN or the Fine-Grained Label from RFC 7172).
If the tail has to tell the head that a multipath has failed, it MUST send unicast BFD Control packets using the same Data Label the head used.
A tail sorts incoming messages by who sent them, which number they carry and which group they belong to. It answers using the same group name it heard.
- P2MP BFD Control (multicast)Sent periodically over the multicast path.
- BFD Control (unicast)Sent if the tail loses multipoint connectivity, using the same Data Label.
§6Tracking Active Tails
Under RFC 8562, the head has a session of type MultipointHead bound to a multipoint path. It sends multipoint BFD Control packets over that path and receives none. Each tail dynamically creates a MultipointTail session for each multipoint path, and these sessions receive the head's packets.
A multicast tree root that needs to keep track of all receivers can maintain a MultipointClient session per receiver of interest, as described in RFC 8563. This RFC leaves the detailed operation of tracking active tails to that document.
The head keeps a roll call of the listeners it cares about, and each listener keeps a note of which shouting head it is hearing.
§7Security Considerations
Multipoint BFD has its own authentication but no encryption. Here, the P2MP BFD payloads travel in RBridge Channel messages that RFC 7978 extended to provide security. RFC 7978 gives encryption only for point-to-point extended messages, so its encryption does not apply here. Its authentication is stronger than what BFD offers, so there is little reason to use BFD's own mechanisms when RFC 7978 authentication is in use.
The RFC expects a future TRILL document to provide group keying. At that point RBridge Channel security would offer both encryption and authentication.
The messages can be signed so that nobody can fake them, but for now they cannot be locked in a box when sent to a whole crowd.
§8IANA Considerations
IANA allocated one value from the Standards Action range of the 'RBridge Channel Protocols' registry, part of the TRILL Parameters registry: P2MP BFD Control, number 0x007.
The official list of message types got one new entry, number 7, for the crowd-talking message.