Internet Engineering Task Force (IETF) D. Allan, Ed.

Internet Engineering Task Force (IETF) D. Allan, Ed.
Request for Comments: 7734 J. Tantsura
Category: Standards Track Ericsson
ISSN: 2070-1721 D. Fedyk
HPE
A. Sajassi
Cisco
January 2016

Support for Shortest Path Bridging MAC Mode over Ethernet VPN (EVPN)

Abstract

This document describes how Ethernet Shortest Path Bridging MAC mode
(SPBM) can be combined with Ethernet VPN (EVPN) to interwork with
Provider Backbone Bridging Provider Edges (PBB PEs) as described in
the PBB-EVPN solution (RFC 7623). This is achieved via operational
isolation of each Ethernet network attached to an EVPN core while
supporting full interworking between the different variations of
Ethernet networks.

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 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7734.

Allan, et al. Standards Track [Page 1]

RFC 7734 SPBM Support over EVPN January 2016

Copyright Notice

Copyright (c) 2016 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
(http://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 ....................................................3
1.1. Requirements Language ......................................3
2. Conventions Used in This Document ...............................3
2.1. Terminology ................................................3
3. Solution Overview ...............................................4
4. Elements of Procedure ...........................................5
4.1. PE Configuration ...........................................5
4.2. DF Election ................................................6
4.3. Control-Plane Interworking ISIS-SPB to EVPN ................6
4.4. Control-Plane Interworking EVPN to ISIS-SPB ................7
4.5. Data-Plane Interworking SPBM Island or PBB PE to EVPN ......8
4.6. Data-Plane Interworking EVPN to SPBM Island ................8
4.7. Data-Plane Interworking EVPN to PBB PE .....................8
4.8. Multicast Support ..........................................8
5. Other Aspects ...................................................8
5.1. Transit ....................................................8
6. Security Considerations .........................................9
7. References .....................................................10
7.1. Normative References ......................................10
7.2. Informative References ....................................10
Acknowledgments ...................................................11
Authors' Addresses ................................................11

Allan, et al. Standards Track [Page 2]

RFC 7734 SPBM Support over EVPN January 2016

1. Introduction

This document describes how Ethernet Shortest Path Bridging MAC mode
(SPBM) [IEEE.802.1Q] along with Provider Backbone Bridging Provider
Edges (PBB PEs) and Provider Backbone Bridged Networks (PBBNs) can be
supported by Ethernet VPNs (EVPNs) such that each SPBM island is
operationally isolated while providing full L2 connectivity between
the different types of PBBNs where desired. Each SPBM island uses
its own control-plane instance and multipathing design, be it
multiple equal-cost tree sets or multiple spanning trees.

The intention is to permit past, current, and emerging future
versions of Ethernet to be seamlessly interconnected to permit large-
scale, geographically diverse numbers of Ethernet end systems to be
fully supported with EVPN as the unifying system.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. Conventions Used in This Document

2.1. Terminology

Terms used in this document are used as specified in IEEE
802.1Q-2014, which incorporates earlier IEEE 802.1 projects.

BEB: Backbone Edge Bridge
BGP: Border Gateway Protocol
B-MAC: Backbone MAC
B-VID: Backbone VLAN ID
CE: Customer Edge
DA: Destination Address
DF: Designated Forwarder
ESI: Ethernet Segment Identifier
EVPN: Ethernet VPN
IB-BEB: A BEB that has both an I-component (customer-layer VLAN-aware
bridge) and a B-component (backbone-layer VLAN-aware bridge)
ISIS-SPB: IS-IS as extended for SPB
I-SID: Backbone Service Instance Identifier
NLRI: Network Layer Reachability Information
PBB: Provider Backbone Bridging as in Clauses 25 and 26 of
[IEEE.802.1Q]
PBBN: Provider Backbone Bridged Network
PBB PE: Co-located BEB and EVPN PE
PE: Provider Edge

Allan, et al. Standards Track [Page 3]

RFC 7734 SPBM Support over EVPN January 2016

SPB: Shortest Path Bridging
SPBM: Shortest Path Bridging MAC mode as in Clauses 27 and 28 of
[IEEE.802.1Q]
SPBM-PE: Co-located SPBM<->EVPN interworking function and EVPN PE

3. Solution Overview

The EVPN solution for SPBM, as specified in [IEEE.802.1Q],
incorporates control-plane interworking in the PE to map ISIS-SPB
[RFC6329] information elements into the EVPN Next Layer Reachability
Information (NLRI) and vice versa. This requires each PE to act both
as an EVPN BGP speaker and as an ISIS-SPB edge node. Associated with
this are procedures for configuring the forwarding operations of the
PE such that an arbitrary number of EVPN-attached SPBM islands can be
interconnected without any topological or multipathing dependencies.
This model also permits PBB PEs as defined in [RFC7623] to seamlessly
communicate with the SPBM islands.

+--------------+ +----+ +---+
| | |PBB |---|CE2|
| | |PE3 | +---+
+-----+ +----+ | | +----+
| |-----|SPBM| | |
|SPBM | |PE1 | | IP/MPLS |
+---+ |NTWK1| +----+ | Network |
|CE1|-| | | |
+---+ | | +----+ | |
| |-----|SPBM| | | +----+ +-----+
+-----+ |PE2 | | | |SPBM| |SPBM | +---+
+----+ | | |PE5 |---|NTWK2|-|CE3|
+--------------+ +----+ +-----+ +---+

Figure 1: PBB and SPBM EVPN Network

Figure 1 illustrates the generalized space addressed by this memo.
SPBM networks may be multihomed onto an IP/MPLS network that
implements EVPN for the purpose of interconnecting with other SPBM
networks and/or PBB PEs. The multipathing configuration of each SPBM
network can be unique as the backbone VLAN ID (B-VID) configuration
(how multipathing is performed in SPBM) is not propagated across the
IP/MPLS network implementing EVPN. As with PBB networking, the B-VID
is local to the SPBM network, so in SPBM a B-MAC associated with the
B-VID is advertised with the supported I-SIDs at the PBB gateway.

Each EVPN is identified by a route target. I-SID-based load-
balancing as specified in [RFC7623] allows multiple gateways per
B-VID (each with different I-SIDs) across the EVPN; it is supported
by the interworking between PBBNs and SPBM networks. However, SPBM

Allan, et al. Standards Track [Page 4]

RFC 7734 SPBM Support over EVPN January 2016

only allows a single active designated forwarder (DF) per B-VID as
described below. The route target identifies the set of SPBM islands
and PBB PEs that are allowed to communicate. Each SPBM island is
administered to have an Ethernet Segment ID (ESI) Label extended
community associated with it.

BGP acts as a common repository of the I-Component Service ID (I-SID)
attachment points for the set of attached PEs / SPBM islands. This
is in the form of {B-MAC address, I-SID, Tx-Rx-attribute} tuples.
BGP distributes I-SID information into each SPBM island on the basis
of locally registered interest. If an SPBM island has no Backbone
Edge Bridges (BEBs) registering interest in a particular I-SID,
information about that I-SID from other SPBM islands, PBB PEs, or
PBBNs MUST NOT be leaked into the local ISIS-SPB routing system. For
each B-VID in an SPBM island, a single SPBM-PE MUST be elected the DF
for the B-VID. An SPBM-PE can be a DF for more than one B-VID. This
is described further in Section 4.2. The SPBM-PE originates IS-IS
advertisements as if it were an IB-BEB that proxies for the other
SPBM islands and PBB PEs in the EVPN defined by the route target, but
the PE typically will not actually host any I-components.

An SPBM-PE that is a DF for a B-VID MUST strip the B-VID tag
information from frames relayed towards the EVPN. The DF MUST also
insert the appropriate B-VID tag information into frames relayed
towards the SPBM island on the basis of the local I-SID/B-VID
bindings advertised in ISIS-SPB.

4. Elements of Procedure

A PE MUST implement and perform the following procedures.

4.1. PE Configuration

At SPBM island commissioning a PE is configured with:

1) The route target for the service instance. Where a route target
is defined as identifying the set of SPBM islands, PBBNs and
PBB PEs are to be interconnected by the EVPN.

2) The unique ESI for the SPBM island. Mechanisms for deriving a
unique ESI for the SPBM island are out of scope.

The following is configured as part of commissioning an ISIS-SPB
node:

1) A Shortest Path Source ID (SPSourceID) used for algorithmic
construction of multicast addresses. Note this is required for
SPBM BEB operation independent of the EVPN operation.

Allan, et al. Standards Track [Page 5]

RFC 7734 SPBM Support over EVPN January 2016

2) The set of B-VIDs used in the SPBM island and multipathing
algorithm IDs to use for each. The set of B-VIDs and multipathing
algorithms used can be different in different domains. Therefore,
the B-VID is local to an SPBM domain and is removed for frames
carried over the IP/MPLS network.

A Type 1 Route Distinguisher for the node can be auto-derived. The
actual procedure is out of scope for this document.

4.2. DF Election

PEs self-appoint themselves for the role of DF for a B-VID for a
given SPBM island. The procedure used is as per Section 8.5
(Designated Forwarder Election) of [RFC7432].

A PE that assumes the role of DF for a given B-VID is responsible for
originating specific information into BGP from ISIS-SPB and vice
versa. A PE that ceases to perform the role of DF for a given B-VID
is responsible for withdrawing the associated information from BGP
and ISIS-SPB, respectively. The actual information exchanged is
outlined in the following sections.

4.3. Control-Plane Interworking ISIS-SPB to EVPN

When a PE receives an SPBM service identifier and unicast address
sub-TLV as part of an ISIS-SPB MT capability TLV, the PE checks if it
is the DF for the B-VID in the sub-TLV.

If it is the DF, and there is new or changed information, then a
MAC/IP advertisement route NLRI is created for each new I-SID in the
sub-TLV. Changed information that results in modification to
existing NLRI is processed accordingly. NLRI creation/modification
will ensure:

- the Route Distinguisher is set to that of the PE.

- the ESI is that of the SPBM island.

- the Ethernet Tag ID contains the I-SID (including the Tx/Rx
attributes) copied from the SPBM service identifier and unicast
address sub-TLV. The encoding of I-SID information is as per
Figure 2. (See [RFC6329] for details on the T bit and R bit.)

Allan, et al. Standards Track [Page 6]

RFC 7734 SPBM Support over EVPN January 2016

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|R| Reserved | I-SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: I-SID Encoding in the Ethernet Tag ID Field

- the MAC address is copied from the SPBM service identifier and
unicast address sub-TLV

- a locally assigned MPLS label (which may be common with other NLRI
originated by the PE and is used to map EVPN traffic to the SPBM
network)

Similarly, in the scenario where a PE became elected DF for a B-VID
in an operating network, the IS-IS database would be processed in
order to construct the NLRI associated with the new role of the PE.

If the BGP database has NLRI for the I-SID, and this is the first
instance of registration of interest in the I-SID from the SPBM
island, the NLRI for the I-SID is processed to construct an updated
set of SPBM service identifier and unicast address sub-TLVs to be
advertised by the PE.

The ISIS-SPB information is also used to keep current a local table
indexed by I-SID to indicate the associated B-VID for processing of
frames received from the EVPN. When an I-SID is associated with more
than one B-VID, only one entry is allowed in the table. Rules for
preventing this are out of scope for this memo.

4.4. Control-Plane Interworking EVPN to ISIS-SPB

When a PE receives a BGP NLRI that has new information, the PE checks
if it is the elected DF to communicate this information into ISIS-SPB
by checking if the I-SID in the Ethernet Tag ID locally maps to the
B-VID for which it is an elected DF. Note that if no BEBs in the SPB
island have advertised any interest in the I-SID, it will not be
associated with any B-VID locally, and therefore will not be of
interest. If the I-SID is of local interest to the SPBM island and
the PE is the DF for the B-VID to which the I-SID is locally mapped,
a SPBM service identifier and unicast address sub-TLV are
constructed/updated for advertisement into ISIS-SPB.

The NLRI advertised into ISIS-SPB is also used to locally populate a
forwarding table indexed by B-MAC + I-SID that points to the label
stack to impose on the SPBM frame. The bottom label in the stack is
that obtained from the NLRI.

Allan, et al. Standards Track [Page 7]

RFC 7734 SPBM Support over EVPN January 2016

4.5. Data-Plane Interworking SPBM Island or PBB PE to EVPN

When a PE receives a frame from the SPBM island in a B-VID for which
it is a DF, it looks up the B-MAC/I-SID information to determine the
label stack to be added to the frame for forwarding in the EVPN. The
PE strips the B-VID information from the frame, adds the label
information to the frame, and forwards the resulting MPLS packet.

4.6. Data-Plane Interworking EVPN to SPBM Island

When a PE receives a packet from the EVPN, it can infer the B-VID to
overwrite in the SPBM frame from the I-SID or by other means (such as
via the bottom label in the MPLS stack).

If the frame has a local multicast destination address (DA), it
overwrites the SPSourceID in the frame with the local SPSourceID.

4.7. Data-Plane Interworking EVPN to PBB PE

A PBB PE actually has no attached PBBN nor concept of B-VID, so no
frame processing is required.

A PBB PE is required to accept SPBM-encoded multicast DAs as if they
were PBB-encoded (i.e., using the Backbone Service Instance Group
address) for multicast DAs. The only information of interest is that
it is a multicast frame and the I-SID encoded in the lower 24 bits.

4.8. Multicast Support

Within a PBBN domain, Ethernet unicast and multicast end services are
supported. PBB can tunnel multicast traffic in unicast PBB frames
when using head-end replication. This is the only form of multicast
traffic interworking supported by this document. Native PBB
multicast forwarding over EVPN, PE replication, or optimizing PBB
multicast across the EVPN is not addressed by this memo.

5. Other Aspects

5.1. Transit

Any PE that does not need to participate in the tandem calculations
at the B-MAC layer can use the IS-IS overload bit to exclude SPBM
tandem paths and behave as a pure interworking platform.

Allan, et al. Standards Track [Page 8]

RFC 7734 SPBM Support over EVPN January 2016

6. Security Considerations

Security issues associated with incorrect interconnection of customer
LANs cannot be directly addressed by implementations of this
document, as it requires misconfiguration in the Shortest Path
Bridging domains. The identifiers so administered have global
significance to the larger system. They are relayed transparently by
EVPN and only policed in the SPBM domains. Therefore, care is
required in synchronization of identifiers that need to be common for
inter-domain operation.

There are only two identifiers unique to this solution provisioned at
an SPBM-PE at service turn-up: the route target and the ESI. The ESI
needs to be unique and common to all SPBM-PEs connected to a common
SPBM network or PBBN, else portions of the overall network will not
share reachability. (The EVPN will assume that separate networks are
interconnected by SPBM.) Security issues exist when SPBM domains are
incorrectly cross-connected together via EVPN; this will result in
black-holing or incorrect delivery of data with associated privacy
issues. This error may occur by provisioning the incorrect RT value
at an SPBM-PE or associating the RT with the wrong interface. This
error can be avoided by consistency-checking the route target
provisioning at SPBM-PEs when performing service additions and/or
changes.

The behavior that is potentially most destructive to the overall
system is frequent changes to the DF elections for a given ESI. This
would occur if the SPBM-PEs continuously had their links go up and
down in a such a way that the SPBM-PE was being severed from and
reconnected to either the IP/MPLS network or the attached SPBM
network. Either of these scenarios would result in significant
control-plane traffic as DF associated information was advertised and
withdrawn from both the SPBM and BGP control planes. Dual-homing of
SPBM-PEs on both networks would minimize the likelihood of this
scenario occurring.

The issues associated with securing the BGP control plane
(independent of this particular memo) are reflected in the Security
Considerations section of [RFC4761].

Allan, et al. Standards Track [Page 9]

RFC 7734 SPBM Support over EVPN January 2016

7. References

7.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC4761] Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
<http://www.rfc-editor.org/info/rfc4761>.

[RFC6329] Fedyk, D., Ed., Ashwood-Smith, P., Ed., Allan, D., Bragg,
A., and P. Unbehagen, "IS-IS Extensions Supporting IEEE
802.1aq Shortest Path Bridging", RFC 6329,
DOI 10.17487/RFC6329, April 2012,
<http://www.rfc-editor.org/info/rfc6329>.

[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, <http://www.rfc-editor.org/info/rfc7432>.

7.2. Informative References

[IEEE.802.1Q]
IEEE, "IEEE Standard for Local and metropolitan area
networks--Bridges and Bridged Networks", IEEE 802.1Q-2014,
DOI 10.1109/ieeestd.2014.6991462, December 2014.

[RFC7623] Sajassi, A., Ed., Salam, S., Bitar, N., Isaac, A., and W.
Henderickx, "Provider Backbone Bridging Combined with
Ethernet VPN (PBB-EVPN)", RFC 7623, DOI 10.17487/RFC7623,
September 2015, <http://www.rfc-editor.org/info/rfc7623>.

Allan, et al. Standards Track [Page 10]

RFC 7734 SPBM Support over EVPN January 2016

Acknowledgments

The authors would like to thank Peter Ashwood-Smith, Martin Julien,
and Janos Farkas for their detailed reviews of this document.

Authors' Addresses

Dave Allan (editor)
Ericsson
300 Holger Way
San Jose, CA 95134
United States

Email: [email protected]

Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
United States

Email: [email protected]

Don Fedyk
Hewlett-Packard Enterprise
153 Taylor Street
Littleton, MA 01460
United States

Email: [email protected]

Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134
United States

Email: [email protected]

Allan, et al. Standards Track [Page 11]