BESS Working Group Dave Allan, Jeff Tantsura
Internet Draft Ericsson
Intended status: Standards Track Don Fedyk
Expires: April 2016 HP
Ali Sajassi
Cisco
September 2015
Shortest Path Bridging, MAC Mode Support over EVPN
draft-ietf-bess-spbm-evpn-01
Abstract
This document describes how Ethernet Shortest Path Bridging MAC mode
(802.1aq) can be combined with EVPN to interwork with PBB-PEs as
described in the PBB-EVPN solution. This is achieved via
operational isolation of each Ethernet network subtending an EVPN
core while supporting full interworking between the different
variations of Ethernet networks.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance
with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet
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This Internet-Draft will expire on February 2016.
Copyright and License Notice
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Copyright (c) 2015 IETF Trust and the persons identified as the
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction...................................................2
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 802.1aq SPBM island or PBB-PE to
EVPN..............................................................8
4.6. Data plane Interworking EVPN to 802.1aq SPBM island..........8
4.7. Data plane interworking EVPN to 802.1ah PBB-PE...............8
4.8. Multicast Support............................................8
5. Other Aspects..................................................9
5.1. Transit......................................................9
6. Acknowledgements...............................................9
7. Security Considerations........................................9
8. IANA Considerations...........................................10
9. References....................................................10
9.1. Normative References........................................10
9.2. Informative References......................................10
10. Authors' Addresses...........................................11
1. Introduction
This document describes how Ethernet Shortest Path Bridging MAC mode
(SPBM) 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
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isolated while providing full L2 connectivity between the different
types of PBBNs where desired. Each SPBM island uses its own control
plane instance and multi-pathing 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 RFC2119 [RFC2119].
2. Conventions used in this document
2.1. Terminology
BEB: Backbone Edge Bridge
BGP: Border Gateway Protocol
B-MAC: Backbone MAC Address
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: I-Component Service ID
NLRI: Network Layer Reachability Information
PBB: Provider Backbone Bridging (802.1ah)
PBBN: Provider Backbone Bridged Network
PBB-PE: Co located 802.1ah BEB and EVPN PE
PE: Provider Edge
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SPB: Shortest Path Bridging
SPBM: Shortest Path Bridging MAC mode
SPBM-PE: Co-located 802.1aq SPBM<->EVPN interworking function and
EVPN PE
3. Solution Overview
The EVPN solution for 802.1aq SPBM incorporates control plane
interworking in the PE to map ISIS-SPB [RFC6329] information elements
into the EVPN Next Layer Reachabilty 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 subtending SPBM islands may be
interconnected without any topological or multipathing dependencies.
This model also permits PBB-PEs as defined in [PBB-EVPN] 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 multi-homed onto an IP/MPLS network that
implements EVPN for the purpose of interconnect 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
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(how multi-pathing 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 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
in [PBB-EVPN] which allows multiple gateways per B-VID (each with
different I-SIDs) across the EVPN is supported by the interworking
between PBBNs and SPBM networks. However SPBM only allows a single
active designated forwarder 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
associated Ethernet Segment ID (ESI) 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 subtending 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 designated forwarder (DF) for the B-VID. An SPBM-PE may 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 the following procedures:
4.1. PE Configuration
At SPBM island commissioning a PE is configured with:
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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 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.
2) The set of B-VIDs used in the SPBM island and multi-pathing
algorithm IDs to use for each. The set of B-VIDs and multi-
pathing algorithms used may 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 of 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 of
[RFC7432] "Designated Forwarder election".
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 it 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 are processed accordingly.
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- 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). The encoding of I-SID information is as per figure 2.
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 sub-TLV
- a locally assigned MPLS label
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 information associated with the new role of the
PE.
If the BGP database has NLRI information for the I-SID, and this is
the first instance of registration of interest in the I-SID from the
SPBM island, the NLRI information with that tag 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 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 of this memo.
4.4. Control plane interworking EVPN to ISIS-SPB
When a PE receives a BGP NLRI that has new information, it 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 it is an elected DF for. 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 not of interest. If the I-SID
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is of local interest to the SPBM island and the PE is the DF for the
B-VID that the I-SID is locally mapped to, a SPBM service identifier
and unicast address sub-TLV is constructed/updated for advertisement
into ISIS-SPB.
The NLRI information 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 being that obtained from the NLRI.
4.5. Data plane Interworking 802.1aq SPBM island or PBB-PE to EVPN
When an 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 802.1aq SPBM island
When a PE receives a packet from the EVPN it may 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 802.1ah PBB-PE
A PBB-PE actually has no subtending 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 802.1ah encoded multicast DAs. The only information of interest
being 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.
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5. Other Aspects
5.1. Transit
Any PE that does not need to participate in the tandem calculations
at the B-MAC layer may use the IS-IS overload bit to exclude SPBM
tandem paths and behave as pure interworking platform.
6. Acknowledgements
The authors would like to thank Peter Ashwood-Smith, Martin Julien
and Janos Farkas for their detailed review of this draft.
7. Security Considerations
Security issues associated with incorrect interconnect 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 (EVPN will assume that separate networks are
interconnected by SPBM). Security issues exist when SPBM domains are
incorrectly cross connected together via EVPN which will result in
back-holing or incorrect delivery of data with associated privacy
issues. This could be achieved by provisioning the incorrect RT value
at an SPBM-PE or associating the RT with the wrong interface. This
can be avoided via care in route target provisioning at SPBM-PEs for
service adds and changes.
The potentially most destructive behavior of the overall system would
be frequent changes to the DF elections for a given ESI. This would
require SPBM-PEs to frequently flap in the form of either the node
continuously resetting or links flapping in a form that keeps
severing and re-connecting the SPBM-PE from either the IP/MPLS
network or the subtending 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.
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The issues associated with securing the BGP control plane
(independent of this particular memo) are reflected in the security
considerations section of [RFC4761].
8. IANA Considerations
No IANA assignments are required by this document.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4761] Kompella (ed.), "Virtual Private LAN Service (VPLS) Using BGP
for Auto-Discovery and Signaling", IETF RFC 4761, January 2007
[RFC6329] Fedyk et.al. "IS-IS Extensions Supporting IEEE 802.1aq
Shortest Path Bridging", IETF RFC 6329, April 2012
[RFC7432] Aggarwal et.al. "BGP MPLS Based Ethernet VPN", IETF RFC
7432, February 2015
9.2. Informative References
[802.1aq]
802.1aq(2012) IEEE Standard for Local and Metropolitan
Area Networks: Bridges and Virtual Bridged Local Area
Networks - Amendment 9: Shortest Path Bridging
[PBB-EVPN] Sajassi et.al. "PBB E-VPN", IETF work in progress,
draft-ietf-l2vpn-pbb-evpn-10, May 2015
[802.1Q]
802.1Q (2011) IEEE Standard for Local and metropolitan
area networks--Media Access Control (MAC) Bridges and
Virtual Bridged Local Area Networks
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10. Authors' Addresses
Dave Allan (editor)
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: david.i.allan@ericsson.com
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
Email: jeff.tantsura@ericsson.com
Don Fedyk
Hewlett-Packard
153 Tayor Street
Littleton, MA, 01460
don.fedyk@hp.com
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
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