Internet DRAFT - draft-ietf-l2vpn-pbb-vpls-interop
draft-ietf-l2vpn-pbb-vpls-interop
INTERNET-DRAFT Ali Sajassi
L2VPN Working Group Samer Salam
Intended Status: Informational Cisco
Nabil Bitar
Verizon
Florin Balus
Nuage Networks
Expires: April 21, 2014 October 21, 2013
VPLS Interoperability with Provider Backbone Bridges
draft-ietf-l2vpn-pbb-vpls-interop-06
Abstract
The scalability of Hierarchical Virtual Private LAN Service (H-VPLS)
with Ethernet access networks [RFC4762] can be improved by
incorporating Provider Backbone Bridge functionality in the VPLS
access. Provider Backbone Bridging has been standardized as IEEE
802.1ah-2008, and aims to improve the scalability of MAC addresses
and service instances in Provider Ethernet networks. This document
describes different interoperability scenarios where Provider
Backbone Bridge functionality is used in H-VPLS with Ethernet or MPLS
access network to attain better scalability in terms of number of
customer MAC addresses and number of service instances. The document
also describes the scenarios and the mechanisms for incorporating
Provider Backbone Bridge functionality within H-VPLS with existing
Ethernet access and interoperability among them. Furthermore, the
document discusses the migration mechanisms and scenarios by which
Provider Backbone Bridge functionality can be incorporated into H-
VPLS with existing MPLS access.
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 Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
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Copyright (c) 2013 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. H-VPLS with Homogeneous PBBN Access . . . . . . . . . . . . . . 7
4.1 Service Interfaces and Interworking Options . . . . . . . . 9
4.2 H-VPLS with PBBN Access: Type I Service Interface . . . . . 10
4.3 H-VPLS with PBBN Access: Type II Service Interface . . . . . 12
5. H-VPLS with Mixed PBBN Access and PBN Access . . . . . . . . . 14
5.1 H-VPLS with Mixed PBBN & PBN Access: Modified PBN PE . . . . 15
5.2 H-VPLS with Mixed PBBN & PBN Access: Regular PBN PE . . . . 16
6. H-VPLS with MPLS Access . . . . . . . . . . . . . . . . . . . . 18
6.1 H-VPLS with MPLS Access: PBB U-PE . . . . . . . . . . . . . 18
6.2 H-VPLS with MPLS Access: PBB N-PE . . . . . . . . . . . . . 20
7. H-VPLS with MPLS Access: PBB Migration Scenarios . . . . . . . 21
7.1 802.1ad Service Frames over VPLS Core . . . . . . . . . . . 21
7.2 PBB Service Frames over VPLS Core . . . . . . . . . . . . . 22
7.3 Mixed 802.1ad and PBB over VPLS Core . . . . . . . . . . . . 23
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8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 24
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
10. Security Considerations . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1 Normative References . . . . . . . . . . . . . . . . . . . 25
11.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
The scalability of Hierarchical Virtual Private LAN Service (H-VPLS)
with Ethernet access networks [RFC4762] can be improved by
incorporating Provider Backbone Bridge functionality in the VPLS
access. Provider Backbone Bridging has been standardized as IEEE
802.1ah-2008 [802.1ah], which is an amendment to IEEE 802.1Q to
improve the scalability of Media Access Control (MAC) addresses and
service instances in Provider Ethernet networks. This document
describes interoperability scenarios where IEEE 802.1ah functionality
is used in H-VPLS with Ethernet or MPLS access network to attain
better scalability in terms of the number of customer MAC addresses
and the number of services.
This document also covers the interoperability scenarios for
deploying H-VPLS with Provider Backbone Bridging Ethernet access when
other types of access networks are deployed, including existing
802.1ad Ethernet and MPLS access in either single or multiple service
domains. Furthermore, the document explores the scenarios by which an
operator can gradually migrate an existing H-VPLS network to Provider
Backbone Bridging over VPLS.
Section 2 gives a quick terminology reference and section 3
highlights the applicability of Provider Backbone Bridging
interoperation with VPLS. Section 4 describes H-VPLS with
homogeneous Provider Backbone Bridge Access Network. Section 5
discusses H-VPLS with mixed 802.1ah/802.1ad access. Section 6 focuses
on Provider Backbone Bridging in H-VPLS with MPLS Access Network
including Provider Backbone Bridge function on U-PE and on N-PE
variants. Finally, section 7 describes gradual migration scenarios
from existing H-VPLS to Provider Backbone Bridging over H-VPLS.
2. Terminology
802.1ad: IEEE specification for "QinQ" encapsulation and bridging of
Ethernet frames
802.1ah: IEEE specification for "MAC tunneling" encapsulation and
bridging of frames across a provider backbone bridged network.
B-BEB: A backbone edge bridge positioned at the edge of a provider
backbone bridged network. It contains a B-component that supports
bridging in the provider backbone based on B-MAC and B-TAG
information
B-MAC: The backbone source or destination MAC address fields defined
in the 802.1ah provider MAC encapsulation header.
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BCB: A backbone core bridge running in the core of a provider
backbone bridged network. It bridges frames based on B-TAG
information just as an 802.1ad provider bridge will bridge frames
based on a VLAN identifier (S-VLAN)
B-Component: The backbone component of a Provider Backbone edge
bridge as defined in [802.1ah].
BEB: A backbone edge bridge positioned at the edge of a provider
backbone bridged network. It can contain an I-component, B-component
or both I and B components.
B-MACs: Backbone MAC addresses - outer MAC addresses of a PBB
encapsulated frame
B-TAG: field defined in the 802.1ah provider MAC encapsulation
header that conveys the backbone VLAN identifier information. The
format of the B-TAG field is the same as that of an 802.1ad S-TAG
field.
B-Tagged Service Interface: This is the interface between a BEB and
BCB in a provider backbone bridged network. Frames passed through
this interface contain a B-TAG field.
B-VID: The specific VLAN identifier carried inside a B-TAG
C-MACs: Customer MAC addresses - inner MAC addresses of a PBB
encapsulated frame
H-VPLS: Hierarchical Virtual Private LAN Service
I-component: A bridging component contained in a backbone edge bridge
that bridges in the customer space (customer MAC addresses, S-VLAN)
IB-BEB: A backbone edge bridge positioned at the edge of a provider
backbone bridged network. It contains an I-component for bridging in
the customer space (customer MAC addresses, service VLAN IDs) and a
B-component for bridging the provider's backbone space (B-MAC, B-
TAG).
I-BEB: A backbone edge bridge positioned at the edge of a provider
backbone bridged network. It contains an I-component for bridging in
the customer space (customer MAC addresses, service VLAN IDs).
I-SID: The 24-bit service instance field carried inside the I-TAG. I-
SID defines the service instance that the frame should be "mapped
to".
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I-TAG: A field defined in the 802.1ah provider MAC encapsulation
header that conveys the service instance information (I-SID)
associated with the frame.
I-Tagged Service Interface: This the interface defined between the I
and B components inside an IB-BEB or between two B-BEB. Frames passed
through this interface contain an I-TAG field
N-PE: Network-facing Provider Edge
PBB: Provider Backbone Bridge
PBBN: Provider Backbone Bridged Network
PBN: Provider Bridged Network. A network that employs 802.1ad (QinQ)
technology.
S-TAG: A field defined in the 802.1ad QinQ encapsulation header that
conveys the service VLAN identifier information (S-VLAN).
S-Tagged Service Interface: This the interface defined between the
customer (CE) and the I-BEB or IB-BEB components. Frames passed
through this interface contain an S-TAG field.
S-VLAN: The specific service VLAN identifier carried inside an S-TAG
U-PE: User-facing Provider Edge
VPLS: Virtual Private LAN Service
3. Applicability
[RFC4762] describes a two-tier hierarchical solution for VPLS for the
purpose of improved pseudowire (PW) scalability. This improvement is
achieved by reducing the number of PE devices connected in a full-
mesh topology through connecting CE devices via the lower-tier access
network, which in turn is connected to the top-tier core network.
[RFC4762] describes two types of H-VPLS network topologies - one with
an MPLS access network and another with an IEEE 802.1ad (QinQ)
Ethernet access network. In both types of H-VPLS, MAC address
learning and forwarding are based on customer MAC addresses (C-MACs),
which poses scalability issues as the number of VPLS instances (and
thus customer MAC addresses) increases. Furthermore, since a set of
PWs is maintained on a per customer service instance basis, the
number of PWs required at N-PE devices is proportional to the number
of customer service instances multiplied by the number of N-PE
devices in the full-mesh set. This can result in scalability issues
(in terms of PW manageability and troubleshooting) as the number of
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customer service instances grows.
In addition to the above, H-VPLS with 802.1ad Ethernet access network
has another scalability issue in terms of the maximum number of
service instances that can be supported in the access network as
described in [RFC4762]. Since the number of provider VLANs (S-VLANs)
is limited to 4K and each S-VLAN represents a service instance in an
802.1ad network, then the maximum number of service instances that
can be supported is 4K. These issues are highlighted in [RFC6246].
This document describes how IEEE 802.1ah (aka Provider Backbone
Bridges) can be integrated with H-VPLS to address these scalability
issues. In the case of H-VPLS with 802.1ah Ethernet access, the
solution results in better scalability in terms of both number of
service instances and number of C-MACs in the Ethernet access network
and the VPLS core network, as well as number of PWs in VPLS core
network. And in the case of H-VPLS with MPLS access, Provider
Backbone Bridging functionality can be used at the U-PE or N-PE which
results in reduction of customer MAC addresses and number of PWs in
the VPLS core network.
The interoperability scenarios depicted in this document fall into
the following two categories:
- Scenarios where Provider Backbone Bridging seamlessly works with
current VPLS implementations (e.g. section 4.2).
- Scenarios where VPLS PE implementations need to be upgraded in
order to work with Provider Backbone Bridging (e.g. sections 4.3,
5.1).
4. H-VPLS with Homogeneous PBBN Access
PBBN access offers MAC-address table scalability for H-VPLS PE nodes.
This is due to the MAC tunneling encapsulation scheme of PBB which
only exposes the provider's own MAC addresses to PE nodes (B- MACs of
Provider's PBB-capable devices in the access network), as opposed to
customers' MAC addresses in conventional H-VPLS with MPLS or 802.1ad
access.
PBBN access also offers service instance scalability when compared to
H-VPLS with 802.1Q/802.1ad access networks. This is due to the new
24-bit service identifier (I-SID) used in PBB encapsulation, which
allows up to 16M services per PBB access network, compared to 4K
services per 802.1Q/802.1ad access network.
Another important advantage of PBBN access is that it offers clear
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separation between the service layer (represented by I-SID) and the
network layer (represented by B-VLAN). B-VLANs segregate a PBB access
network into different broadcast domains and possibly unique
spanning-tree topologies, with each domain being able to carry
multiple services (i.e. I-SIDs). In 802.1ad access networks, the
network and service layers are the same (represented by S-VLAN).
This separation allows the provider to manage and optimize the PBB
access network topology independent of the number of service
instances that are supported.
In this and the following sections we look into different flavors of
H-VPLS with PBBN access. This section discusses the case where H-
VPLS is deployed with homogenous PBBNs access. Section 5 describes
the case where at least one of the access networks is PBN access
(QinQ/802.1ad) while others are PBBNs.
At a macro scale, a network that employs H-VPLS with PBBN access can
be represented as shown in figure 1 below.
+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | |VPLS| |VPLS| | |--| CE |
+----+ | PBBN |---| PE | | PE |--| PBBN | +----+
+----+ | 802.1ah | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 1: H-VPLS with PBBN Access
In the context of PBBN and H-VPLS interoperability, "I-SID Domain"
and "B-VLAN Domain" can be defined as follows:
- "I-SID Domain" refers to a network administrative boundary under
which all the PBB BEBs and VPLS PE devices use the same I-SID space,
i.e. the I-SID assignment is carried out by the same administration.
This effectively means that a given service instance has the same I-
SID designation on all devices within an I-SID Domain.
- "B-VLAN Domain" refers to a network administrative boundary under
which all the PBB BEBs and VPLS PE devices employ consistent I-SID to
B-VLAN bundling - e.g., grouping of I-SIDs to B-VLANs are the same in
that domain. Although the two B-VLANs in two PBBNs that represent the
same group of I-SIDs do not need to use the same B-VID value, in
practice they often use the same value because once the I-SID
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grouping is made identical in two PBBNs, it is very easy to make the
values of the corresponding B-VIDs also identical.
Consequently, three different kinds of "Service Domains" are defined
in the following manner:
- Tightly Coupled Service Domain - Different PBBNs access belonging
to the same I-SID Domain and B-VLAN Domain. However, the network
control protocols (e.g. xSTP) run independently in each PBBN access.
- Loosely Coupled Service Domain - Different PBBNs access belonging
to the same I-SID Domain. However, each PBBN access maintains its own
independent B-VLAN Domain. Again, the network control protocols (e.g.
xSTP) run independently in each PBBN access.
- Different Service Domain - In this case, each PBBN access maintains
its own independent I-SID Domain and B-VLAN Domain, with independent
network control protocols (e.g. xSTP) in each PBBN access.
In general, correct service connectivity spanning networks in a
Tightly Coupled Service Domain can be achieved via B-VID mapping
between the networks (often even without B-VID translation). However,
correct service connectivity spanning networks in a Loosely Coupled
Service Domain requires I-SID to B-VID re-mapping (i.e unbundling and
re-bundling of I-SIDs into B-VIDs). Furthermore, service connectivity
spanning networks in Different Service Domains requires both I-SID
translation and I-SID to B-VID re-mapping.
4.1 Service Interfaces and Interworking Options
Customer devices will interface with PBBN edge bridges using existing
Ethernet interfaces including IEEE 802.1Q and IEEE 802.1ad. At the
PBBN edge, customer MAC frames are encapsulated in a PBB header that
includes a service provider source and destination MAC addresses (B-
MACs) and are bridged up to the VPLS PE. The PBB encapsulated
customer MAC frame is then injected into the VPLS backbone network,
delivered to the remote VPLS PE node(s), and switched onto the remote
PBBN access. From there, the PBBN bridges the encapsulated frame to a
PBBN edge bridge where the PBB header is removed and the customer
frame is sent to the customer domain.
Interoperating between PBBN devices and VPLS PE nodes can leverage
the BEB functions already defined in [802.1ah]. When I-SID visibility
is required at the VPLS PE nodes, a new service interface based on I-
SID tag will need to be defined.
Moreover, by mapping a bridge domain (e.g. B-VLAN) to a VPLS
instance, and bundling multiple end-customer service instances,
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represented by I-SIDs, over the same bridge domain, service providers
will be able to significantly reduce the number of full-mesh PWs
required in the core. In this case, I-SID visibility is not required
on the VPLS-PE and the I-SID will serve as the means of
multiplexing/de-multiplexing individual service instances in the PBBN
over a bundle (e.g. B-VLAN).
When I-SID visibility is expected across the service interface at the
VPLS PE, the VPLS PE can be considered to offer service-level
interworking between PBBN access and IP/MPLS core. Similarly, when
the PE is not expected to have visibility of I-SID at the service
interface, the VPLS PE can be considered to offer network-level
interworking between PBBN access and MPLS core.
A VPLS PE is always part of the IP/MPLS core, and may optionally
participate in the control protocols (e.g. xSTP) of the access
network. When connecting to a PBBN access, the VPLS PE needs to
support one of the following two types of service interfaces:
- Type I: B-Tagged Service Interface with B-VID as Service Delimiter
The PE connects to a Backbone Core Bridge (BCB) in the PBBN access.
The handoff between the BCB and the PE is B-Tagged PBB encapsulated
frames. The PE is transparent to PBB encapsulations and treats these
frames as 802.1ad frames since the B-VID EtherType is the same as the
S-VID EtherType. The PE does not need to support PBB functionality.
This corresponds to conventional VPLS PE's tagged service interface.
When using Type I service interface, the PE needs to support either
raw-mode or tagged-mode Ethernet PW. Type I Service Interface is
described in detail in Section 4.2.
- Type II: I-Tagged Service Interface with I-SID as Service
Delimiter
The PE connects to a B-BEB (Backbone Edge Bridge with B-Component) in
the PBBN access. The PE itself also supports the B-BEB functionality
of [802.1ah]. The handoff between the B-BEB in the PBBN access and
the PE is an I-Tagged PBB encapsulated frame. With Type II service
interface, the PE supports the existing raw-mode and tagged-mode PW
types. Type II Service Interface is described in detail in Section
4.3.
4.2 H-VPLS with PBBN Access: Type I Service Interface
This is a B-Tagged service interface with B-VID as service delimiter
on the VPLS-PE. It does not require any new functionality on the
VPLS-PE. As shown in Figure 2, the PE is always part of the IP/MPLS
core. The PE may also be part of the PBBN Access (e.g. VPLS-PE on
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right side of Figure 2) by participating in network control protocols
(e.g. xSTP) of the PBBN access.
PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------------+
| | +----+ | | |
| +---+ |VPLS| +-+ | | +---+ |
| |BCB|---| PE |---|P| | | |BCB| |
| +---+ /+----+ /+-+ | | /+---+ |
|+---+ | / +----+ / +----+ / +---+|
+--+ ||IB-| +---+/ |VPLS|/ +-+ |VPLS|/ +---+ |IB-|| +--+
|CE|-||BEB|-|BCB|---| PE |---|P|--| PE |---|BCB|-|BEB|--|CE|
+--+ |+---+ +---+ ^ +----+ +-+ +----+ ^ +---+ +---+| +--+
| | | | | | | |
+---------+ | | | +--|------------+
| +--------------+ |
| |
Type I Type I
Figure 2: H-VPLS with PBBN Access & Type I Service Interface
Type I service interface is applicable to networks with Tightly
Coupled Service Domains, where both I-SID Domains and B-VLAN Domains
are the same across all PBBN access networks.
The BCB and the VPLS PE will exchange PBB encapsulated frames that
include source and destination B-MACs, a B-VID and I-SID. The service
delimiter, from the perspective of the VPLS PE, is the B-VID; in
fact, this interface operates exactly as a current 802.1Q/ad
interface into a VPLS PE does today. With Type I service interface,
the VPLS PE can be considered as providing network-level interworking
between PBBN and MPLS domains, since VPLS PE does not have visibility
of I-SIDs.
The main advantage of this service interface, when compared to other
types, is that it allows the service provider to save on the number
of full-mesh PWs required in the core. This is primarily because
multiple service instances (I-SIDs) are bundled over a single full-
mesh corresponding to a bridge domain (e.g. B-VID), instead of
requiring a dedicated full-mesh per service instance. Another
advantage is the MAC address scalability in the core since the core
is not exposed to C-MACs.
The disadvantage of this interface is the comparably excessive
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replication required in the core: since a group of service instances
share the same full-mesh of PWs, an unknown unicast, multicast or
broadcast on a single service instance will result in a flood over
the core. This, however, can be mitigated via the use of per I-SID
flood containment (B-MAC multicast pruning).
Three different modes of operation are supported by Type I Service
Interface:
- Port Mode: All traffic over an interface in this mode is mapped to
a single VPLS instance. Existing PW signaling and Ethernet raw mode
(0x0005) PW type, defined in [RFC4447] [RFC4448], are supported.
- VLAN Mode: all traffic associated with a particular VLAN identified
by the B-VID is mapped to a single VPLS instance. Existing PW
signaling and Ethernet raw mode (0x0005) PW type, defined in
[RFC4447] [RFC4448], are supported.
- VLAN Bundling Mode: all traffic associated with a group or range of
VLANs or B-VIDs is mapped to a single VPLS instance. Existing PW
signaling and Ethernet raw mode (0x0005) PW type, defined in
[RFC4447] [RFC4448], are supported.
For the VLAN mode, it is also possible to use Ethernet tagged mode
(0x0004) PW, as defined in [RFC4447] [RFC4448], for interoperability
with equipment that does not support raw mode. The use of raw mode is
recommended to be the default though.
4.3 H-VPLS with PBBN Access: Type II Service Interface
This is an I-Tagged service interface with I-SID as service delimiter
on the VPLS-PE. It requires the VPLS-PE to include B-Component of PBB
BEB for I-SID processing in addition to the capability to map I-SID
Bundle to VPLS instance. As shown in Figure 3, the PE is always part
of the IP/MPLS core and connects to one or more B-BEB in the PBBN
access.
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PBBN Access IP/MPLS Core PBBN Access
+--------------+
+---------+ | | +---------+
| | | | | |
| +---+ +-----+ | | +---+ |
| |B- | |PE w/| +-+ | | |BCB| |
| |BEB|--|B-BEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
|+---+ +---+/ +-----+/ +-----+ +---+ +---+|
+--+ ||IB-| |B- | |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||BEB|-|BEB|--|B-BEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | | | | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
Type II Type II
Figure 3: H-VPLS with PBBN Access & Type II Service Interface
Type II service interface is applicable to Loosely Coupled Service
Domains and Different Service Domains. B-VLAN Domains can be
independent and the B-VID is always locally significant in each PBBN
access and does not need to be transported over the IP/MPLS core.
Given the above, it should be apparent that Type II service interface
is applicable to Tightly Coupled Service Domains as well.
By definition the B-BEB connecting to the VPLS PE will remove any B-
VLAN tags for frames exiting the PBBN access. The B-BEB and VPLS PE
will exchange PBB encapsulated frames that include source and
destination B-MACs, and I-SID. The service delimiter, from the
perspective of the VPLS PE, is the I-SID. Since the PE has visibility
of I-SIDs, the PE provides service-level interworking between PBBN
access and IP/MPLS core.
Type II Service Interface may operate in I-SID Bundling Mode: all
traffic associated with a group or range of I-SIDs is mapped to a
single VPLS instance. The PE maintains a mapping of I-SIDs to a PE
local bridge domain (e.g. B-VID). The VPLS instance is then
associated with this bridge domain. With Loosely Coupled Service
Domains, no I-SID translation needs to be performed. Type II Service
Interface also supports Different Service Domains in this mode, since
the B-BEB link in the PE connecting to the local PBBN can perform the
translation of PBBN-specific I-SID to a local I-SID within the
IP/MPLS core, which may then be translated to the other PBBN specific
I-SID on the egress PE. Such translation can also occur in the B-BEB
of PBBN access. Existing PW signaling and Ethernet raw mode (0x0005),
defined in [RFC4447] [RFC4448], is supported. It is also possible to
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use tagged mode (0x0004) PW for purpose of interoperability with
equipment that does not support raw mode.
Type II service interface provides operators with the flexibility to
trade-off PW state vs. multicast flooding containment, since a full-
mesh of PWs can be set up:
a. per I-SID,
b. per group of I-SIDs or
c. for all I-SIDs.
For (a) and (b), the advantage that the Type II service interface has
compared to Type I is that it can reduce replication in the core
without the need for a per I-SID flood containment (B-MAC multicast
pruning) mechanism. This is mainly due to the increased segregation
of service instances over disjoint full-meshes of PWs. For (c), both
Type II and Type I service interfaces are at par with regards to
flood containment.
For (a) and (b), the disadvantage of this service interface, compared
to Type I, is that it may require a larger number of full-mesh PWs in
the core. For (c), both Type II and Type I service interfaces are at
par with regards to PW state. However, for all three scenarios, the
number of full-mesh PWs can still be less than those required by H-
VPLS without PBBN access, since an I-SID can multiplex many S-VLANs.
It is expected that this interface type will be used for customers
with significant multicast traffic (but without multicast pruning
capability in the VPLS PE) so that a separate VPLS instance is set up
per group of customers with similar geographic locality (per I-SID
group).
Note: Port mode is not called out in Type II Service Interface since
it requires the mapping of I-SIDs to be identical on different I-
Tagged interfaces across VPLS network. If this is indeed the case,
Port mode defined in Type I Service Interface (Section 4.2) can be
used.
5. H-VPLS with Mixed PBBN Access and PBN Access
It is foreseeable that service providers will want to interoperate
their existing PBN (QinQ) access networks with PBBN access networks
over H-VPLS. Figure 4 below shows the high-level network topology.
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+--------------+
| |
+---------+ | IP/MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| PBN | |VPLS| |VPLS| | |--| CE |
+----+ | (QinQ) |---| PE1| | PE2|--| PBBN | +----+
+----+ | 802.1ad | +----+ +----+ | 802.1ah | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 4: H-VPLS with Mixed PBN and PBBN Access Networks
Referring to Figure 4 above, two possibilities come into play
depending on whether the interworking is carried out at PE1 or PE2.
These are described in the following sub-Sections.
5.1 H-VPLS with Mixed PBBN & PBN Access: Modified PBN PE
As shown in Figure 5, the operation of VPLS PE2 (connecting to the
PBBN access on the right) is no different from what was discussed in
Section 4. Type II service interface, as discussed in the above
section, is applicable. It is the behavior of VPLS PE1 (connecting to
the PBN access on the left) that is the focus of this section.
PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ |PE w/| +-+ | | |BCB| |
| |PCB|--|IBBEB|-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ |PE w/| +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--|IBBEB|-|P|-|B-BEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
Figure 5: H-VPLS with Mixed PBN and PBBN Access: Modified PBN PE
Some assumptions made for this topology include:
- CE is directly connected to PBBN via S-Tagged or port-based
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interface
- I-SID in PBBN access represents the same customer as S-VID in PBN
access
- At S-Tagged Service Interface of PE with IB-BEB functionality (e.g.
PE1 in Figure 5), the only viable service is 1:1 mapping of S-VID to
I-SID. However, towards the core network side, the same PE can
support I-SID bundling into a VPLS instance.
- PE1 participates in the local I-SID domain of the IP/MPLS Core so
the model accommodates for the rest of the PBB network any of the
three domain types described in section 4 - Tightly, Loosely Coupled
and Different Service Domains.
- For ease of provisioning in these disparate access networks, it is
recommended to use the same I-SID Domain among the PBBN access
networks and the PEs with IB-BEB functionality (those connecting to
PBN).
This topology operates in I-SID Bundling Mode: at a PE connecting to
PBN access, each S-VID is mapped to an I-SID and subsequently a group
of I-SIDs is mapped to a VPLS instance. Similarly, at a PE connecting
to PBBN access, each group of I-SIDs is mapped to a VPLS instance.
Similar to Type II interface, no I-SID translation is performed for
I-SID bundling case. Existing PW signaling and Ethernet raw mode
(0x0005) PW type, defined in [RFC4447] [RFC4448], are supported. It
is possible to use tagged mode (0x0004) PW for backward compatibility
as well.
5.2 H-VPLS with Mixed PBBN & PBN Access: Regular PBN PE
As shown in Figure 6, the operation of VPLS PE1 (connecting to the
PBN access on the left) is no different from existing VPLS PEs. It is
the behavior of VPLS PE2 (connecting to the PBBN access on the right)
that is the focus of this section.
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PBN Access IP/MPLS Core PBBN Access
(802.1ad) +--------------+ (802.1ah)
| | +---------+
+---------+ | | | |
| | +-----+ | | +---+ |
| +---+ | PE | +-+ | | |BCB| |
| |PCB|--| |-|P| | | +---+ |
| +---+ /+-----+ +-+ | | / | |
| | / +-----+/ +-----+ +---+ +---+|
+--+ |+---+ +---+ | PE | +-+ |PE w/| |B- | |IB-|| +--+
|CE|-||PEB|-|PCB|--| |-|P|-|IBBEB|-|BEB| |BEB|--|CE|
+--+ |+---+ +---+ ^+-----+ +-+ +-----+^+---+ +---+| +--+
| | | |PE1 PE2| | | |
+---------+ | | | | +---------+
| +-------------+ |
| |
S-Tagged Type II (I-Tagged)
Figure 6: H-VPLS with Mixed PBN and PBBN Access: Regular PBN PE
Some assumptions made for this topology include:
- CE is directly connected to the PBBN access via S-Tagged or port-
based Interface
- I-SID in the PBBN access represents the same customer as S-VID in
the PBN access
- There is 1:1 mapping between the I-SID and the VPLS instance
- At S-Tagged Service Interface of PE connecting to PBN (e.g. PE1 in
Figure 6), the PE only provides 1:1 mapping of S-VID to VPLS
instance. S-VID bundling is not a viable option since it does not
correspond to anything in the PBBN access.
- The PE connecting to the PBBN access (e.g. PE2 in Figure 6),
supports IB-BEB functionality and the I-Component is connected to the
VPLS Forwarder (i.e. the I-Component faces the IP/MPLS core whereas
the B-Component faces the PBBN access network). One or more I-SIDs
can be grouped into a B-VID in the PBBN access.
- Since C-VID grouping in different PBBN access networks must be
consistent, it is assumed that same I-SID Domain is used across
these PBBN access networks.
Unlike the previous case, I-SID bundling mode is not supported in
this case. This is primarily because the VPLS core operates in the
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same manner as today. The PE with IB-BEB functionality connecting to
PBBN access performs the mapping of each VPLS instance to an I-SID
and one or more of these I-SIDs may be mapped onto a B-VID within the
PBBN access network.
6. H-VPLS with MPLS Access
In this section, the case of H-VPLS with MPLS access network is
discussed. The integration of PBB functionality into VPLS-PE for such
access networks is described to improve the scalability of the
network in terms of the number of MAC addresses and service instances
that are supported.
For this topology, it is possible to embed PBB functionality in
either the U-PE or the N-PE. Both of these cases are described in the
following sub-sections.
6.1 H-VPLS with MPLS Access: PBB U-PE
As stated earlier, the objective for incorporating PBB function at
the U-PE is to improve the scalability of H-VPLS networks in terms of
the number of MAC addresses and service instances that are
supported.
In current H-VPLS, the N-PE must learn customer MAC addresses (C-
MACs) of all VPLS instances that it participates in. This can easily
add-up to hundreds of thousands or even millions of C-MACs at the N-
PE. When the U-PE performs PBB encapsulation, the N-PE only needs to
learn the MAC addresses of the U-PEs, which is a significant
reduction. Furthermore, when PBB encapsulation is used, many I-SIDs
are multiplexed within a single bridge domain (e.g., B-VLAN). If the
VPLS instance is set up per B-VLAN, then one can also achieve a
significant reduction in the number of full-mesh PWs. It should be
noted that this reduction in full-mesh PWs comes at the cost of
potentially increased replication over the full-mesh of PWs: Customer
multicast and/or broadcast frames are effectively broadcasted within
the B-VLAN. This may result in additional frame replication because
the full-mesh PWs corresponding to a B-VLAN is most likely bigger
than the full-mesh PWs corresponding to a single I-SID. However, per
I-SID flood containment (B-MAC multicast pruning) can be used to
remedy this drawback and have multicast traffic replicated
efficiently for each customer (i.e. for each I-SID).
Figure 7 below illustrates the scenario for H-VPLS with MPLS access.
As it can be seen, customer networks or hosts (CE) connect into the
U-PE nodes using standard Ethernet interfaces [802.1D], [802.1Q], or
[802.1ad]. The U-PE is connected upstream to one or more VPLS N-PE
nodes by MPLS PWs (per VPLS instance). These, in turn, are connected
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via a full-mesh of PWs (per VPLS instance) traversing the IP/MPLS
core. The U-PE is outfitted with PBB Backbone Edge Bridge (BEB)
functions where it can encapsulate/de-encapsulate customer MAC frames
in provider B-MACs and perform I-SID translation if needed.
PBB PBB
BEB +----------+ BEB
| | | |
| +-----------+ | IP | +-----------+ |
| | MPLS | | MPLS | | MPLS | |
V | Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
Figure 7: H-VPLS with MPLS Access Network and PBB U-PE
The U-PE still provides the same type of services toward its
customers as before and they are:
- Port mode (either 802.1D, 802.1Q, or 802.1ad)
- VLAN mode (either 802.1Q or 802.1ad)
- VLAN-bundling mode (either 802.1Q or 802.1ad)
By incorporating a PBB function, the U-PE maps each of these services
(for a given customer) onto a single I-SID based on the configuration
at the U-PE. Many I-SIDs are multiplexed within a single bridge
domain (e.g. B-VLAN). The U-PE can then map a bridge domain onto a
VPLS instance and the encapsulated frames are sent over the PW
associated with that VPLS instance. Furthermore the entire Ethernet
bridging operation over the VPLS network is performed as defined in
[RFC4762]. In other words, MAC forwarding is based on the B-MAC
address space and service delimiter is based on VLAN ID, which is B-
VID in this case. There is no need to inspect or deal with I-SID
values in the VPLS N-PEs.
In the case of PBB U-PEs in a single I-SID domain, I-SID assignment
is performed globally across all MPLS access networks and therefore
there is no need for I-SID translation. This scenario support I-SID
bundling mode and it is assumed that the mapping of the I-SIDs to the
bridge domain (e.g., B-VLAN) is consistent across all the
participating PE devices. In the case of the I-SID bundling mode, a
bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and
existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type
is used as defined in [RFC4447] [RFC4448].
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I-SID mode can be considered as a degenerate case of I-SID bundling
where a single bridge domain is used per I-SID. However, that results
in an increased number of bridge domains and PWs in the PEs. PBB
flood containment (B-MAC multicast pruning) per I-SID can be used in
conjunction with I-SID bundling mode to limit the scope of flooding
per I-SID thus removing the need for I-SID mode.
6.2 H-VPLS with MPLS Access: PBB N-PE
In this case, the PBB function is incorporated at the N-PE to improve
the scalability of H-VPLS networks in terms of the numbers of MAC
addresses and service instances that are supported.
Customer networks or hosts (CE) connect into the U-PE nodes using
standard Ethernet interfaces [802.1D], [802.1Q], or [802.1ad]. The U-
PE is connected upstream to one or more VPLS N-PE nodes by MPLS PWs
(per customer). These, in turn, are connected via a full-mesh of PWs
(per customer or group of customers) traversing the IP/MPLS core.
The U-PE still provides the same type of services toward its
customers as before and they are:
- Port mode (either 802.1D, 802.1Q, or 802.1ad)
- VLAN mode (either 802.1Q or 802.1ad)
- VLAN-bundling mode (either 802.1Q or 802.1ad)
The spoke PW from the U-PE to the N-PE is not service multiplexed
because there is no PBB functionality on the U-PE - i.e. one service
per PW.
PBB PBB
BEB +----------+ BEB
| | | |
+-----------+ | | IP | | +-----------+
| MPLS | V | MPLS | V | MPLS |
| Access +----+ | Core | +----+ Access |
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| | | | | |
+-----------+ +----------+ +-----------+
Figure 8: H-VPLS with MPLS Access Network and PBB N-PE
By incorporating a PBB function, the N-PE maps each of these services
(for a given customer) onto a single I-SID based on the configuration
at the N-PE. Many I-SIDs can be multiplexed within a single bridge
domain (e.g. B-VLAN). The N-PE can, then, either map a single I-SID
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into a VPLS instance or it can map a bridge domain (e.g. B-VLAN) onto
a VPLS instance, according to its configuration. Next, the
encapsulated frames are sent over the set of PWs associated with that
VPLS instance.
In the case of PBB N-PEs in a single I-SID domain, I-SID assignment
is performed globally across all MPLS access networks and therefore
there is no need for I-SID translation. This scenario supports I-SID
bundling mode and it is assumed that the mapping of the I-SIDs to the
bridge domain (e.g., B-VLAN) is consistent across all the
participating PE devices. In the case of the I-SID bundling mode, a
bridge domain (e.g., B-VLAN) is mapped to a VPLS instance and
existing Ethernet raw mode (0x0005) or tagged mode (0x0004) PW type
as defined in [RFC4447] [RFC4448], can be used.
I-SID mode can be considered as a degenerate case of I-SID bundling
where a single bridge domain is used per I-SID. However, that results
in an increased number of bridge domains and PWs in the PE. PBB flood
containment (B-MAC multicast pruning) per I-SID can be used in
conjunction with I-SID bundling mode to limit the scope of flooding
per I-SID thus removing the need for I-SID mode.
7. H-VPLS with MPLS Access: PBB Migration Scenarios
Operators and service providers that have deployed H-VPLS with either
MPLS or Ethernet are unlikely to migrate to PBB technology overnight
because of obvious cost implications. Thus, it is imperative to
outline migration strategies that will allow operators to protect
investments in their installed base while still taking advantage of
the scalability benefits of PBB technology.
In the following sub-sections, we explore three different migration
scenarios which allow a mix of existing H-VPLS access networks to co-
exist with newer PBB-based access networks. The scenarios differ in
whether the Ethernet service frames passing over the VPLS core are
PBB-encapsulated or not. The first scenario in section 7.1 involves
passing only non PBB-encapsulated frames over the core. The second
scenario in section 7.2 stipulates passing only PBB-encapsulated
frames over the core. Whereas, the final scenario in section 7.3
depicts a core that supports a mix of PBB-encapsulated and non PBB-
encapsulated frames. The advantages and disadvantages of each
scenario will be discussed in its respective section.
7.1 802.1ad Service Frames over VPLS Core
In this scenario, existing access networks are left unchanged. All N-
PEs would forward frames based on C-MACs. In other words, Ethernet
frames which are traversing the VPLS core (within PWs) would use the
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802.1ad frame format, as in current VPLS. Hence, the N-PEs in
existing access networks do not require any modification. For new
MPLS access networks that have PBB functions on the U-PE, the
corresponding N-PE must incorporate built-in IB-BEB functions in
order to terminate the PBB encapsulation before the frames enter the
core. A key point here is that while both the U-PE and N-PE nodes
implement PBB IB-BEB functionality, the former has the I-Component
facing the customer (CE) and the B-Component facing the core; whereas
the latter has the I-Component facing the core and the B-Component
facing the customer (i.e. access network).
PBB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 9: Migration with 802.1ad Service Frames over VPLS Core
The main advantage of this approach is that it requires no change to
existing access networks or existing VPLS N-PEs. The main
disadvantage is that these N-PEs will not leverage the advantages of
PBB in terms of MAC address and PW scalability. It is worth noting
that this migration scenario is an optimal option for an H-VPLS
deployment with a single PBB-capable access network. When multiple
PBB-capable access networks are required, then the scenario in
Section 7.3 is preferred, as it provides a more scalable and optimal
interconnect amongst the PBB-capable networks.
7.2 PBB Service Frames over VPLS Core
This scenario requires that the VPLS N-PE connecting to existing MPLS
access networks be upgraded to incorporate IB-BEB functions. All
Ethernet service frames passing over the VPLS core would be PBB-
encapsulated. The PBB over MPLS access networks would require no
special requirements beyond what is captured in section 6 of this
document. In this case, both the U-PE and N-PE which implement IB-BEB
functionality have the I-Component facing the customer and the B-
Component facing the core.
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PBB PBB
IB-BEB +----------+ IB-BEB
| | | |
+-----------+ | | IP | +-----------+ |
| MPLS | V | MPLS | | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | | PE | |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 10: Migration with PBB Service Frames over VPLS Core
The main advantage of this approach is that it allows better
scalability of the VPLS N-PEs in terms of MAC address and pseudowire
counts. The disadvantage is that it requires upgrading the VPLS N-
PEs of all existing MPLS access networks.
7.3 Mixed 802.1ad and PBB over VPLS Core
In this scenario, existing access networks are left unchanged, and
exchange Ethernet frames with 802.1ad format over the PWs in the
core. The newly added access networks, which incorporate PBB
functionality exchange Ethernet frames that are PBB-encapsulated
amongst each other over core PWs. For service connectivity between
existing access network (non PBB capable) and new access network (PBB
based), the VPLS N-PE of the latter network employs IB-BEB
functionality to de-capsulate the PBB header from frames outbound to
the core, and encapsulate the PBB header for frames inbound from the
core. As a result, a mix of PBB-encapsulated and 802.1ad Ethernet
service frames are exchanged over the VPLS core.
This mode of operation requires new functionality on the VPLS N-PE of
the PBB-capable access network, so that the PE can send frames in
802.1ad format or PBB format, on a per PW basis, depending on the
capability of the destination access network. Effectively, the PE
would have to incorporate B-BEB as well as IB-BEB functions.
A given PE needs to be aware of the capability of its remote peer in
order to determine whether it connects to the right PW Forwarder.
This can be achieved either via static configuration, or by extending
the VPLS control plane (BGP-based auto-discovery and LDP Signaling)
discussed in [RFC6074]. The latter approach and the details of the
extensions required are out of scope for this document.
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PBB
B-BEB PBB
+----------+ IB-BEB IB-BEB
| | | |
+-----------+ | IP | | +-----------+ |
| MPLS | | MPLS | V | MPLS | |
| Access +----+ | Core | +----+ Access | V
+--+ +----+ |VPLS|-| |-|VPLS| +----+ +--+
|CE|--|U-PE| |N-PE| | | |N-PE| |U-PE|--|CE|
+--+ +----+ +----+ | | +----+ +----+ +--+
| (Existing)| | | | (New) |
+-----------+ +----------+ +-----------+
Figure 11: Migration with Mixed 802.1ad &PBB Service Frames
over VPLS Core
The U-PE and N-PE of the PBB-capable access network both employ BEB
functionality: The U-PE implements IB-BEB function where the I-
Component faces the customer (CE) and the B-Component faces the core.
The N-PE, on the other hand, implements IB-BEB functionality with the
I-Component facing the core and the B-Component facing the customer
(access network). In addition, the N-PE implements stand-alone B-BEB
functionality.
This scenario combines the advantages of both previous scenarios
without any of their shortcomings, namely: it does not require any
changes to existing access networks and it allows the N-PE to
leverage the scalability benefits of 802.1ah for PBBN to PBBN
connectivity. The disadvantage of this option is that it requires new
functionality on the N-PE of the PBBN access. A second disadvantage
is that this option requires two P2MP LSPs to be setup at the ingress
N-PE - one for the N-PEs that support PBB encapsulation and another
one for the N-PEs that don't support PBB encapsulation.
8. Acknowledgments
The authors would like to thank Chris Metz and Dinesh Mohan for their
valuable feedback and contributions.
9. IANA Considerations
This document has no actions for IANA.
10. Security Considerations
This document does not introduce any additional security aspects
beyond those applicable to VPLS/H-VPLS. VPLS/H-VPLS security
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considerations are already covered in [RFC4111] and [RFC4762].
11. References
11.1 Normative References
[802.1ad] "Virtual Bridged Local Area Networks, Amendment 4: Provider
Bridges", IEEE Std. 802.1ad-2005, May 2006
[802.1ah] "Virtual Bridged Local Area Networks Amendment 7: Provider
Backbone Bridges", IEEE Std. 802.1ah-2008, August 2008
[RFC4447] "Pseudowire Setup and Maintenance using LDP", RFC4447,
April 2006
[RFC4448] "Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC4448, April 2006
[RFC4762] "Virtual Private LAN Service (VPLS) Using Label
Distribution Protocol (LDP) Signaling", RFC4762, January 2007
[RFC6074] E. Rosen, et al., "Provisioning, Autodiscovery and
Signaling in L2VPNs", RFC6074, January 2011
11.2 Informative References
[802.1Q] "Virtual Bridged Local Area Networks", IEEE Std. 802.1Q-
2005
[802.1D-REV] "Media Access Control (MAC) Bridges", IEEE Std. 802.1D-
2003
[RFC6246] A. Sajassi, et al., "VPLS Interoperability with CE
Bridges", RFC6246, June 2011
[RFC4111] Fang, L., "Security Framework for Provider-Provisioned
Virtual Private Networks (PPVPNs)", RFC 4111, July 2005.
Authors' Addresses
Ali Sajassi
Cisco
Email: sajassi@cisco.com
Samer Salam
Cisco
Sajassi et al. Expires April 21, 2014 [Page 25]
INTERNET DRAFT VPLS Interoperability with PBB October 21, 2013
Email: ssalam@cisco.com
Nabil Bitar
Verizon Communications
Email : nabil.n.bitar@verizon.com
Florin Balus
Nuage Networks
Email: florin.balus@nuagenetworks.net
Sajassi et al. Expires April 21, 2014 [Page 26]
