PBB-EVPN
draft-ietf-l2vpn-pbb-evpn-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7623.
Expired & archived
|
|
|---|---|---|---|
| Authors | Ali Sajassi , Samer Salam , Sami Boutros , Dr. Nabil N. Bitar , Aldrin Isaac , Lizhong Jin | ||
| Last updated | 2012-12-22 (Latest revision 2012-06-20) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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| Send notices to | (None) |
draft-ietf-l2vpn-pbb-evpn-03
Internet Working Group Ali Sajassi
Internet Draft Samer Salam
Category: Standards Track Sami Boutros
Cisco
Florin Balus Nabil Bitar
Wim Henderickx Verizon
Alcatel-Lucent
Aldrin Isaac
Clarence Filsfils Bloomberg
Dennis Cai
Cisco Lizhong Jin
ZTE
Expires: December 20, 2012 June 20, 2012
PBB-EVPN
draft-ietf-l2vpn-pbb-evpn-03
Status of this Memo
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Copyright and License Notice
Copyright (c) 2012 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
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Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Abstract
This document discusses how Ethernet Provider Backbone Bridging
[802.1ah] can be combined with E-VPN in order to reduce the number of
BGP MAC advertisement routes by aggregating Customer/Client MAC (C-
MAC) addresses via Provider Backbone MAC address (B-MAC), provide
client MAC address mobility using C-MAC aggregation and B-MAC sub-
netting, confine the scope of C-MAC learning to only active flows,
offer per site policies and avoid C-MAC address flushing on topology
changes. The combined solution is referred to as PBB-EVPN.
Conventions
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. MAC Advertisement Route Scalability . . . . . . . . . . . 5
4.2. C-MAC Mobility with MAC Summarization . . . . . . . . . . 5
4.3. C-MAC Address Learning and Confinement . . . . . . . . . . 5
4.4. Per Site Policy Support . . . . . . . . . . . . . . . . . 6
4.5. Avoiding C-MAC Address Flushing . . . . . . . . . . . . . 6
5. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
6. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. BGP MAC Advertisement Route . . . . . . . . . . . . . . . 7
6.2. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . 7
6.3. Per VPN Route Targets . . . . . . . . . . . . . . . . . . 7
6.4. MAC Mobility Extended Community . . . . . . . . . . . . . 7
7. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. MAC Address Distribution over Core . . . . . . . . . . . . 8
7.2. Device Multi-homing . . . . . . . . . . . . . . . . . . . 8
7.2.1 Flow-based Load-balancing . . . . . . . . . . . . . . . 8
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7.2.1.1 MES B-MAC Address Assignment . . . . . . . . . . . 8
7.2.1.2. Automating B-MAC Address Assignment . . . . . . . 10
7.2.1.3 Split Horizon and Designated Forwarder Election . . 11
7.2.2 I-SID Based Load-balancing . . . . . . . . . . . . . . . 11
7.2.2.1 MES B-MAC Address Assignment . . . . . . . . . . . . 11
7.2.2.2 Split Horizon and Designated Forwarder Election . . 12
7.3. Network Multi-homing . . . . . . . . . . . . . . . . . . . 12
7.4. Frame Forwarding . . . . . . . . . . . . . . . . . . . . . 12
7.4.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . 12
7.4.2. Multicast/Broadcast . . . . . . . . . . . . . . . . . 13
8. Minimizing ARP Broadcast . . . . . . . . . . . . . . . . . . . 13
9. Seamless Interworking with IEEE 802.1aq/802.1Qbp . . . . . . . 13
9.1 B-MAC Address Assignment . . . . . . . . . . . . . . . . . . 14
9.2 IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route . . . . . 14
9.3 Operation: . . . . . . . . . . . . . . . . . . . . . . . . . 15
10. Solution Advantages . . . . . . . . . . . . . . . . . . . . . 15
10.1. MAC Advertisement Route Scalability . . . . . . . . . . . 15
10.2. C-MAC Mobility with MAC Sub-netting . . . . . . . . . . . 16
10.3. C-MAC Address Learning and Confinement . . . . . . . . . 16
10.4. Seamless Interworking with TRILL and 802.1aq Access
Networks . . . . . . . . . . . . . . . . . . . . . . . . 16
10.5. Per Site Policy Support . . . . . . . . . . . . . . . . . 17
10.6. Avoiding C-MAC Address Flushing . . . . . . . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
12. Security Considerations . . . . . . . . . . . . . . . . . . . 18
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
14. Intellectual Property Considerations . . . . . . . . . . . . 18
15. Normative References . . . . . . . . . . . . . . . . . . . . 18
16. Informative References . . . . . . . . . . . . . . . . . . . 18
17. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
[E-VPN] introduces a solution for multipoint L2VPN services, with
advanced multi-homing capabilities, using BGP for distributing
customer/client MAC address reach-ability information over the core
MPLS/IP network. [802.1ah] defines an architecture for Ethernet
Provider Backbone Bridging (PBB), where MAC tunneling is employed to
improve service instance and MAC address scalability in Ethernet as
well as VPLS networks [PBB-VPLS].
In this document, we discuss how PBB can be combined with E-VPN in
order to: reduce the number of BGP MAC advertisement routes by
aggregating Customer/Client MAC (C-MAC) addresses via Provider
Backbone MAC address (B-MAC), provide client MAC address mobility
using C-MAC aggregation and B-MAC sub-netting, confine the scope of
C-MAC learning to only active flows, offer per site policies and
avoid C-MAC address flushing on topology changes. The combined
solution is referred to as PBB-EVPN.
2. Contributors
In addition to the authors listed above, the following individuals
also contributed to this document.
Keyur Patel, Cisco
Sam Aldrin, Huawei
3. Terminology
BEB: Backbone Edge Bridge
B-MAC: Backbone MAC Address
CE: Customer Edge
C-MAC: Customer/Client MAC Address
DHD: Dual-homed Device
DHN: Dual-homed Network
LACP: Link Aggregation Control Protocol
LSM: Label Switched Multicast
MDT: Multicast Delivery Tree
MES: MPLS Edge Switch
MP2MP: Multipoint to Multipoint
P2MP: Point to Multipoint
P2P: Point to Point
PoA: Point of Attachment
PW: Pseudowire
E-VPN: Ethernet VPN
4. Requirements
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The requirements for PBB-EVPN include all the requirements for E-VPN
that were described in [EVPN-REQ], in addition to the following:
4.1. MAC Advertisement Route Scalability
In typical operation, an [E-VPN] MES sends a BGP MAC Advertisement
Route per customer/client MAC (C-MAC) address. In certain
applications, this poses scalability challenges, as is the case in
virtualized data center environments where the number of virtual
machines (VMs), and hence the number of C-MAC addresses, can be in
the millions. In such scenarios, it is required to reduce the number
of BGP MAC Advertisement routes by relying on a 'MAC summarization'
scheme, as is provided by PBB. Note that the MAC summarization
capability already built into E-VPN is not sufficient in those
environments, as will be discussed next.
4.2. C-MAC Mobility with MAC Summarization
Certain applications, such as virtual machine mobility, require
support for fast C-MAC address mobility. For these applications, it
is not possible to use MAC address summarization in E-VPN, i.e.
advertise reach-ability to a MAC address prefix. Rather, the exact
virtual machine MAC address needs to be transmitted in BGP MAC
Advertisement route. Otherwise, traffic would be forwarded to the
wrong segment when a virtual machine moves from one Ethernet segment
to another. This hinders the scalability benefits of summarization.
It is required to support C-MAC address mobility, while retaining the
scalability benefits of MAC summarization. This can be achieved by
leveraging PBB technology, which defines a Backbone MAC (B-MAC)
address space that is independent of the C-MAC address space, and
aggregate C-MAC addresses via a B-MAC address and then apply
summarization to B-MAC addresses.
4.3. C-MAC Address Learning and Confinement
In E-VPN, all the MES nodes participating in the same E-VPN instance
are exposed to all the C-MAC addresses learnt by any one of these MES
nodes because a C-MAC learned by one of the MES nodes is advertise in
BGP to other MES nodes in that E-VPN instance. This is the case even
if some of the MES nodes for that E-VPN instance are not involved in
forwarding traffic to, or from, these C-MAC addresses. Even if an
implementation does not install hardware forwarding entries for C-MAC
addresses that are not part of active traffic flows on that MES, the
device memory is still consumed by keeping record of the C-MAC
addresses in the routing table (RIB). In network applications with
millions of C-MAC addresses, this introduces a non-trivial waste of
MES resources. As such, it is required to confine the scope of
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visibility of C-MAC addresses only to those MES nodes that are
actively involved in forwarding traffic to, or from, these addresses.
4.4. Per Site Policy Support
In many applications, it is required to be able to enforce
connectivity policy rules at the granularity of a site (or segment).
This includes the ability to control which MES nodes in the network
can forward traffic to, or from, a given site. PBB-EVPN is capable of
providing this granularity of policy control. In the case where per
C-MAC address granularity is required, the EVI can always continue to
operate in E-VPN mode.
4.5. Avoiding C-MAC Address Flushing
It is required to avoid C-MAC address flushing upon link, port or
node failure for multi-homed devices and networks. This is in order
to speed up re-convergence upon failure.
5. Solution Overview
The solution involves incorporating IEEE 802.1ah Backbone Edge Bridge
(BEB) functionality on the E-VPN MES nodes similar to PBB-VPLS, where
BEB functionality is incorporated in the VPLS PE nodes. The MES
devices would then receive 802.1Q Ethernet frames from their
attachment circuits, encapsulate them in the PBB header and forward
the frames over the IP/MPLS core. On the egress E-VPN MES, the PBB
header is removed following the MPLS disposition, and the original
802.1Q Ethernet frame is delivered to the customer equipment.
BEB +--------------+ BEB
|| | | ||
\/ | | \/
+----+ AC1 +----+ | | +----+ +----+
| CE1|-----| | | | | |---| CE2|
+----+\ |MES1| | IP/MPLS | |MES3| +----+
\ +----+ | Network | +----+
\ | |
AC2\ +----+ | |
\| | | |
|MES2| | |
+----+ | |
/\ +--------------+
||
BEB
<-802.1Q-> <------PBB over MPLS------> <-802.1Q->
Figure 1: PBB-EVPN Network
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The MES nodes perform the following functions:- Learn customer/client
MAC addresses (C-MACs) over the attachment circuits in the data-
plane, per normal bridge operation.
- Learn remote C-MAC to B-MAC bindings in the data-plane from traffic
ingress from the core per [802.1ah] bridging operation.
- Advertise local B-MAC address reach-ability information in BGP to
all other MES nodes in the same set of service instances. Note that
every MES has a set of local B-MAC addresses that uniquely identify
the device. More on the MES addressing in section 5.
- Build a forwarding table from remote BGP advertisements received
associating remote B-MAC addresses with remote MES IP addresses and
the associated MPLS label(s).
6. BGP Encoding
PBB-EVPN leverages the same BGP Routes and Attributes defined in [E-
VPN], adapted as follows:
6.1. BGP MAC Advertisement Route
The E-VPN MAC Advertisement Route is used to distribute B-MAC
addresses of the MES nodes instead of the C-MAC addresses of end-
stations/hosts. This is because the C-MAC addresses are learnt in the
data-plane for traffic arriving from the core. The MAC Advertisement
Route is encoded as follows:
- The MAC address field contains the B-MAC address.
- The Ethernet Tag field is set to 0.
The route is tagged with the RT corresponding to the EVI associated
with the B-MAC address.
All other fields are set as defined in [E-VPN].
6.2. Ethernet Auto-Discovery Route
This route and all of its associated modes are not needed in PBB-
EVPN.
6.3. Per VPN Route Targets
PBB-EVPN uses the same set of route targets defined in [E-VPN]. The
future revision of this document will describe new RT types.
6.4. MAC Mobility Extended Community
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This extended community is a new transitive extended community. It
may be advertised along with the MAC Advertisement route. When used
in PBB-EVPN, it indicates that the C-MAC forwarding tables for the I-
SIDs associated with the RT tagging the MAC Advertisement route must
be flushed. This extended community is encoded in 8-bytes as follows:
- Type (1 byte) = Pending IANA assignment.
- Sub-Type (1 byte) = Pending IANA assignment.
- Reserved (2 bytes)
- Counter (4 bytes)
Note that all other BGP messages and/or attributes are used as
defined in [E-VPN].
7. Operation
This section discusses the operation of PBB-EVPN, specifically in
areas where it differs from [E-VPN].
7.1. MAC Address Distribution over Core
In PBB-EVPN, host MAC addresses (i.e. C-MAC addresses) need not be
distributed in BGP. Rather, every MES independently learns the C-MAC
addresses in the data-plane via normal bridging operation. Every MES
has a set of one or more unicast B-MAC addresses associated with it,
and those are the addresses distributed over the core in MAC
Advertisement routes.
7.2. Device Multi-homing
7.2.1 Flow-based Load-balancing
This section describes the procedures for supporting device multi-
homing in an all-active redundancy model with flow-based load-
balancing.
7.2.1.1 MES B-MAC Address Assignment
In [802.1ah] every BEB is uniquely identified by one or more B-MAC
addresses. These addresses are usually locally administered by the
Service Provider. For PBB-EVPN, the choice of B-MAC address(es) for
the MES nodes must be examined carefully as it has implications on
the proper operation of multi-homing. In particular, for the scenario
where a CE is multi-homed to a number of MES nodes with all-active
redundancy and flow-based load-balancing, a given C-MAC address would
be reachable via multiple MES nodes concurrently. Given that any
given remote MES will bind the C-MAC address to a single B-MAC
address, then the various MES nodes connected to the same CE must
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share the same B-MAC address. Otherwise, the MAC address table of the
remote MES nodes will keep oscillating between the B-MAC addresses of
the various MES devices. For example, consider the network of Figure
1, and assume that MES1 has B-MAC BM1 and MES2 has B-MAC BM2. Also,
assume that both links from CE1 to the MES nodes are part of an all-
active multi-chassis Ethernet link aggregation group. If BM1 is not
equal to BM2, the consequence is that the MAC address table on MES3
will keep oscillating such that the C-MAC address CM of CE1 would
flip-flop between BM1 or BM2, depending on the load-balancing
decision on CE1 for traffic destined to the core.
Considering that there could be multiple sites (e.g. CEs) that are
multi-homed to the same set of MES nodes, then it is required for all
the MES devices in a Redundancy Group to have a unique B-MAC address
per site. This way, it is possible to achieve fast convergence in the
case where a link or port failure impacts the attachment circuit
connecting a single site to a given MES.
+---------+
+-------+ MES1 | IP/MPLS |
/ | |
CE1 | Network | MESr
M1 \ | |
+-------+ MES2 | |
/-------+ | |
/ | |
CE2 | |
M2 \ | |
\ | |
+------+ MES3 +---------+
Figure 2: B-MAC Address Assignment
In the example network shown in Figure 2 above, two sites
corresponding to CE1 and CE2 are dual-homed to MES1/MES2 and
MES2/MES3, respectively. Assume that BM1 is the B-MAC used for the
site corresponding to CE1. Similarly, BM2 is the B-MAC used for the
site corresponding to CE2. On MES1, a single B-MAC address (BM1) is
required for the site corresponding to CE1. On MES2, two B-MAC
addresses (BM1 and BM2) are required, one per site. Whereas on MES3,
a single B-MAC address (BM2) is required for the site corresponding
to CE2. All three MES nodes would advertise their respective B-MAC
addresses in BGP using the MAC Advertisement routes defined in [E-
VPN]. The remote MES, MESr, would learn via BGP that BM1 is reachable
via MES1 and MES2, whereas BM2 is reachable via both MES2 and MES3.
Furthermore, MESr establishes via the normal bridge learning that C-
MAC M1 is reachable via BM1, and C-MAC M2 is reachable via BM2. As a
result, MESr can load-balance traffic destined to M1 between MES1 and
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MES2, as well as traffic destined to M2 between both MES2 and MES3.
In the case of a failure that causes, for example, CE1 to be isolated
from MES1, the latter can withdraw the route it has advertised for
BM1. This way, MESr would update its path list for BM1, and will send
all traffic destined to M1 over to MES2 only.
For single-homed sites, it is possible to assign a unique B-MAC
address per site, or have all the single-homed sites connected to a
given MES share a single B-MAC address. The advantage of the first
model over the second model is the ability to avoid C-MAC destination
address lookup on the disposition PE (even though source C-MAC
learning is still required in the data-plane). Also, by assigning the
B-MAC addresses from a contiguous range, it is possible to advertise
a single B-MAC subnet for all single-homed sites, thereby rendering
the number of MAC advertisement routes required at par with the
second model.
In summary, every MES may use a unicast B-MAC address shared by all
single-homed CEs or a unicast B-MAC address per single-homed CE and,
in addition, a unicast B-MAC address per dual-homed CE. In the latter
case, the B-MAC address MUST be the same for all MES nodes in a
Redundancy Group connected to the same CE.
7.2.1.2. Automating B-MAC Address Assignment
The MES B-MAC address used for single-homed sites can be
automatically derived from the hardware (using for e.g. the
backplane's address). However, the B-MAC address used for multi-homed
sites must be coordinated among the RG members. To automate the
assignment of this latter address, the MES can derive this B-MAC
address from the MAC Address portion of the CE's LACP System
Identifier by flipping the 'Locally Administered' bit of the CE's
address. This guarantees the uniqueness of the B-MAC address within
the network, and ensures that all MES nodes connected to the same
multi-homed CE use the same value for the B-MAC address.
Note that with this automatic provisioning of the B-MAC address
associated with multi-homed CEs, it is not possible to support the
uncommon scenario where a CE has multiple bundles towards the MES
nodes, and the service involves hair-pinning traffic from one bundle
to another. This is because the split-horizon filtering relies on B-
MAC addresses rather than Site-ID Labels (as will be described in the
next section). The operator must explicitly configure the B-MAC
address for this fairly uncommon service scenario.
Whenever a B-MAC address is provisioned on the MES, either manually
or automatically (as an outcome of CE auto-discovery), the MES MUST
transmit an MAC Advertisement Route for the B-MAC address with a
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downstream assigned MPLS label that uniquely identifies that address
on the advertising MES. The route is tagged with the RTs of the
associated EVIs as described above.
7.2.1.3 Split Horizon and Designated Forwarder Election
[E-VPN] relies on access split horizon, where the Ethernet Segment
Label is used for egress filtering on the attachment circuit in order
to prevent forwarding loops. In PBB-EVPN, the B-MAC source address
can be used for the same purpose, as it uniquely identifies the
originating site of a given frame. As such, Segment Labels are not
used in PBB-EVPN, and the egress split-horizon filtering is done
based on the B-MAC source address. It is worth noting here that
[802.1ah] defines this B-MAC address based filtering function as part
of the I-Component options, hence no new functions are required to
support split-horizon beyond what is already defined in [802.1ah].
Given that the Segment label is not used in PBB-EVPN, the MES sets
the Label field in the Ethernet Segment Route to 0.
The Designated Forwarder election procedures are defined in [I-D-
Segment-Route].
7.2.2 I-SID Based Load-balancing
This section describes the procedures for supporting device multi-
homing in an all-active redundancy model with per-ISID load-
balancing.
7.2.2.1 MES B-MAC Address Assignment
In the case where per-ISID load-balancing is desired among the MES
nodes in a given redundancy group, multiple unicast B-MAC addresses
are allocated per multi-homed Ethernet Segment: Each MES connected to
the multi-homed segment is assigned a unique B-MAC. Every MES then
advertises its B-MAC address using the BGP MAC advertisement route.
A remote MES initially floods traffic to a destination C-MAC address,
located in a given multi-homed Ethernet Segment, to all the MES nodes
connected to that segment. Then, when reply traffic arrives at the
remote MES, it learns (in the data-path) the B-MAC address and
associated next-hop MES to use for said C-MAC address. When a MES
connected to a multi-homed Ethernet Segment loses connectivity to the
segment, due to link or port failure, it withdraws the B-MAC route
previously advertised for that segment. This causes the remote MES
nodes to flush all C-MAC addresses associated with the B-MAC in
question. This is done across all I-SIDs that are mapped to the EVI
of the withdrawn MAC route.
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7.2.2.2 Split Horizon and Designated Forwarder Election The procedures
are similar to the flow-based load-balancing case, with the only
difference being that the DF filtering must be applied to unicast as
well as multicast traffic, and in both core-to-segment as well as
segment-to-core directions.
7.3. Network Multi-homing
When an Ethernet network is multi-homed to a set of MES nodes running
PBB-EVPN, an all-active redundancy model can be supported with per
service instance (i.e. I-SID) load-balancing. In this model, DF
election is performed to ensure that a single MES node in the
redundancy group is responsible for forwarding traffic associated
with a given I-SID. This guarantees that no forwarding loops are
created. Filtering based on DF state applies to both unicast and
multicast traffic, and in both access-to-core as well as core-to-
access directions (unlike the multi-homed device scenario where DF
filtering is limited to multi-destination frames in the core-to-
access direction). Similar to the multi-homed device scenario, with
I-SID based load-balancing, a unique B-MAC address is assigned to
each of the MES nodes connected to the multi-homed network (Segment).
7.4. Frame Forwarding
The frame forwarding functions are divided in between the Bridge
Module, which hosts the [802.1ah] Backbone Edge Bridge (BEB)
functionality, and the MPLS Forwarder which handles the MPLS
imposition/disposition. The details of frame forwarding for unicast
and multi-destination frames are discussed next.
7.4.1. Unicast
Known unicast traffic received from the AC will be PBB-encapsulated
by the MES using the B-MAC source address corresponding to the
originating site. The unicast B-MAC destination address is determined
based on a lookup of the C-MAC destination address (the binding of
the two is done via transparent learning of reverse traffic). The
resulting frame is then encapsulated with an LSP tunnel label and the
MPLS label which uniquely identifies the B-MAC destination address on
the egress MES. If per flow load-balancing over ECMPs in the MPLS
core is required, then a flow label is added as the end of stack
label.
For unknown unicast traffic, the MES forwards these frames over MPLS
core. When these frames are to be forwarded, then the same set of
options used for forwarding multicast/broadcast frames (as described
in next section) are used.
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7.4.2. Multicast/Broadcast
Multi-destination frames received from the AC will be PBB-
encapsulated by the MES using the B-MAC source address corresponding
to the originating site. The multicast B-MAC destination address is
selected based on the value of the I-SID as defined in [802.1ah]. The
resulting frame is then forwarded over the MPLS core using one out of
the following two options:
Option 1: the MPLS Forwarder can perform ingress replication over a
set of MP2P tunnel LSPs. The frame is encapsulated with a tunnel LSP
label and the E-VPN ingress replication label advertised in the
Inclusive Multicast Route.
Option 2: the MPLS Forwarder can use P2MP tunnel LSP per the
procedures defined in [E-VPN]. This includes either the use of
Inclusive or Aggregate Inclusive trees.
Note that the same procedures for advertising and handling the
Inclusive Multicast Route defined in [E-VPN] apply here.
8. Minimizing ARP Broadcast
The MES nodes implement an ARP-proxy function in order to minimize
the volume of ARP traffic that is broadcasted over the MPLS network.
This is achieved by having each MES node snoop on ARP request and
response messages received over the access interfaces or the MPLS
core. The MES builds a cache of IP / MAC address bindings from these
snooped messages. The MES then uses this cache to respond to ARP
requests ingress on access ports and targeting hosts that are in
remote sites. If the MES finds a match for the IP address in its ARP
cache, it responds back to the requesting host and drops the request.
Otherwise, if it does not find a match, then the request is flooded
over the MPLS network using either ingress replication or LSM.
9. Seamless Interworking with IEEE 802.1aq/802.1Qbp
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+--------------+
| |
+---------+ | MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
|SW1 |--| | |MES1| |MES2| | |--| SW3|
+----+ | 802.1aq |---| | | |--| 802.1aq | +----+
+----+ | .1Qbp | +----+ +----+ | .1Qbp | +----+
|SW2 |--| | | Backbone | | |--| SW4|
+----+ +---------+ +--------------+ +---------+ +----+
|<------ IS-IS -------->|<-----BGP----->|<------ IS-IS ------>| CP
|<------------------------- PBB -------------------------->| DP
|<----MPLS----->|
Legend: CP = Control Plane View
DP = Data Plane View
Figure 7: Interconnecting 802.1aq/802.1Qbp Networks with PBB-EVPN
9.1 B-MAC Address Assignment
For the same reasons cited in the TRILL section, the B-MAC addresses
need to be globally unique across all the IEEE 802.1aq / 802.1Qbp
networks. The same hierarchical address assignment scheme depicted
above is proposed for B-MAC addresses as well.
9.2 IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route
B-MAC addresses associated with 802.1aq / 802.1Qbp switches are
advertised using the BGP MAC Advertisement route already defined in
[E-VPN].
The encapsulation for the transport of PBB frames over MPLS is
similar to that of classical Ethernet, albeit with the additional PBB
header, as shown in the figure below:
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+------------------+
| IP/MPLS Header |
+------------------+
| PBB Header |
+------------------+
| Ethernet Header |
+------------------+
| Ethernet Payload |
+------------------+
| Ethernet FCS |
+------------------+
Figure 8: PBB over MPLS Encapsulation
9.3 Operation:
When a MES receives a PBB-encapsulated Ethernet frame from the access
side, it performs a lookup on the B-MAC destination address to
identify the next hop. If the lookup yields that the next hop is a
remote MES, the local MES would then encapsulate the PBB frame in
MPLS. The label stack comprises of the VPN label (advertised by the
remote PE), followed by an LSP/IGP label. From that point onwards,
regular MPLS forwarding is applied.
On the disposition MES, assuming penultimate-hop-popping is employed,
the MES receives the MPLS-encapsulated PBB frame with a single label:
the VPN label. The value of the label indicates to the disposition
MES that this is a PBB frame, so the label is popped, the TTL field
(in the 802.1Qbp F-Tag) is reinitialized and normal PBB processing is
employed from this point onwards.
10. Solution Advantages
In this section, we discuss the advantages of the PBB-EVPN solution
in the context of the requirements set forth in section 3 above.
10.1. MAC Advertisement Route Scalability
In PBB-EVPN the number of MAC Advertisement Routes is a function of
the number of segments (sites), rather than the number of
hosts/servers. This is because the B-MAC addresses of the MESes,
rather than C-MAC addresses (of hosts/servers) are being advertised
in BGP. And, as discussed above, there's a one-to-one mapping between
multi-homed segments and B-MAC addresses, whereas there's a one-to-
one or many-to-one mapping between single-homed segments and B-MAC
addresses for a given MES. As a result, the volume of MAC
Advertisement Routes in PBB-EVPN is multiple orders of magnitude less
than E-VPN.
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10.2. C-MAC Mobility with MAC Sub-netting
In PBB-EVPN, if a MES allocates its B-MAC addresses from a contiguous
range, then it can advertise a MAC prefix rather than individual 48-
bit addresses. It should be noted that B-MAC addresses can easily be
assigned from a contiguous range because MES nodes are within the
provider administrative domain; however, CE devices and hosts are
typically not within the provider administrative domain. The
advantage of such MAC address sub-netting can be maintained even as
C-MAC addresses move from one Ethernet segment to another. This is
because the C-MAC address to B-MAC address association is learnt in
the data-plane and C-MAC addresses are not advertised in BGP. To
illustrate how this compares to E-VPN, consider the following
example:
If a MES running E-VPN advertises reachability for a MAC subnet that
spans N addresses via a particular segment, and then 50% of the MAC
addresses in that subnet move to other segments (e.g. due to virtual
machine mobility), then in the worst case, N/2 additional MAC
Advertisement routes need to be sent for the MAC addresses that have
moved. This defeats the purpose of the sub-netting. With PBB-EVPN, on
the other hand, the sub-netting applies to the B-MAC addresses which
are statically associated with MES nodes and are not subject to
mobility. As C-MAC addresses move from one segment to another, the
binding of C-MAC to B-MAC addresses is updated via data-plane
learning.
10.3. C-MAC Address Learning and Confinement
In PBB-EVPN, C-MAC address reachability information is built via
data-plane learning. As such, MES nodes not participating in active
conversations involving a particular C-MAC address will purge that
address from their forwarding tables. Furthermore, since C-MAC
addresses are not distributed in BGP, MES nodes will not maintain any
record of them in control-plane routing table.
10.4. Seamless Interworking with TRILL and 802.1aq Access Networks
Consider the scenario where two access networks, one running MPLS and
the other running 802.1aq, are interconnected via an MPLS backbone
network. The figure below shows such an example network.
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+--------------+
| |
+---------+ | MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | |MES1| |MES2| | |--| CE |
+----+ | 802.1aq |---| | | |--| MPLS | +----+
+----+ | | +----+ +----+ | | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 9: Interoperability with 802.1aq
If the MPLS backbone network employs E-VPN, then the 802.1aq data-
plane encapsulation must be terminated on MES1 or the edge device
connecting to MES1. Either way, all the MES nodes that are part of
the associated service instances will be exposed to all the C-MAC
addresses of all hosts/servers connected to the access networks.
However, if the MPLS backbone network employs PBB-EVPN, then the
802.1aq encapsulation can be extended over the MPLS backbone, thereby
maintaining C-MAC address transparency on MES1. If PBB-EVPN is also
extended over the MPLS access network on the right, then C-MAC
addresses would be transparent to MES2 as well.
Interoperability with TRILL access network will be described in
future revision of this draft.
10.5. Per Site Policy Support
In PBB-EVPN, a unique B-MAC address can be associated with every site
(single-homed or multi-homed). Given that the B-MAC addresses are
sent in BGP MAC Advertisement routes, it is possible to define per
site (i.e. B-MAC) forwarding policies including policies for E-TREE
service.
10.6. Avoiding C-MAC Address Flushing
With PBB-EVPN, it is possible to avoid C-MAC address flushing upon
topology change affecting a multi-homed device. To illustrate this,
consider the example network of Figure 1. Both MES1 and MES2
advertize the same B-MAC address (BM1) to MES3. MES3 then learns the
C-MAC addresses of the servers/hosts behind CE1 via data-plane
learning. If AC1 fails, then MES3 does not need to flush any of the
C-MAC addresses learnt and associated with BM1. This is because MES1
will withdraw the MAC Advertisement routes associated with BM1,
thereby leading MES3 to have a single adjacency (to MES2) for this B-
MAC address. Therefore, the topology change is communicated to MES3
and no C-MAC address flushing is required.
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11. Acknowledgements
TBD.
12. Security Considerations
There are no additional security aspects beyond those of VPLS/H-VPLS
that need to be discussed here.
13. IANA Considerations
This document requires IANA to assign a new SAFI value for L2VPN_MAC
SAFI.
14. Intellectual Property Considerations
This document is being submitted for use in IETF standards
discussions.
15. Normative References
[802.1ah] "Virtual Bridged Local Area Networks Amendment 7: Provider
Backbone Bridges", IEEE Std. 802.1ah-2008, August 2008.
16. Informative References
[PBB-VPLS] Sajassi et al., "VPLS Interoperability with Provider
Backbone Bridges", draft-ietf-l2vpn-vpls-pbb-interop-
02.txt, work in progress, July, 2011.
[EVPN-REQ] Sajassi et al., "Requirements for Ethernet VPN (E-VPN)",
draft-sajassi-raggarwa-l2vpn-evpn-req-01.txt, work in
progress, July, 2011.
[E-VPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
l2vpn-evpn-00.txt, work in progress, February, 2012.
17. Authors' Addresses
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
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Samer Salam
Cisco
595 Burrard Street, Suite 2123
Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
Sami Boutros
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sboutros@cisco.com
Nabil Bitar
Verizon Communications
Email : nabil.n.bitar@verizon.com
Aldrin Isaac
Bloomberg
Email: aisaac71@bloomberg.net
Florin Balus
Alcatel-Lucent
701 E. Middlefield Road
Mountain View, CA, USA 94043
Email: florin.balus@alcatel-lucent.com
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.be
Clarence Filsfils
Cisco
Email: cfilsfil@cisco.com
Dennis Cai
Cisco
Email: dcai@cisco.com
Lizhong Jin
ZTE Corporation
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889, Bibo Road
Shanghai, 201203, China
Email: lizhong.jin@zte.com.cn
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