One document matched: draft-sajassi-l2vpn-pbb-evpn-00.txt
Internet Working Group Ali Sajassi
Internet Draft Samer Salam
Category: Standards Track Cisco
Expires: September 7, 2011 March 7, 2011
PBB E-VPN
draft-sajassi-l2vpn-pbb-evpn-00.txt
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Sajassi, et. al. [Page 1]
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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, provide Customer MAC address
mobility with MAC sub-netting, provide Customer MAC address scoping,
offer per site policies and avoid Customer 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.................................................... 3
2. Terminology..................................................... 3
3. Requirements.................................................... 3
3.1. MAC Advertisement Route Scalability........................... 3
3.2. C-MAC Mobility with MAC Sub-netting........................... 4
3.3. C-MAC Address Scoping......................................... 4
3.4. Per Site Policy Support....................................... 4
3.5. Avoiding C-MAC Address Flushing............................... 5
4. Solution Overview............................................... 5
5. BGP Encoding.................................................... 6
5.1. BGP MAC Advertisement Route................................... 6
5.2. Ethernet Auto-Discovery Route................................. 6
5.3. Per VPN Route Targets......................................... 7
6. Operation....................................................... 7
6.1. MAC Address Distribution over Core............................ 7
6.2. Device Multi-homing........................................... 7
6.2.1. MES MAC Layer Addressing & Multi-homing..................... 7
6.2.2. Split Horizon and Designated Forwarder Election............ 10
6.3. Frame Forwarding............................................. 10
6.3.1. Unicast.................................................... 10
6.3.2. Multicast/Broadcast........................................ 11
7. Acknowledgements............................................... 11
8. Security Considerations........................................ 11
9. IANA Considerations............................................ 11
10. Intellectual Property Considerations.......................... 11
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11. Normative References.......................................... 11
12. Informative References........................................ 11
13. Authors' Addresses............................................ 12
1.
Introduction
[E-VPN] introduces a solution for multipoint L2VPN services with
advanced multi-homing capabilities using BGP for distributing
customer 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 networks.
In this document, we discuss how PBB can be combined with E-VPN in
order to reduce the number of BGP MAC advertisement routes, provide
Customer MAC address mobility with MAC sub-netting, provide Customer
MAC address scoping, offer per site policies and avoid Customer MAC
address flushing on topology changes. The combined solution is
referred to as PBB-EVPN.
2.
Terminology
BEB: Backbone Edge Bridge
B-MAC: Backbone MAC Address
CE: Customer Edge
C-MAC: Customer 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
3.
Requirements
The requirements for PBB-EVPN include all the requirements for E-VPN
that were described in [EVPN-REQ], in addition to the following:
3.1.
MAC Advertisement Route Scalability
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In typical operation, an [E-VPN] MES sends a BGP MAC Advertisement
Route per customer 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 sub-netting capability already
built into E-VPN is not sufficient in those environments, as will be
discussed next.
3.2.
C-MAC Mobility with MAC Sub-netting
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 sub-netting 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 sub-netting.
It is required to support C-MAC address mobility, while retaining
the scalability benefits of MAC sub-netting. 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.
3.3.
C-MAC Address Scoping
In E-VPN, all the MES nodes participating in the same EVI are
exposed to all the C-MAC addresses learnt by any one of these MES
nodes. This is the case even if the MES in question is not involved
in forwarding traffic to, or from, these C-MAC addresses. Even if an
implementation doesn't 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 control-plane. 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
visibility of C-MAC addresses only to those MES nodes that are
actively involved in forwarding traffic to, or from, these
addresses.
3.4.
Interworking with TRILL and 802.1aq Access Networks with
C-MAC Address Transparency
[TRILL] and [802.1aq] define next generation Ethernet bridging
technologies that offer optimal forwarding using IS-IS control
plane, and C-MAC address transparency via Ethernet tunneling
technologies. When access networks based on TRILL or 802.1aq are
interconnected over an MPLS/IP network, it is required to guarantee
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C-MAC address transparency on the hand-off point and the edge (i.e.
MES) of the MPLS network. As such, solutions that require
termination of the access data-plane encapsulation (i.e. TRILL or
802.1ah) at the hand-off to the MPLS network do not meet this
transparency requirement, and expose the MPLS edge devices to the
MAC address scalability problem.
PBB-EVPN supports seamless interconnect with these next generation
Ethernet solutions while guaranteeing C-MAC address transparency on
the MES nodes.
3.5.
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.
3.6.
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.
4.
Solution Overview
The solution involves incorporating IEEE 802.1ah Backbone Edge
Bridge (BEB) functionality on the E-VPN MES 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| | |
+----+ | |
/\ +--------------+
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||
BEB
<-802.1Q-> <------PBB over MPLS------> <-802.1Q->
Figure 1: PBB-EVPN Network
The MES nodes perform the following functions:
- Learn customer 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.
- 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.
5.
BGP Encoding
PBB-EVPN leverages the same BGP Routes and Attributes defined in [E-
VPN], adapted as follows:
5.1.
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 RD is set to a Type 1 RD RD [RFC4364]. The value field encodes
the IP address of the MES (typically, the loopback address) followed
by 0. The reason for such encoding is that the RD cannot be that of
a single EVI since the same B-MAC address can span across multiple
EVIs.
-The MAC address field contains the B-MAC address.
-The Ethernet Tag field is set to 0.
The route is tagged with the set of RTs corresponding to all EVIs
associated with the B-MAC address.
All other fields are set as defined in [E-VPN].
5.2.
Ethernet Auto-Discovery Route
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The Ethernet A-D Route is used in PBB-EVPN to advertise reach-
ability of Ethernet segments. The route is encoded as follows:
-The RD is set to a Type 1 RD RD [RFC4364]. The value field encodes
the IP address of the MES (typically, the loopback address) followed
by 0. The reason for such encoding is that the RD cannot be that of
a single EVI since the same Ethernet segment can be associated with
multiple EVIs.
-The Ethernet Tag field is always set to 0.
-The MPLS label is downstream assigned and identifies the Ethernet
segment (i.e. B-MAC address) on the advertising MES.
The Ethernet A-D Route is tagged with the set of RTs corresponding
to all EVIs associated with the B-MAC address.
All other fields are set as defined in [E-VPN].
5.3.
Per VPN Route Targets
PBB-EVPN uses the same set of route targets defined in [E-VPN]. More
specifically, the RT associated with a VPN is set to the value of
the I-SID associated with the service instance. This eliminates the
need for manually configuring the VPN-RT.
Note that all other BGP messages and/or attributes are used as
defined in [E-VPN].
6.
Operation
This section discusses the operation of PBB-EVPN, specifically in
areas where it differs from [E-VPN].
6.1.
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. Given that these B-MAC addresses are global
within the provider's network, there is no need to advertise them on
a per service instance basis.
6.2.
Device Multi-homing
6.2.1.
MES MAC Layer Addressing & Multi-homing
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
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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 share the same B-MAC address. Otherwise, the MAC
address table of the remote MES nodes will keep flip-flopping
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
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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 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 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.
6.2.1.1.
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 mult-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.
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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
downstream assigned MPLS label that uniquely identifies the address
on the advertising MES. The route is tagged with the RTs of the
associated EVIs as described above.
6.2.2.
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 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 remain unchanged from
[E-VPN].
6.3.
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.
6.3.1.
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 can optionally forward these
frames over MPLS core; however, the default is not to forward. If
these frames are to be forwarded, then the same set of options used
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for forwarding multicast/broadcast frames (as described in next
section) are used.
6.3.2.
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 an LSP
tunnel label and the E-VPN ingress replication label advertised in
the Inclusive Multicast Route.
Option 2: the MPLS Forwarder can use P2MP LSM tunnel 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.
7.
Acknowledgements
TBD.
8.
Security Considerations
There are no additional security aspects beyond those of VPLS/H-VPLS
that need to be discussed here.
9.
IANA Considerations
This document requires IANA to assign a new SAFI value for L2VPN_MAC
SAFI.
10.
Intellectual Property Considerations
This document is being submitted for use in IETF standards
discussions.
11.
Normative References
[802.1ah] "Virtual Bridged Local Area Networks Amendment 7: Provider
Backbone Bridges", IEEE Std. 802.1ah-2008, August 2008.
12.
Informative References
Sajassi, et al. [Page 11]
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[EVPN-REQ] Sajassi et al., "Requirements for Ethernet VPN (E-VPN)",
draft-sajassi-raggarwa-l2vpn-evpn-req-00.txt, work in progress,
October, 2010.
[E-VPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-
raggarwa-sajassi-l2vpn-evpn-01.txt, November, 2010.
, work in progress, June, 2010.
13.
Authors' Addresses
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
Samer Salam
Cisco
595 Burrard Street, Suite 2123
Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
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