Internet DRAFT - draft-sajassi-l2vpn-pbb-evpn
draft-sajassi-l2vpn-pbb-evpn
Internet Working Group Ali Sajassi
Internet Draft Samer Salam
Category: Standards Track Sami Boutros
Cisco
Florin Balus
Wim Henderickx Nabil Bitar
Alcatel-Lucent Verizon
Clarence Filsfils Aldrin Issac
Dennis Cai Bloomberg
Cisco
Lizhong Jin
ZTE
Expires: April 28, 2012 October 28, 2011
PBB E-VPN
draft-sajassi-l2vpn-pbb-evpn-03.txt
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.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on April 28, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Sajassi, et. al. [Page 1]
draft-sajassi-l2vpn-pbb-evpn-03.txt
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
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.................................................... 3
2. Contributors.................................................... 4
3. Terminology..................................................... 4
4. Requirements.................................................... 4
4.1. MAC Advertisement Route Scalability........................... 4
4.2. C-MAC Mobility with MAC Sub-netting........................... 5
4.3. C-MAC Address Learning and Confinement........................ 5
4.4. Interworking with TRILL and 802.1aq Access Networks with C-MAC
Address Transparency............................................... 5
4.5. Per Site Policy Support....................................... 6
4.6. 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................................. 8
6.3. Per VPN Route Targets......................................... 8
6.4. MAC Mobility Extended Community............................... 8
Sajassi, et al. [Page 2]
draft-sajassi-l2vpn-pbb-evpn-03.txt
7. Operation....................................................... 8
7.1. MAC Address Distribution over Core............................ 8
7.2. Device Multi-homing........................................... 8
7.2.1. MES MAC Layer Addressing & Multi-homing..................... 8
7.2.2. Split Horizon and Designated Forwarder Election............ 11
7.3. Network Multi-homing......................................... 11
7.3.1. B-MAC Address Advertisement................................ 12
7.3.2. Failure Handling........................................... 12
7.4. Frame Forwarding............................................. 13
7.4.1. Unicast.................................................... 13
7.4.2. Multicast/Broadcast........................................ 14
8. Minimizing ARP Broadcast....................................... 14
9. Seamless Interworking with TRILL and IEEE 802.1aq/802.1Qbp..... 14
9.1. TRILL Nickname Advertisement Route........................... 15
9.2. IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route............ 16
9.3. Operation.................................................... 16
10. Solution Advantages........................................... 17
10.1. MAC Advertisement Route Scalability......................... 18
10.2. C-MAC Mobility with MAC Sub-netting......................... 18
10.3. C-MAC Address Learning and Confinement...................... 18
10.4. Interworking with TRILL and 802.1aq Access Networks with C-MAC
Address Transparency.............................................. 18
10.5. Per Site Policy Support..................................... 19
10.6. Avoiding C-MAC Address Flushing............................. 19
11. Acknowledgements.............................................. 20
12. Security Considerations....................................... 20
13. IANA Considerations........................................... 20
14. Intellectual Property Considerations.......................... 20
15. Normative References.......................................... 20
16. Informative References........................................ 20
17. Authors' Addresses............................................ 20
1.
Introduction
[E-VPN] introduces a solution for multipoint L2VPN services with
advanced multi-homing capabilities using BGP for distributing
customer/clinent 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 and in VPLS networks [PBB-VPLS].
Sajassi, et al. [Page 3]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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
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
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'
Sajassi, et al. [Page 4]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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.
4.2.
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, and
aggregate C-MAC addresses via a B-MAC address and then apply sub-
netting 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 visibility of C-MAC addresses only
to those MES nodes that are actively involved in forwarding traffic
to, or from, these addresses.
4.4.
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
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
Sajassi, et al. [Page 5]
draft-sajassi-l2vpn-pbb-evpn-03.txt
802.1aq) 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.
4.5.
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.
4.6.
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.
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 PEs (PBB-VPLS) where BEB functionality is incorporated in 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| | |
+----+ | |
/\ +--------------+
||
Sajassi, et al. [Page 6]
draft-sajassi-l2vpn-pbb-evpn-03.txt
BEB
<-802.1Q-> <------PBB over MPLS------> <-802.1Q->
Figure 1: PBB-EVPN Network
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 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].
Sajassi, et al. [Page 7]
draft-sajassi-l2vpn-pbb-evpn-03.txt
6.2.
Ethernet Auto-Discovery Route
This route and any of its associated modes is not needed in PBB-
EVPN.
6.3.
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.
6.4.
MAC Mobility Extended Community
This extended community is a new transitive extended community. It
may be advertised along with MAC Advertisement routes. When used in
PBB-EVPN, it indicates that the C-MAC forwarding tables for the I-
SIDs associated with the RTs tagging the MAC Advertisement routes
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. Given that these B-MAC addresses are global
within the provider's network, there's no need to advertise them on
a per service instance basis.
7.2.
Device Multi-homing
7.2.1.
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
Sajassi, et al. [Page 8]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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 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,
Sajassi, et al. [Page 9]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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 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.
7.2.1.1.
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
Sajassi, et al. [Page 10]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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
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.
7.2.2.
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].
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, a unique B-MAC address
is used on the MES per multi-homed network (Segment). This helps
eliminate the need for C-MAC address flushing in all but one failure
scenario (more details on this in the Failure Handling section
below). The B-MAC address may be auto-provisioned by snooping on the
BPDUs of the multi-homed network: the B-MAC address is set to the
root bridge ID of the CIST albeit with the 'Locally Administered'
bit set.
Sajassi, et al. [Page 11]
draft-sajassi-l2vpn-pbb-evpn-03.txt
7.3.1.
B-MAC Address Advertisement
For every multi-homed network, the MES advertises two MAC
Advertisement routes with different RDs and identical MAC addresses
and ESIs. One of these routes will be tagged with a lower Local Pref
attribute than the other. The route with the higher Local Pref will
be tagged with the RTs corresponding to the I-SIDs for which the
advertising MES is the DF. Whereas, the route with the lower Local
Pref will be tagged with the RTs corresponding to the I-SIDs for
which the advertising MES is the backup DF. Consider the example
network of the figure below, where a multi-homed network (MHN1) is
connected to two MES nodes (MES1 and MES2).
+---------+
+-------+ MES1 | IP/MPLS |
+------+ BM1 | |
| | | Network | MESr
| MHN1 | BM1 | |
+------+ +-------+ MES2 | |
+---------+
Figure 3: Multi-homed Network
Both MES nodes use the same B-MAC address (BM1) for the Ethernet
Segment (ESI1) associated with MHN1. Assume, for instance, that MES1
is the DF for the even I-SIDs whereas MES2 is the DF for the odd I-
SIDs. In this example, the routes advertised by MES1 and MES2 would
be as follows:
MES1:
Route 1: RD11, BM1, ESI1, Local Pref = 120, RT2, RT4, RT6...
Route 2: RD12, BM1, ESI1, Local Pref = 80, RT1, RT3, RT5...
MES2:
Route 1: RD21, BM1, ESI1, Local Pref = 120, RT1, RT3, RT5...
Route 2: RD22, BM1, ESI1, Local Pref = 80, RT2, RT4, RT6
Upon receiving the above MAC Advertisement routes, the remote MES
nodes (e.g. MESr) would install forwarding entries for BM1 towards
MES1 for the even I-SIDs, and towards MES2 for the odd I-SIDs.
It is worth noting that the procedures of this section can also be
used for a multi-homed device in order to support all-active
redundancy with per I-SID load-balancing.
7.3.2.
Failure Handling
In the case of an MES node failure, or when the MES is isolated from
the multi-homed network due to a port or link failure, the affected
Sajassi, et al. [Page 12]
draft-sajassi-l2vpn-pbb-evpn-03.txt
MES withdraws its MAC Advertisement routes for the associated B-MAC.
This serves as a trigger for the remote MES nodes to adjust their
forwarding entries to point to the backup DF. Because the same B-MAC
address is used on both the DF and backup DF nodes, then there is no
need to flush the C-MAC address table upon the occurrence of these
failures.
In the case where the multi-homed network is partitioned, the MES
nodes can detect this condition by snooping on the network's BPDUs.
When a MES detects that the root bridge ID has changed, it must
change the value of the B-MAC address associated with the Ethernet
Segment. This is done by the MES withdrawing the previous MAC
Advertisement route, and advertising a new route for the updated B-
MAC. The MES, which detects the failure, must inform the remote MES
nodes to flush their C-MAC address tables for the affected I-SIDs.
This is required because when the multi-homed network is
partitioned, certain C-MAC addresses will move from being associated
with the old B-MAC address to the new B-MAC addresses. Other C-MAC
addresses will have their reachability remaining intact. Given that
the MES node has no means of identifying which C-MACs have moved and
which have not, the entire C-MAC forwarding table for the affected
I-SIDs must be flushed. The affected MES signals the need for the C-
MAC flushing by sending the MAC Mobility Extended Community in the
MP_UNREACH_NLRI attribute containing the E-VPN NLRI for the
withdrawn MAC Advertisement route.
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
Sajassi, et al. [Page 13]
draft-sajassi-l2vpn-pbb-evpn-03.txt
options used for forwarding multicast/broadcast frames (as described
in next section) are used.
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 TRILL and IEEE 802.1aq/802.1Qbp
PBB-EVPN enables seamless connectivity of TRILL or 802.1aq/802.1Qbp
networks over an MPLS/IP core while maintaining control-plane
separation among these networks. We will refer to one or any of
TRILL, 802.1aq or 802.1Qbp networks collectively as 'NG-Ethernet
networks' thereafter.
Every NG-Ethernet network that is connected to the MPLS core runs an
independent instance of the corresponding IS-IS control-plane. Each
MES participates in the NG-Ethernet network control plane of its
local site. The MES peers, in IS-IS protocol, with the switches
internal to the site, but does not terminate the TRILL / PBB data-
Sajassi, et al. [Page 14]
draft-sajassi-l2vpn-pbb-evpn-03.txt
plane encapsulation. So, from a control-plane viewpoint, the MES
appears as an edge switch; whereas, from a data-plane viewpoint, the
MES appears as a core switch to the NG-Ethernet network.
The MES nodes encapsulate TRILL / PBB frames with MPLS in the
imposition path, and de-capsulate them in the disposition path.
9.1.
TRILL Nickname Advertisement Route
A new BGP route is defined to support the interconnection of TRILL
networks over PBB-EVPN: the TRILL Nickname Advertisement' route,
encoded as follows:
+---------------------------------------+
| RD (8 octets) |
+---------------------------------------+
|Ethernet Segment Identifier (10 octets)|
+---------------------------------------+
| Ethernet Tag ID (4 octets) |
+---------------------------------------+
| Nickname Length (1 octet) |
+---------------------------------------+
| RBridge Nickname (2 octets) |
+---------------------------------------+
| MPLS Label (n * 3 octets) |
+---------------------------------------+
Figure 4: TRILL Nickname Advertisement Route
The MES uses this route to advertise the reachability of TRILL
RBridge nicknames to other MES nodes in the VPN instance. The MPLS
label advertised in this route can be allocated on a per VPN basis
and serves the purpose of identifying to the disposition MES that
the MPLS-encapsulated packet holds an MPLS encapsulated TRILL frame.
The encapsulation for the transport of TRILL frames over MPLS is
encoded as shown in the figure below:
+------------------+
| IP/MPLS Header |
+------------------+
| TRILL Header |
+------------------+
| Ethernet Header |
+------------------+
| Ethernet Payload |
+------------------+
| Ethernet FCS |
+------------------+
Figure 5: TRILL over MPLS Encapsulation
Sajassi, et al. [Page 15]
draft-sajassi-l2vpn-pbb-evpn-03.txt
It is worth noting here that while it is possible to transport
Ethernet encapsulated TRILL frames over MPLS, that approach
unnecessarily wastes 16 bytes per packet. That approach further
requires either the use of well-known MAC addresses or having the
MES nodes advertise in BGP their device MAC addresses, in order to
resolve the TRILL next-hop L2 adjacency. To that end, it is simpler
and more efficient to transport TRILL natively over MPLS and that is
why we are defining the above BGP route for TRILL Nickname
advertisement.
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:
+------------------+
| IP/MPLS Header |
+------------------+
| PBB Header |
+------------------+
| Ethernet Header |
+------------------+
| Ethernet Payload |
+------------------+
| Ethernet FCS |
+------------------+
Figure 6: PBB over MPLS Encapsulation
9.3.
Operation
For correct connectivity, the TRILL Nicknames or 802.1aq/802.1Qbp B-
MACs must be globally unique in the network. This can be achieved,
for instance, by using a hierarchical Nickname (or B-MAC) assignment
paradigm, and encoding a Site ID in the high-order bits of the
Nickname (or B-MAC):
Nickname (or B-MAC) = [Site ID : Rbridge ID (or MAC)]
The only practical difference between TRILL Nicknames and B-MACs, in
this regards, is with respect to the size of the address space:
Nicknames are 16-bits wide whereas B-MACs are 48-bits wide.
Sajassi, et al. [Page 16]
draft-sajassi-l2vpn-pbb-evpn-03.txt
Every MES then advertises (in BGP) the Nicknames (or B-MACs) of all
switches local to its site in the TRILL Nickname Advertisement
routes (or MAC Advertisement routes).
Furthermore, the MES advertises in IS-IS (to the local island) the
Rbridge nicknames (or B-MACs) of all remote switches in all the
other TRILL (or IEEE 802.1aq/802.1Qbp) islands that the MES has
learned via BGP.
Note that by having multiple MES nodes (connected to the same TRILL
or 802.1aq /802.1Qbp island) advertise routes to the same RBridge
nickname (or B-MAC), with equal BGP Local_Pref attribute, it is
possible to perform active/active load-balancing to/from the MPLS
core.
When a MES receives an Ethernet-encapsulated TRILL frame from the
access side, it removes the Ethernet encapsulation (i.e. outer MAC
header), and performs a lookup on the egress RBridge nickname in the
TRILL header to identify the next-hop. If the lookup yields that the
next hop is a remote MES, the local MES would then encapsulate the
TRILL frame in MPLS. The label stack comprises of the VPN label
(advertised by the remote MES), 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 TRILL frame with a
single label: the VPN label. The value of the label indicates to the
disposition MES that this is a TRILL packet, so the label is popped,
the TTL field (in the TRILL header) is reinitialized and normal
TRILL processing is employed from this point onwards.
By the same token, 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.
Sajassi, et al. [Page 17]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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.
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
Sajassi, et al. [Page 18]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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.
+--------------+
| |
+---------+ | MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | |MES1| |MES2| | |--| CE |
+----+ | 802.1aq |---| | | |--| MPLS | +----+
+----+ | | +----+ +----+ | | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 7: 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 MES2. MES2 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,
Sajassi, et al. [Page 19]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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.
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-00.txt, work in
progress, September, 2011.
[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.
17.
Authors' Addresses
Ali Sajassi
Cisco
170 West Tasman Drive
San Jose, CA 95134, US
Email: sajassi@cisco.com
Samer Salam
Sajassi, et al. [Page 20]
draft-sajassi-l2vpn-pbb-evpn-03.txt
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
889, Bibo Road
Shanghai, 201203, China
Email: lizhong.jin@zte.com.cn
Sajassi, et al. [Page 21]
