Internet DRAFT - draft-ietf-l2vpn-pbb-evpn
draft-ietf-l2vpn-pbb-evpn
Internet Working Group Ali Sajassi, Ed.
Internet Draft Samer Salam
Category: Standards Track Cisco
Nabil Bitar
Verizon
Aldrin Isaac
Bloomberg
Wim Henderickx
Alcatel-Lucent
Expires: November 14, 2015 May 14, 2015
Provider Backbone Bridging Combined with Ethernet VPN (PBB-EVPN)
draft-ietf-l2vpn-pbb-evpn-10
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Abstract
This document discusses how Ethernet Provider Backbone Bridging (PBB)
can be combined with Ethernet VPN (EVPN) 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, 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. MAC Advertisement Route Scalability . . . . . . . . . . . 5
4.2. C-MAC Mobility Independent of B-MAC Advertisements . . . . 5
4.3. C-MAC Address Learning and Confinement . . . . . . . . . . 6
4.4. Per Site Policy Support . . . . . . . . . . . . . . . . . 6
4.5. No C-MAC Address Flushing for All-Active Multi-Homing . . 6
5. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 6
6. BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Ethernet Auto-Discovery Route . . . . . . . . . . . . . . 7
6.2. MAC/IP Advertisement Route . . . . . . . . . . . . . . . . 8
6.3. Inclusive Multicast Ethernet Tag Route . . . . . . . . . . 8
6.4. Ethernet Segment Route . . . . . . . . . . . . . . . . . . 9
6.5. ESI Label Extended Community . . . . . . . . . . . . . . . 9
6.6. ES-Import Route Target . . . . . . . . . . . . . . . . . . 9
6.7. MAC Mobility Extended Community . . . . . . . . . . . . . 9
6.8. Default Gateway Extended Community . . . . . . . . . . . . 9
7. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. MAC Address Distribution over Core . . . . . . . . . . . . 10
7.2. Device Multi-homing . . . . . . . . . . . . . . . . . . . 10
7.2.1. Flow-based Load-balancing . . . . . . . . . . . . . . . 10
7.2.1.1. PE B-MAC Address Assignment . . . . . . . . . . . 10
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7.2.1.2. Automating B-MAC Address Assignment . . . . . . . 12
7.2.1.3 Split Horizon and Designated Forwarder Election . . 12
7.2.2. I-SID Based Load-balancing . . . . . . . . . . . . . . 13
7.2.2.1. PE B-MAC Address Assignment . . . . . . . . . . . . 13
7.2.2.2. Split Horizon and Designated Forwarder Election . . 13
7.2.2.3. Handling Failure Scenarios . . . . . . . . . . . . 13
7.3. Network Multi-homing . . . . . . . . . . . . . . . . . . . 14
7.4. Frame Forwarding . . . . . . . . . . . . . . . . . . . . . 15
7.4.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . 15
7.4.2. Multicast/Broadcast . . . . . . . . . . . . . . . . . 15
7.5. MPLS Encapsulation of PBB Frames . . . . . . . . . . . . . 16
8. Minimizing ARP/ND Broadcast . . . . . . . . . . . . . . . . . 16
9. Seamless Interworking with IEEE 802.1aq/802.1Qbp . . . . . . . 17
9.1. B-MAC Address Assignment . . . . . . . . . . . . . . . . . 17
9.2. IEEE 802.1aq / 802.1Qbp B-MAC Address Advertisement . . . 17
9.4. Operation: . . . . . . . . . . . . . . . . . . . . . . . . 17
10. Solution Advantages . . . . . . . . . . . . . . . . . . . . . 18
10.1. MAC Advertisement Route Scalability . . . . . . . . . . . 18
10.2. C-MAC Mobility Independent of B-MAC Advertisements . . . 18
10.3. C-MAC Address Learning and Confinement . . . . . . . . . 19
10.4. Seamless Interworking with 802.1aq Access Networks . . . 19
10.5. Per Site Policy Support . . . . . . . . . . . . . . . . . 20
10.6. No C-MAC Address Flushing for All-Active Multi-Homing . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
12. Security Considerations . . . . . . . . . . . . . . . . . . . 20
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
14. Normative References . . . . . . . . . . . . . . . . . . . . 21
15. Informative References . . . . . . . . . . . . . . . . . . . 21
16. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
[RFC7432] 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. [PBB] 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 [RFC7080].
In this document, we discuss how PBB can be combined with EVPN 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, 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.
Lizhong Jin, ZTE
Sami Boutros, Cisco
Dennis Cai, Cisco
Keyur Patel, Cisco
Sam Aldrin, Huawei
Himanshu Shah, Ciena
Jorge Rabadan, ALU
3. Terminology
ARP: Address Resolution Protocol
BEB: Backbone Edge Bridge
B-MAC: Backbone MAC Address
CE: Customer Edge
C-MAC: Customer/Client MAC Address
ES: Ethernet Segment
ESI: Ethernet Segment Identifier
LSP: Label Switched Path
MP2MP: Multipoint to Multipoint
MP2P: Multipoint to Point
ND: Neighbor Discovery
NA: Neighbor Advertisement
P2MP: Point to Multipoint
P2P: Point to Point
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PE: Provider Edge
EVPN: Ethernet VPN
EVI: EVPN Instance
RT: Route Target
Single-Active Redundancy Mode: When only a single PE, among a group
of PEs attached to an Ethernet segment, is allowed to forward traffic
to/from that Ethernet Segment, then the Ethernet segment is defined
to be operating in Single-Active redundancy mode.
All-Active Redundancy Mode: When all PEs attached to an Ethernet
segment are allowed to forward traffic to/from that Ethernet Segment,
then the Ethernet segment is defined to be operating in All-Active
redundancy mode.
4. Requirements
The requirements for PBB-EVPN include all the requirements for EVPN
that were described in [RFC7209], in addition to the following:
4.1. MAC Advertisement Route Scalability
In typical operation, an EVPN PE 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 data center
interconnect (DCI) scenarios 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.
4.2. C-MAC Mobility Independent of B-MAC Advertisements
Certain applications, such as virtual machine mobility, require
support for fast C-MAC address mobility. For these applications, when
using EVPN, the 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 means MAC address prefixes cannot be used in
data center applications.
In order to support C-MAC address mobility, while retaining the
scalability benefits of MAC summarization, PBB technology is used. It
defines a Backbone MAC (B-MAC) address space that is independent of
the C-MAC address space, and aggregates C-MAC addresses via a single
B-MAC address.
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4.3. C-MAC Address Learning and Confinement
In EVPN, all the PE nodes participating in the same EVPN instance are
exposed to all the C-MAC addresses learnt by any one of these PE
nodes because a C-MAC learned by one of the PE nodes is advertise in
BGP to other PE nodes in that EVPN instance. This is the case even if
some of the PE nodes for that EVPN 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 PE, 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
PE resources. As such, it is required to confine the scope of
visibility of C-MAC addresses only to those PE 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 PE nodes in the network
can forward traffic to, or from, a given site. Both EVPN and PBB-EVPN
are capable of providing this granularity of policy control. In the
case where the policy needs to be at the granularity of per C-MAC
address, then C-MAC address learning in control-plane (in BGP) per
[RFC7432] should be used.
4.5. No C-MAC Address Flushing for All-Active Multi-Homing
Just as in [RFC7432], it is required to avoid C-MAC address flushing
upon link, port or node failure for All-Active multi-homed segments.
5. Solution Overview
The solution involves incorporating IEEE Backbone Edge Bridge (BEB)
functionality on the EVPN PE nodes similar to PBB-VPLS, where BEB
functionality is incorporated in the VPLS PE nodes. The PE 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 EVPN PE, the PBB header is
removed following the MPLS disposition, and the original 802.1Q
Ethernet frame is delivered to the customer equipment.
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BEB +--------------+ BEB
|| | | ||
\/ | | \/
+----+ AC1 +----+ | | +----+ +----+
| CE1|-----| | | | | |---| CE2|
+----+\ | PE1| | IP/MPLS | | PE3| +----+
\ +----+ | Network | +----+
\ | |
AC2\ +----+ | |
\| | | |
| PE2| | |
+----+ | |
/\ +--------------+
||
BEB
<-802.1Q-> <------PBB over MPLS------> <-802.1Q->
Figure 1: PBB-EVPN Network
The PE 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 for traffic
received from the core per [PBB] bridging operation.
- Advertise local B-MAC address reach-ability information in BGP to
all other PE nodes in the same set of service instances. Note that
every PE has a set of B-MAC addresses that uniquely identify the
device. B-MAC address assignment is described in details in section
7.2.2.
- Build a forwarding table from remote BGP advertisements received
associating remote B-MAC addresses with remote PE IP addresses and
the associated MPLS label(s).
6. BGP Encoding
PBB-EVPN leverages the same BGP Routes and Attributes defined in
[RFC7432], adapted as follows:
6.1. Ethernet Auto-Discovery Route
This route and all of its associated modes are not needed in PBB-EVPN
because PBB encapsulation provides the required level of indirection
for C-MAC addresses - i.e., an ES can be represented by a B-MAC
address for the purpose of data-plane learning/forwarding.
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The receiving PE knows that it need not wait for the receipt of the
Ethernet A-D route for route resolution by means of the reserved
Ethernet Segment Identifier (ESI) encoded in the MAC Advertisement
route: the ESI values of 0 and MAX-ESI indicate that the receiving PE
can resolve the path without an Ethernet A-D route.
6.2. MAC/IP Advertisement Route
The EVPN MAC/IP Advertisement Route is used to distribute B-MAC
addresses of the PE 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 Ethernet Segment Identifier field must be set either to 0 (for
single-homed segments or multi-homed segments with per-ISID load-
balancing) or to MAX-ESI (for multi-homed segments with per-flow
load-balancing). All other values are not permitted.
- All other fields are set as defined in [RFC7432].
This route is tagged with the Route Target (RT) corresponding to its
EVI. This EVI is analogous to a B-VID.
6.3. Inclusive Multicast Ethernet Tag Route
This route is used for multicast pruning per I-SID. It is used for
auto-discovery of PEs participating in a given I-SID so that a
multicast tunnel (MP2P, P2P, P2MP, or MP2MP LSP) can be setup for
that I-SID . [RFC7080] uses multicast pruning per I-SID based on
[MMRP] which is a soft-state protocol. The advantages of multicast
pruning using this BGP route over [MMRP] are that a) it scales very
well for large number of PEs and b) it works with any type of LSP
(MP2P, P2P, P2MP, or MP2MP); whereas, [MMRP] only works over P2P
pseudowires. The Inclusive Multicast Ethernet Tag Route is encoded as
follow:
- The Ethernet Tag field is set with the appropriate I-SID value.
- All other fields are set as defined in [RFC7432].
This route is tagged with an RT. This RT SHOULD be set to a value
corresponding to its EVI (which is analogous to a B-VID). The RT for
this route MAY also be auto-derived from the corresponding Ethernet
Tag (I-SID) based on the procedure specified in section 5.1.2.1 of
[OVERLAY].
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6.4. Ethernet Segment Route
This route is auto-discovery of member PEs belonging to a given
redundancy group (e.g., attached to a given Ethernet Segment) per
[RFC7432].
6.5. ESI Label Extended Community
This extended community is not used in PBB-EVPN. In [RFC7432], this
extended community is used along with the Ethernet AD route to
advertise an MPLS label for the purpose of split-horizon filtering.
Since in PBB-EVPN, the split-horizon filtering is performed natively
using B-MAC SA, there is no need for this extended community.
6.6. ES-Import Route Target
This RT is used as defined in [RFC7432].
6.7. MAC Mobility Extended Community
This extended community is defined in [RFC7432] and it is used with a
MAC route (B-MAC route in case of PBB-EVPN). The B-MAC route is
tagged with the RT corresponding to its EVI (which is analogous to a
B-VID). When this extended community is used along with a B-MAC route
in PBB-EVPN, it indicates that all C-MAC addresses associated with
that B-MAC address across all corresponding I-SIDs must be flushed.
When a PE first advertises a B-MAC, it MAY advertise it with this
Extended Community where the sticky/static flag is set to 1 and the
sequence number is set to zero. In such cases where the PE wants to
signal the stickiness of a B-MAC, then when a flush indication is
needed, the PE advertises the B-MAC along with the MAC Mobility
extended community where the sticky/static flag remains set and the
sequence number is incremented.
6.8. Default Gateway Extended Community
This extended community is not used in PBB-EVPN.
7. Operation
This section discusses the operation of PBB-EVPN, specifically in
areas where it differs from [RFC7432].
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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 PE independently learns the C-MAC
addresses in the data-plane via normal bridging operation. Every PE
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 mode (i.e., flow-based load-
balancing).
7.2.1.1. PE B-MAC Address Assignment
In [PBB] 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 PE 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 PE nodes with All-Active
redundancy mode, a given C-MAC address would be reachable via
multiple PE nodes concurrently. Given that any given remote PE will
bind the C-MAC address to a single B-MAC address, then the various PE
nodes connected to the same CE must share the same B-MAC address.
Otherwise, the MAC address table of the remote PE nodes will keep
oscillating between the B-MAC addresses of the various PE devices.
For example, consider the network of Figure 1, and assume that PE1
has B-MAC BM1 and PE2 has B-MAC BM2. Also, assume that both links
from CE1 to the PE nodes are part of the same Ethernet link
aggregation group. If BM1 is not equal to BM2, the consequence is
that the MAC address table on PE3 will keep oscillating such that the
C-MAC address M1 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 PE nodes, then it is required for all
the PE 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 PE.
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+---------+
+-------+ PE1 | IP/MPLS |
/ | |
CE1 | Network | PEr
M1 \ | |
+-------+ PE2 | |
/-------+ | |
/ | |
CE2 | |
M2 \ | |
\ | |
+------+ PE3 +---------+
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 PE1/PE2 and PE2/PE3,
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 PE1, a single B-MAC address (BM1) is
required for the site corresponding to CE1. On PE2, two B-MAC
addresses (BM1 and BM2) are required, one per site. Whereas on PE3, a
single B-MAC address (BM2) is required for the site corresponding to
CE2. All three PE nodes would advertise their respective B-MAC
addresses in BGP using the MAC Advertisement routes defined in
[RFC7432]. The remote PE, PEr, would learn via BGP that BM1 is
reachable via PE1 and PE2, whereas BM2 is reachable via both PE2 and
PE3. Furthermore, PEr establishes, via the PBB bridge learning
procedure, that C-MAC M1 is reachable via BM1, and C-MAC M2 is
reachable via BM2. As a result, PEr can load-balance traffic destined
to M1 between PE1 and PE2, as well as traffic destined to M2 between
both PE2 and PE3. In the case of a failure that causes, for example,
CE1 to be isolated from PE1, the latter can withdraw the route it has
advertised for BM1. This way, PEr would update its path list for BM1,
and will send all traffic destined to M1 over to PE2 only.
For Single-Homed or Single-Active sites, it is possible to assign a
unique B-MAC address per site, or have all the Single-Homed sites or
Single-Active sites connected to a given PE 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). The disadvantage of the first model over the
second model is additional B-MAC advertisements in BGP.
In summary, every PE may use a unicast B-MAC address shared by all
single-homed sites or a unicast B-MAC address per single-homed site
and, in addition, a unicast B-MAC address per All-Active multi-homed
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site. In the latter case, the B-MAC address MUST be the same for all
PE nodes in a Redundancy Group connected to the same site.
7.2.1.2. Automating B-MAC Address Assignment
The PE B-MAC address used for Single-Homed or Single-Active sites can
be automatically derived from the hardware (using for e.g. the
backplane's address and/or PE's reserved MAC pool ). However, the B-
MAC address used for All-Active sites must be coordinated among the
RG members. To automate the assignment of this latter address, the PE
can derive this B-MAC address from the MAC Address portion of the
CE's Link Aggregation Control Protocol (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 PE nodes connected to the same All-Active CE use
the same value for the B-MAC address.
Note that with this automatic provisioning of the B-MAC address
associated with All-Active CEs, it is not possible to support the
uncommon scenario where a CE has multiple link bundles within the
same LACP session towards the PE 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 PE, either manually or
automatically (as an outcome of CE auto-discovery), the PE 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 PE. The route is tagged with the RTs of the
associated EVIs as described above.
7.2.1.3 Split Horizon and Designated Forwarder Election
[RFC7432] 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, Ethernet Segment (ES)
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 [PBB] 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 [PBB].
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The Designated Forwarder election procedures are defined in
[RFC7432].
7.2.2. I-SID Based Load-balancing
This section describes the procedures for supporting device multi-
homing in a Single-Active redundancy mode with per-ISID load-
balancing.
7.2.2.1. PE B-MAC Address Assignment
In the case where per-ISID load-balancing is desired among the PE
nodes in a given redundancy group, multiple unicast B-MAC addresses
are allocated per multi-homed Ethernet Segment: Each PE connected to
the multi-homed segment is assigned a unique B-MAC. Every PE then
advertises its B-MAC address using the BGP MAC advertisement route.
In this mode of operation, two B-MAC address assignment models are
possible:
- The PE may use a shared B-MAC address for multiple Ethernet
Segments (ES's). This includes the single-homed segments as well as
the multi-homed segments operating with per-ISID load-balancing mode.
- The PE may use a dedicated B-MAC address for each ES operating with
per-ISID load-balancing mode.
A PE implementation MAY choose to support either the shared B-MAC
address model or the dedicated B-MAC address model without causing
any interoperability issues.
A remote PE initially floods traffic to a destination C-MAC address,
located in a given multi-homed Ethernet Segment, to all the PE nodes
configured with that I-SID. Then, when reply traffic arrives at the
remote PE, it learns (in the data-path) the B-MAC address and
associated next-hop PE to use for said C-MAC address.
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.
7.2.2.3. Handling Failure Scenarios
When a PE connected to a multi-homed Ethernet Segment loses
connectivity to the segment, due to link or port failure, it needs to
notify the remote PEs to trigger C-MAC address flushing. This can be
achieved in one of two ways, depending on the B-MAC assignment model:
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- If the PE uses a shared B-MAC address for multiple ES's, then the
C-MAC flushing is signaled by means of having the failed PE re-
advertise the MAC Advertisement route for the associated B-MAC,
tagged with the MAC Mobility Extended Community attribute. The value
of the Counter field in that attribute must be incremented prior to
advertisement. This causes the remote PE 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.
- If the PE uses a dedicated B-MAC address for each Ethernet Segment
operating under per-ISID load-balancing mode, the failed PE simply
withdraws the B-MAC route previously advertised for that segment.
This causes the remote PE 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.
When a PE connected to a multi-homed Ethernet Segment fails (i.e.
node failure) or when the PE becomes completely isolated from the
EVPN network, the remote PEs will start purging the MAC Advertisement
routes that were advertised by the failed PE. This is done either as
an outcome of the remote PEs detecting that the BGP session to the
failed PE has gone down, or by having a Route Reflector withdrawing
all the routes that were advertised by the failed PE. The remote PEs,
in this case, will perform C-MAC address flushing as an outcome of
the MAC Advertisement route withdrawals.
For all failure scenarios (link/port failure, node failure and PE
node isolation), when the fault condition clears, the recovered PE
re-advertises the associated Ethernet Segment route to other members
of its Redundancy Group. This triggers the backup PE(s) in the
Redundancy Group to block the I-SIDs for which the recovered PE is a
DF. When a backup PE blocks the I-SIDs, it triggers a C-MAC address
flush notification to the remote PEs by re-advertising the MAC
Advertisement route for the associated B-MAC, with the MAC Mobility
Extended Community attribute. The value of the Counter field in that
attribute must be incremented prior to advertisement. This causes the
remote PE 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/readvertised MAC route.
7.3. Network Multi-homing
When an Ethernet network is multi-homed to a set of PE nodes running
PBB-EVPN, Single-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 PE node in the
redundancy group is responsible for forwarding traffic associated
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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 just like Single-Active multi-homed device scenario
(but unlike All-Active multi-homed device scenario where DF filtering
is limited to multi-destination frames in the core-to-access
direction). Similar to Single-Active multi-homed device scenario,
with I-SID based load-balancing, a unique B-MAC address is assigned
to each of the PE 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 [PBB] 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 PE 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 PE. If per flow load-balancing over ECMPs in the MPLS core
is required, then a flow label is added below the label associated
with the BMAC address in the label stack.
For unknown unicast traffic, the PE 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.
7.4.2. Multicast/Broadcast
Multi-destination frames received from the AC will be PBB-
encapsulated by the PE 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 [PBB]. 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 or P2P tunnel LSPs. The frame is encapsulated with a
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tunnel LSP label and the EVPN ingress replication label advertised in
the Inclusive Multicast Route.
Option 2: the MPLS Forwarder can use P2MP tunnel LSP per the
procedures defined in [RFC7432]. This includes either the use of
Inclusive or Aggregate Inclusive trees. Furthermore, the MPLS
Forwarder can use MP2MP tunnel LSP if Inclusive trees are used.
Note that the same procedures for advertising and handling the
Inclusive Multicast Route defined in [RFC7432] apply here.
7.5. MPLS Encapsulation of PBB Frames
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 8: PBB over MPLS Encapsulation
8. Minimizing ARP/ND Broadcast
The PE nodes MAY implement an ARP/ND-proxy function in order to
minimize the volume of ARP/ND traffic that is broadcasted over the
MPLS network. In case of ARP proxy, this is achieved by having each
PE node snoop on ARP request and response messages received over the
access interfaces or the MPLS core. The PE builds a cache of IP / MAC
address bindings from these snooped messages. The PE then uses this
cache to respond to ARP requests ingress on access ports and
targeting hosts that are in remote sites. If the PE 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 P2MP LSPs. In case of ND proxy, this is
achieved similar to the above but with ND/NA messages per [RFC4389].
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9. Seamless Interworking with IEEE 802.1aq/802.1Qbp
+--------------+
| |
+---------+ | MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
|SW1 |--| | | PE1| | PE2| | |--| 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
The B-MAC addresses need to be globally unique across all networks
including PBB-EVPN and IEEE 802.1aq / 802.1Qbp networks. The B-MAC
addresses used for Single-Home and Single-Active Ethernet Segments
should be unique because they are typically auto-derived from PE's
pools of reserved MAC addresses that are unique. The B-MAC addresses
used for All-Active Ethernet Segments should also be unique given
that each network operator typically has its own assigned
Organizationally Unique Identifier (OUI) and thus can assign its own
unique MAC addresses.
9.2. IEEE 802.1aq / 802.1Qbp B-MAC Address Advertisement
B-MAC addresses associated with 802.1aq / 802.1Qbp switches are
advertised using the EVPN MAC/IP route advertisement already defined
in [RFC7432].
9.4. Operation:
When a PE 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
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remote PE, the local PE 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 PE, assuming penultimate-hop-popping is employed,
the PE receives the MPLS-encapsulated PBB frame with a single label:
the VPN label. The value of the label indicates to the disposition PE
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 Ethernet Segments (e.g., sites), rather than the number
of hosts/servers. This is because the B-MAC addresses of the PEs,
rather than C-MAC addresses (of hosts/servers) are being advertised
in BGP. As discussed above, there's a one-to-one mapping between All-
Active multi-homed segments and their associated B-MAC addresses, and
there can be either a one-to-one or many-to-one mapping between
Single-Active multi-homed segments and their associated B-MAC
addresses, and finally there is a many-to-one mapping between single-
home sites and their associated B-MAC addresses on a given PE. This
means a single B-MAC is associated with one or more segments where
each segment can be associated with many C-MAC addresses. As a
result, the volume of MAC Advertisement Routes in PBB-EVPN may be
multiple orders of magnitude less than EVPN.
10.2. C-MAC Mobility Independent of B-MAC Advertisements
As described above, in PBB-EVPN, a single B-MAC address can aggregate
many C-MAC addresses. Given that B-MAC addresses are associated with
segments attached to a PE or to the PE itself, their locations are
fixed and thus not impacted what so ever by C-MAC mobility.
Therefore, C-MAC mobility does not affect B-MAC addresses (e.g., any
re-advertisements of them). 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. Aggregation via B-MAC addresses
in PBB-EVPN performs much better than EVPN.
To illustrate how this compares to EVPN, consider the following
example:
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If a PE running EVPN advertises reachability for N MAC addresses via
a particular segment, and then 50% of the MAC addresses in that
segment move to other segments (e.g. due to virtual machine
mobility), then N/2 additional MAC Advertisement routes need to be
sent for the MAC addresses that have moved. With PBB-EVPN, on the
other hand, the B-MAC addresses which are statically associated with
PE nodes, 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 in PBB-EVPN.
10.3. C-MAC Address Learning and Confinement
In PBB-EVPN, C-MAC address reachability information is built via
data-plane learning. As such, PE 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, PE nodes will not maintain any
record of them in control-plane routing table.
10.4. Seamless Interworking with 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.
+--------------+
| |
+---------+ | MPLS | +---------+
+----+ | | +----+ +----+ | | +----+
| CE |--| | | PE1| | PE2| | |--| CE |
+----+ | 802.1aq |---| | | |--| MPLS | +----+
+----+ | | +----+ +----+ | | +----+
| CE |--| | | Backbone | | |--| CE |
+----+ +---------+ +--------------+ +---------+ +----+
Figure 9: Interoperability with 802.1aq
If the MPLS backbone network employs EVPN, then the 802.1aq data-
plane encapsulation must be terminated on PE1 or the edge device
connecting to PE1. Either way, all the PE 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 PE1. If PBB-EVPN is also
extended over the MPLS access network on the right, then C-MAC
addresses would be transparent to PE2 as well.
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10.5. Per Site Policy Support
In PBB-EVPN, the per site policy can be supported via B-MAC addresses
via assigning a unique B-MAC address for every site/segment
(typically multi-homed but can also be single-homed). Given that the
B-MAC addresses are sent in BGP MAC/IP route advertisement, it is
possible to define per site (i.e. B-MAC) forwarding policies
including policies for E-TREE service.
10.6. No C-MAC Address Flushing for All-Active Multi-Homing
Just as in [RFC7432], with PBB-EVPN, it is possible to avoid C-MAC
address flushing upon topology change affecting an All-Active multi-
homed segment. To illustrate this, consider the example network of
Figure 1. Both PE1 and PE2 advertise the same B-MAC address (BM1) to
PE3. PE3 then learns the C-MAC addresses of the servers/hosts behind
CE1 via data-plane learning. If AC1 fails, then PE3 does not need to
flush any of the C-MAC addresses learnt and associated with BM1. This
is because PE1 will withdraw the MAC Advertisement routes associated
with BM1, thereby leading PE3 to have a single adjacency (to PE2) for
this B-MAC address. Therefore, the topology change is communicated to
PE3 and no C-MAC address flushing is required.
11. Acknowledgements
The authors would like to thank Jose Liste and Patrice Brissette for
their reviews and comments of this document. We would also like to
thank Giles Heron for several rounds of reviews and providing
valuable inputs to get this draft ready for IESG submission.
12. Security Considerations
All the security considerations in [RFC7432] apply directly to this
document because this document leverages [RFC7432] control plane and
their associated procedures - although not the complete set but
rather a subset.
This draft does not introduce any new security considerations beyond
that of [RFC7432] and [RFC4761] because advertisements and processing
of B-MAC addresses follow that of [RFC7432], and processing of C-MAC
addresses follow that of [RFC4761] - i.e, B-MAC addresses are learned
in control plane and C-MAC addresses are learned in data plane.
13. IANA Considerations
There is no additional IANA considerations for PBB-EVPN beyond what
is already described in [RFC7432].
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14. Normative References
[RFC7432] A. Sajassi, et al., "BGP MPLS Based Ethernet VPN", RFC
7432 , February 2015.
[PBB] Clauses 25 and 26 of "IEEE Standard for Local and
metropolitan area networks - Media Access Control (MAC)
Bridges and Virtual Bridged Local Area Networks", IEEE Std
802.1Q, 2013.
15. Informative References
[RFC7080] A. Sajassi, et al., "Virtual Private LAN Service (VPLS)
Interoperability with Provider Backbone Bridges", RFC
7080, December 2013.
[RFC7209] D. Thaler, et al., "Requirements for Ethernet VPN (EVPN)",
RFC 7209, May 2014.
[RFC4389] A. Sajassi, et al., "Neighbor Discovery Proxies (ND
Proxy)", RFC 4389, April 2006.
[RFC4761] K. Kompella, et al., "Virtual Private LAN Service (VPLS)
Using BGP for Auto-Discovery and Signaling", RFC 4761,
Jauary 2007.
[OVERLAY] A. Sajassi, et al., "A Network Virtualization Overlay
Solution using EVPN", draft-ietf-bess-evpn-overlay-01,
work in progress, February 2015.
[MMRP] Clause 10 of "IEEE Standard for Local and metropolitan
area networks - Media Access Control (MAC) Bridges and
Virtual Bridged Local Area Networks", IEEE Std 802.1Q,
2013.
16. 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
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Vancouver, BC V7X 1J1, Canada
Email: ssalam@cisco.com
Nabil Bitar
Verizon Communications
Email : nabil.n.bitar@verizon.com
Aldrin Isaac
Bloomberg
Email: aisaac71@bloomberg.net
Wim Henderickx
Alcatel-Lucent
Email: wim.henderickx@alcatel-lucent.be
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