Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9541.¶

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Table of Contents

1. Introduction

[RFC7623] defines how Provider Backbone Bridging (PBB) can be combined with Ethernet Virtual Private Networks (EVPNs) to deploy E-LAN services in very large MPLS networks. [RFC7623] also describes how Single-Active multihoming and per-I-SID load-balancing can be provided to access devices and aggregation networks. When Access Ethernet and/or MPLS networks exist, [EVPN-VIRTUAL-ES] describes how virtual Ethernet Segments (ESs) can be associated with a group of Ethernet Virtual Circuits (EVCs) or even pseudowires (PWs). In order to speed up the network convergence in case of failures on Single-Active multihomed ESs, [RFC7623] defines a Customer MAC flush mechanism that works for different ES B-MAC address allocation models.¶

In some cases, the administrative entities that manage the access devices or aggregation networks do not demand multihomed ESs from the PBB-EVPN provider, but simply demand multiple single-homed ESs. Single-homed ESs use null ESIs, whereas multihomed ESs use non-null ESIs. If using single-homed ESs, the PBB-EVPN network is no longer aware of the redundancy offered by the access administrative entity. Figure 1 shows an example where the PBB-EVPN network provides four different Attachment Circuits (ACs) for I-SID1, with those ACs not being part of any ES or virtual ES. (Therefore, they are referred to as null virtual Ethernet Segments.)¶

<----G.8032----><--PBB-EVPN Network-----><----MPLS---->
     Access          MPLS                Access
      Ring                               Network
I-SID1      ESI +------+         +------+
+----+      null| PE1  |---------| PE3  |
|CE1 |----------|B-MAC1|         |B-MAC3| ESI null
+----+    active|      |         |      |----+ PW
  |             +------+         +------+     \active
  |               |                 |          \  +----+
  |               |                 |           ==|CE3 |I-SID1
  |               |                 |          /  +----+
  |standby  ESI +------+         +------+     / PW
+----+      null| PE2  |         | PE4  |----+ standby
|CE2 |----------|B-MAC2|         |B-MAC4| ESI null
+----+    active|      |---------|      |
I-SID1          +------+         +------+

In the example in Figure 1, CE1, CE2, and CE3 are attached to the same service, identified by I-SID1, in the PBB-EVPN PEs. CE1 and CE2 are connected to the PEs via "Ethernet ring protection switching" as specified in [G.8032], and their ACs to PE1 and PE2 are represented by a port and VLAN identifier. CE3 is dual-homed to PE3 and PE4 through an active/standby PW, and its AC to the PEs is represented by a PW. Each of the four PEs uses a dedicated Backbone MAC address as a source MAC address (B-MAC1, B-MAC2, B-MAC3, and B-MAC4, respectively) when encapsulating customer frames in PBB packets and forwarding those PBB packets to the remote PEs as per [RFC7623]. There are no multihomed ESs defined in the PBB-EVPN network of the example; that is why the four ACs in Figure 1 show the text "ESI null", which means the Ethernet Segment Identifier on those ACs is zero. Since there are no multihomed ESs defined, the PEs keep their ACs active as long as the physical connectivity is established and the CEs are responsible for managing the redundancy, avoiding loops, and providing per-I-SID load-balancing to the PBB-EVPN network. Examples of CEs managing their own redundancy are described in [G.8032], or [RFC4762] for active/standby PWs.¶

For instance, in normal conditions, CE2 will block its link to CE1 and CE3 will block its forwarding path to PE4. In this situation, a failure in one of the redundant ACs will trigger the CEs to start using their redundant paths; however, those failures will not trigger any C-MAC flush procedures in the PEs that implement [RFC7623], since the PEs are not using the PBB-EVPN multihoming procedures. For example:¶

• If the active PW from CE3 (to PE3) fails and the failure is due to the entire PE3 node failing, then the procedures in [RFC7623] guarantee that all the remote PEs flush all the C-MACs associated with B-MAC3 (the B-MAC of PE3). In this case, CE3 detects the fault due to the PW going operationally down.¶

• However, if the active PW from CE3 (to PE3) fails (but PE3 is still operationally up), following the procedures in [RFC7623], neither PE3 nor PE4 issue a C-MAC flush message. Therefore, the remote PEs will continue pointing at PE3's B-MAC to reach CE3's C-MACs, until the C-MACs age out in the I-SID1 forwarding tables. In this case, PE3 may use any of the existing PW notifications so that CE3 switches the active PW to PE4.¶

• The same issue is exposed when the active PW from CE3 switches over from PE3 to PE4 due to a manual operation on CE3; that is, neither PE3 nor PE4 trigger any C-MAC flush notification and the remote PEs continue sending the traffic to PE3 until the C-MACs age out.¶

[RFC7623] provides a C-MAC flush solution based on a shared B-MAC update along with the MAC Mobility extended community where the sequence number is incremented. However, the procedure is only used along with multihomed ESs. Even if that procedure could be used for null ESs, as in the example of Figure 1, the Customer MAC flush procedure in [RFC7623] would result in unnecessary flushing of unaffected I-SIDs on the remote PEs, and subsequent flooding of unknown unicast traffic in the network. For instance, in the case that CE3 switches its active PW over to PE4, a potential solution reusing the existing C-MAC flush notifications in [RFC7623] is for PE3 to issue an update for the MAC/IP Advertisement route of B-MAC3 with a higher sequence number. However, this update would cause unnecessary Customer MAC flushing for all the I-SIDs attached to PE3 (supposing multiple I-SIDs in PE3) rather than for only I-SID1.¶

This document describes an extension of the Customer MAC flush procedures in [RFC7623], so that in the failure example above, PE3 can trigger a Customer MAC flush notification that makes PE1, PE2, and PE4 flush all the Customer MACs associated with PE3's B-MAC3 and (only) I-SID1. In order to do so, this specification introduces the encoding of the I-SID in the MAC/IP Advertisement routes advertised for the B-MACs. The C-MAC flush procedure explained in this document is referred to as "PBB-EVPN I-SID-based C-MAC flush" and can be used in PBB-EVPN networks with null or non-null (virtual) ESs.¶

This specification assumes that the reader is familiar with the procedures in [RFC7623].¶

2. Solution Requirements

The following requirements are followed by the C-MAC flush solution described in this document:¶

1. The solution MUST prevent packet-loss scenarios in case of failures on null ES ACs (Attachment Circuits not associated with an ES; that is, their corresponding ESI is zero) when the access device or access network is responsible for the redundancy.¶

2. This extension described in this document MUST work with Single-Active non-null ESs and virtual ESs, irrespective of the PE B-MAC address assignment (dedicated per-ES B-MAC or shared B-MAC, as in [RFC7623]).¶

3. In case of failure on the egress PE, the solution MUST provide a C-MAC flush notification at the B-MAC and I-SID granularity level.¶

4. The solution MUST provide a reliable C-MAC flush notification in PBB-EVPN networks that use Route Reflectors (RRs). MAC flushing needs to be provided to all affected I-SIDs in spite of the BGP flush notification messages being aggregated at the RR.¶

5. The solution MUST coexist in [RFC7623] networks where there are PEs that do not support this specification.¶

6. The solution SHOULD be enabled or disabled by an administrative option on a per-PE and per-I-SID basis (as opposed to always being enabled for all the I-SIDs).¶

3. EVPN BGP Encoding for I-SID-Based C-MAC Flush

The solution does not use any new BGP attributes but reuses the MAC Mobility extended community as an indication of C-MAC flush (as in [RFC7623]) and encodes the I-SID in the Ethernet Tag field of the EVPN MAC/IP advertisement route. As a reference, Figure 2 shows the MAC Mobility extended community and the EVPN MAC/IP advertisement route that are used as specified in [RFC7432] and used in this document as a C-MAC flush notification message.¶

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06     | Sub-Type=0x03 |   Flags       |   Reserved=0  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Sequence Number                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            +---------------------------------------+
            |  Route Distinguisher                  |
            +---------------------------------------+
            |  ESI = 0                              |
            +---------------------------------------+
            |  Ethernet Tag ID = I-SID              |
            +---------------------------------------+
            |  MAC Address Length = 48              |
            +---------------------------------------+
            |  B-MAC Address                        |
            +---------------------------------------+
            |  IP Address Length = 0                |
            +---------------------------------------+
            |  MPLS Label1                          |
            +---------------------------------------+

Where:¶

• The route's route distinguisher and route targets are the ones corresponding to its EVI. Alternatively to the EVI's Route Target (RT), the route MAY be tagged with an RT auto-derived from the Ethernet Tag (I-SID) instead. [RFC7623] describes how the EVPN MAC/IP Advertisement routes can be advertised along with the EVI RT or an RT that is derived from the I-SID.¶

• The Ethernet Tag encodes the I-SID. This indicates to the PE that it must flush the C-MACs for that encoded I-SID, upon reception of the route.¶

• The MAC address field encodes the B-MAC address. This indicates to the PE that it must flush the C-MACs associated with that encoded B-MAC, upon reception of the route.¶

• The MAC Mobility extended community is used as in [RFC7623], where an increment in the sequence number between two updates for the same B-MAC/I-SID will be interpreted as a C-MAC flush notification for the corresponding B-MAC and I-SID.¶

All the other fields are set and used as defined in [RFC7623]. This document will refer to this route as the "B-MAC/I-SID route", as opposed to the EVPN MAC/IP Advertisement route used in [RFC7623] that contains a specific B-MAC and the Ethernet Tag ID set to zero. This document uses the term "B-MAC/0 route" to represent a B-MAC route advertised with an Ethernet Tag ID = 0.¶

Note that this B-MAC/I-SID route will be accepted and reflected by any RR as specified in [RFC7432], since no new attributes or values are used. A PE receiving the route will process the received B-MAC/I-SID update only in the case of supporting the procedures described in this document.¶

4. Solution Description

Figure 1 will be used in the description of the solution. CE1, CE2, and CE3 are connected to ACs associated with I-SID1, where no (multihomed) ESs have been enabled, and the ACs and PWs are in active or standby state as per Figure 1.¶

Enabling or disabling I-SID-based C-MAC flush SHOULD be an administrative choice on the system that MAY be configured per I-SID (I-Component, Service Instance Component), as opposed to being configured for all I-SIDs. When enabled on a PE:¶

1. The PE will be able to generate B-MAC/I-SID routes as C-MAC Flush notifications for the remote PEs.¶

2. The PE will be able to process B-MAC/I-SID routes received from remote PEs.¶

The PE MUST follow the procedures in [RFC7623] for C-MAC flush. This specification provides some additional procedures when I-SID-based C-MAC flush is enabled.¶

This C-MAC flush specification is described in three sets of procedures:¶

• I-SID-based C-MAC flush activation¶

• C-MAC flush notification generation upon AC failures¶

• C-MAC flush process upon receiving a C-MAC flush notification¶

5. Conclusions

The I-SID-based C-MAC flush solution described in this document has the following benefits:¶

1. The solution solves packet-loss scenarios in case of failures on null ES ACs, since the C-MAC flush procedures are independent of the ES definition.¶

2. This extension can also be used with Single-Active non-null ESs and virtual ESs, irrespective of the PE B-MAC address assignment (dedicated per-ES B-MAC or shared B-MAC).¶

3. It provides a C-MAC flush notification at B-MAC and I-SID granularity level, therefore flushing a minimum number of C-MACs and reducing the amount of unknown unicast flooding in the network.¶

4. It provides a reliable C-MAC flush notification in PBB-EVPN networks that use RRs. RRs will propagate the C-MAC flush notifications for all the affected I-SIDs, irrespective of the order in which the notifications make it to the RR.¶

5. The solution can coexist in a network with systems supporting or not supporting this specification. Non-supporting systems ignore the B-MAC/I-SID routes; however, they still follow the C-MAC flush procedures in [RFC7623].¶

6. Security Considerations

Security considerations described in [RFC7623] apply to this document.¶

In addition, this document suggests additional procedures that can be activated on a per I-SID basis and generate additional EVPN MAC/IP Advertisement routes in the network. The format of these additional EVPN MAC/IP Advertisement routes is backwards compatible with the procedures in [RFC7623] and should not create any issues for receiving PEs that do not follow this specification. However, the additional routes may consume extra memory and processing resources on the receiving PEs. Because of that, it is RECOMMENDED to activate this feature only when necessary (when multihomed networks or devices are attached to the PBB-EVPN PEs), and not by default in any PBB-EVPN PE.¶

7. IANA Considerations

This document has no IANA actions.¶

Acknowledgments

The authors want to thank Vinod Prabhu, Sriram Venkateswaran, Laxmi Padakanti, and Ranganathan Boovaraghavan for their review and contributions.¶

Authors' Addresses