Flush Mechanism for Customer MAC Addresses Based on Service Instance Identifier (I-SID) in Provider Backbone Bridging EVPN (PBB-EVPN)
Extracted elements (23)
Existing C-MAC flush in RFC 7623 operates at B-MAC granularity (B-MAC/0 routes) and, when reused for null-ESI scenarios, causes unnecessary flushing of all I-SIDs associated with a B-MAC rather than only the affected I-SID. This document introduces I-SID-encoded Ethernet Tag in MAC/IP Advertisement routes to achieve per-I-SID flush granularity.
The solution reuses existing BGP attributes (MAC Mobility extended community and EVPN MAC/IP Advertisement route) rather than defining new ones, encoding the I-SID in the Ethernet Tag field. This ensures RRs accept and reflect B-MAC/I-SID routes without modification, providing reliable flush propagation in networks with Route Reflectors.
Non-supporting PEs (those not implementing this specification) will ignore received B-MAC/I-SID routes because the routes use no new BGP attributes or values. These PEs continue to follow RFC 7623 C-MAC flush procedures using B-MAC/0 routes, ensuring backward compatibility.
The B-MAC/I-SID route is accepted and reflected by any Route Reflector compliant with RFC 7432 because it introduces no new BGP attributes; only PEs supporting this specification will act on the received B-MAC/I-SID update.
A PE receiving RFC 7623 C-MAC flush notification messages (B-MAC/0 routes) MUST observe the behavior specified in RFC 7623; those procedures remain valid and unmodified.
A received B-MAC/I-SID route (with a non-zero I-SID) MUST NOT add or remove any B-MAC to or from the MAC-VRF; its sole function is to trigger C-MAC flush.
A received B-MAC/I-SID withdraw (with a non-zero I-SID) MUST flush all C-MACs associated with that B-MAC and I-SID.
An AC going operationally down MUST generate a B-MAC/I-SID route with a higher Sequence Number. If the failure causes the entire local I-SID to go operationally down, the PE MUST withdraw the B-MAC/I-SID route for that I-SID.
An AC going operationally up SHOULD NOT generate any B-MAC/I-SID update, unless it activates its corresponding I-SID, in which case the PE advertises the B-MAC/I-SID route.
An AC receiving a G.8032 flush notification or a flush message from any other access network protocol MAY propagate it to remote PEs by generating a B-MAC/I-SID route update with a higher Sequence Number.
An update of a previously received B-MAC/I-SID route with an incremented Sequence Number MUST flush all C-MACs associated with that I-SID and B-MAC. C-MACs associated with the same I-SID but a different B-MAC MUST NOT be flushed.
Enabling or disabling I-SID-based C-MAC flush SHOULD be an administrative choice and MAY be configured per I-SID (I-Component), rather than being enabled globally for all I-SIDs.
In case of failure on the egress PE, the solution MUST provide a C-MAC flush notification at B-MAC and I-SID granularity level, limiting unnecessary flushing to only the affected I-SID.
Receiving PEs MUST use B-MAC/I-SID routes only for C-MAC flush procedures and MUST NOT use them to add or withdraw any B-MAC entry in the MAC-VRFs; only B-MAC/0 routes may add or withdraw B-MACs.
The I-SID-based C-MAC flush extension MUST work with Single-Active non-null ESs and virtual ESs, irrespective of the PE B-MAC address assignment model (dedicated per-ES B-MAC or shared B-MAC).
The solution MUST coexist in RFC 7623 networks where some PEs do not support this specification; non-supporting PEs ignore B-MAC/I-SID routes but still follow RFC 7623 C-MAC flush procedures.
The solution MUST prevent packet-loss scenarios in case of failures on null ES Attachment Circuits (ESI = zero) where the access device or access network is responsible for redundancy.
The solution MUST provide reliable C-MAC flush notification in PBB-EVPN networks using Route Reflectors, ensuring MAC flushing reaches all affected I-SIDs even when BGP flush notification messages are aggregated at the RR.
The B-MAC/0 route is an EVPN MAC/IP Advertisement route with a B-MAC in the MAC address field and Ethernet Tag ID set to zero, used as in RFC 7623 to add or withdraw B-MAC entries in the MAC-VRFs. It is distinct from the B-MAC/I-SID route introduced by this document.
The B-MAC/I-SID route is an EVPN MAC/IP Advertisement route that encodes a B-MAC address in the MAC address field and an I-SID value in the Ethernet Tag field (instead of zero). It is used exclusively as a C-MAC flush notification for C-MACs associated with the specified B-MAC and I-SID.
Security considerations from RFC 7623 apply. Additionally, the extra B-MAC/I-SID routes generated by this feature may consume additional memory and processing resources on receiving PEs, including non-supporting ones. It is RECOMMENDED to activate the feature only when necessary (when multihomed networks or devices are attached), and not by default on any PBB-EVPN PE.
I-SID-based C-MAC flush activation transitions a PE between inactive (not generating or processing B-MAC/I-SID routes) and active states on a per-I-SID basis. Activation is triggered administratively; deactivation removes the capability per I-SID. When active, the PE generates flush notifications on AC-down events and processes incoming B-MAC/I-SID routes.
The C-MAC flush notification reuses the MAC Mobility extended community (Type=0x06, Sub-Type=0x03) with an incremented Sequence Number, combined with an EVPN MAC/IP Advertisement route where ESI=0, Ethernet Tag ID = I-SID, MAC Address Length = 48 bits (B-MAC), and IP Address Length = 0.