EVPN and L2 Access Protocols: Single-Flow-Active load-balancing mode draft-brissette-bess-evpn-l2gw-proto

Requirements Support L2 Access Protocols into EVPN core (incl. EVPN-IRB). (M)STP 802.1d, G.8032, MPLS-TP, MST-AG, REP-AG, etc. L2 gateways largely unaware of the access network topology but Access network is running an L2 protocol breaking loops Access network is segmented by design Solution MUST support: Optimal forwarding at L2 and L3 Fast-convergence Scalability Anycast IRB support

Challenges with existing load-balancing modes PE1 PE2 Sw-A Sw-D Sw-C Sw-B Possible location of blocked port Access networks MPLS / EVPN PE3 BVI /24 BLK* FWD L2 BUM: isolated switches DF Election ECMP Untagged AC: EVPN-VPWS All-Active creates L2 and L3 aliasing resulting in remote ECMP towards “wrong” PE L2 BUM isolated switches TCN propagation blocked by ESI split-horizon label filtering SHG Filter

Challenges with existing load-balancing modes PE3 Single-Active Isolates network segments TCN propagation blocked by port state or ESI split-horizon label filtering MPLS / EVPN Untagged AC: EVPN-VPWS PE1 PE2 BVI /24 BVI /24 BLK FWD DF Election Sw-A Sw-B Isolated switches Possible location of blocked port Access networks Sw-D Sw-C

Untagged AC: EVPN-VPWS Single-Flow-Active PE3 Active / Backup MPLS / EVPN Same ESI between peering PEs: Ethernet-segment procedures still apply ESI-Label BGP extcomm extension to signal [2:0]- 000 = all-active, 001 = single-active, 010 = single-flow-active, other = unused [7:3]- Reserved Peering PE in SFA mode, MUST: not perform ESI Split-Horizon filtering enable MAC-Mobility within same ESI Remote PE for remote ESI in SFA mode: MUST disable aliasing (at Layer-2 and Layer-3) SHOULD pre-program backup per MAC entry Untagged AC: EVPN-VPWS PE1 PE2 BVI /24 BVI /24 FWD FWD No ESI Split-horizon Common ESI means Ethernet-segment procedures other than DF still apply: such as MAC+IP sync, Mass-Withdraw, etc. DF / Port state dictated by Access Protocol. PEs are behaving in Gateway mode, both PEs always Forwarding The ESI-Label BGP extcomm is extended to signal new single-flow multi-homing mode, in the flags field contiguous to A/A and S/A flags Redundancy mode field in flags. Remote PE for remote ESI in S-F/A mode will receive the new mode in an ES/EAD update SHOULD pre-program backup per MAC entry, this is same as for S/A mode Sw-A Sw-B Possible location of blocked port Access protocol STP, ERP, ... Sw-D Sw-C

Single-Flow-Active: TCN PE3 Active / Backup MPLS / EVPN Peering PEs, upon receiving TCN from access Perform local MAC flush MAY result in MAC RT-2 withdraws TCN propagation via dedicated PW EVPN-VPWS well-suited for this Relay TCN between peering PEs and also forward back into access Peering access PEs MAY map TCN into EVI/EAD “Flush” extcomm with new Sequence ID Untagged AC: EVPN-VPWS PE1 PE2 BVI /24 BVI /24 FWD FWD No ESI Split-horizon Peering PEs, upon receiving TCN from Access Perform local MAC flush (MAY result in MAC RT-2 withdraws) TCN Propagation via dedicated PW (i.e. EVPN-VPWS) on Untagged AC Relay TCN between peering PEs and also forward back into Access Remote PEs are unaware of TCN: Peering Access PEs must map TCN into EVI/EAD “Flush” extcomm with new Sequence ID The MAC may be re-learnt and advertised by the same PE or by another, in the same ESI MAC-Move procedures MUST be used within same ESI in this case to refresh the MAC in BGP. Sw-A Sw-B Possible location of blocked port Access protocol STP, ERP, ... Sw-D Sw-C