rfc9786v1.txt		rfc9786.txt
	skipping to change at line 230 ¶		skipping to change at line 230 ¶
	b. The Ethernet Segment (ES) MUST be configured in Port-Active		b. The Ethernet Segment (ES) MUST be configured in Port-Active
	redundancy mode on peering PEs for the specified access		redundancy mode on peering PEs for the specified access
	interface.		interface.
	c. When ESI is configured on an L3 interface, the ES route (Route		c. When ESI is configured on an L3 interface, the ES route (Route
	Type-4) can be the only route exchanged by PEs in the redundancy		Type-4) can be the only route exchanged by PEs in the redundancy
	group.		group.
	d. PEs in the redundancy group leverage the DF election defined in		d. PEs in the redundancy group leverage the DF election defined in
	[RFC8584] to determine which PE keeps the port in active mode and		[RFC8584] to determine which PE keeps the port in active mode and
	which one(s) keep it in standby mode. Although the DF election		which PE(s) keeps it in standby mode. Although the DF election
	defined in [RFC8584] is per [ES, Ethernet Tag] granularity, the		defined in [RFC8584] is per [ES, Ethernet Tag] granularity, the
	DF election is performed per [ES] in Port-Active redundancy mode.		DF election is performed per [ES] in Port-Active redundancy mode.
	The details of this algorithm are described in Section 3.		The details of this algorithm are described in Section 3.
	e. The DF router MUST keep the corresponding access interface in an		e. The DF router MUST keep the corresponding access interface in an
	up and forwarding active state for that ES.		up and forwarding active state for that ES.
	f. Non-DF routers SHOULD implement a bidirectional blocking scheme		f. Non-DF routers SHOULD implement a bidirectional blocking scheme
	for all traffic comparable to the Single-Active blocking scheme		for all traffic comparable to the Single-Active redundancy mode
	described in [RFC7432], albeit across all VLANs.		described in [RFC7432], albeit across all VLANs.
	* Non-DF routers MAY bring and keep the peering access interface		* Non-DF routers MAY bring and keep the peering access interface
	attached to them in an operational down state.		attached to them in an operational down state.
	* If the interface is running the LACP protocol, the non-DF PE		* If the interface is running the LACP protocol, the non-DF PE
	MAY set the LACP state to Out of Sync (OOS) instead of setting		MAY set the LACP state to Out of Sync (OOS) instead of setting
	the interface to a down state. This approach allows for		the interface to a down state. This approach allows for
	better convergence during the transition from standby to		better convergence during the transition from standby to
	active mode.		active mode.
	skipping to change at line 274 ¶		skipping to change at line 274 ¶
	specified in Section 8.3 of [RFC7432] SHOULD be employed to prevent		specified in Section 8.3 of [RFC7432] SHOULD be employed to prevent
	transient echo packets when L2 circuits are involved.		transient echo packets when L2 circuits are involved.
	Various algorithms for DF election are detailed in Sections 3.2 to		Various algorithms for DF election are detailed in Sections 3.2 to
	3.5 for comprehensive understanding, although the choice of algorithm		3.5 for comprehensive understanding, although the choice of algorithm
	in this solution does not significantly impact complexity or		in this solution does not significantly impact complexity or
	performance compared to other redundancy modes.		performance compared to other redundancy modes.
	3.1. Capability Flag		3.1. Capability Flag
	[RFC8584] defines a DF Election Extended Community and a Bitmap (2		[RFC8584] defines a DF Election Extended Community and a bitmap (2
	octets) field to encode "DF Election Capabilities" to use with the DF		octets) field to encode "DF Election Capabilities" to use with the DF
	election algorithm in the DF algorithm field:		election algorithm in the DF algorithm field:
	Bit 0: D bit or 'Don't Preempt' bit, as described in [RFC9785].		Bit 0: D bit or 'Don't Preempt' bit, as described in [RFC9785].
	Bit 1: AC-Influenced DF (AC-DF) election, as described in		Bit 1: AC-Influenced DF (AC-DF) election, as described in
	[RFC8584].		[RFC8584].
			Bit 3: Time Synchronization, as described in [RFC9722].
	1 1 1 1 1 1		1 1 1 1 1 1
	0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	|D|A| |P| |		|D|A| |T| |P| |
	+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	Figure 2: Amended DF Election Capabilities in the DF Election		Figure 2: Amended DF Election Capabilities in the DF Election
	Extended Community		Extended Community
	This document defines the following value and extends the DF Election		This document defines the following value and extends the DF Election
	Capabilities bitmap field:		Capabilities bitmap field:
	Bit 5: Port Mode Designated Forwarder Election. This bit		Bit 5: Port Mode Designated Forwarder Election. This bit
	determines that the DF election algorithm SHOULD be		determines that the DF election algorithm SHOULD be
	skipping to change at line 329 ¶		skipping to change at line 331 ¶
	defined in [RFC8584], and it MAY be used and signaled. For Port-		defined in [RFC8584], and it MAY be used and signaled. For Port-
	Active, this is modified to operate at the granularity of <ES> rather		Active, this is modified to operate at the granularity of <ES> rather
	than per <ES, VLAN>.		than per <ES, VLAN>.
	Section 3.2 of [RFC8584] describes computing a 32-bit Cyclic		Section 3.2 of [RFC8584] describes computing a 32-bit Cyclic
	Redundancy Check (CRC) over the concatenation of Ethernet Tag (V) and		Redundancy Check (CRC) over the concatenation of Ethernet Tag (V) and
	ESI (Es). For Port-Active redundancy mode, the Ethernet Tag is		ESI (Es). For Port-Active redundancy mode, the Ethernet Tag is
	omitted from the CRC computation and all references to (V, Es) are		omitted from the CRC computation and all references to (V, Es) are
	replaced by (Es).		replaced by (Es).
	The algorithm to determine the DF Elected and Backup-DF Elected (BDF)		The algorithm used to determine the DF and Backup Designated
	at Section 3.2 of [RFC8584] is repeated and summarized below using		Forwarder (BDF) per Section 3.2 of [RFC8584] is repeated and
	only (Es) in the computation:		summarized below using only (Es) in the computation:
	1. DF(Es) = Si| Weight(Es, Si) >= Weight(Es, Sj), for all j. In the		1. DF(Es) = Si| Weight(Es, Si) >= Weight(Es, Sj), for all j. In the
	case of a tie, choose the PE whose IP address is numerically the		case of a tie, choose the PE whose IP address is numerically the
	least. Note that 0 <= i,j < number of PEs in the redundancy		least. Note that 0 <= i,j < number of PEs in the redundancy
	group.		group.
	2. BDF(Es) = Sk| Weight(Es, Si) >= Weight(Es, Sk), and Weight(Es,		2. BDF(Es) = Sk| Weight(Es, Si) >= Weight(Es, Sk), and Weight(Es,
	Sk) >= Weight(Es, Sj). In the case of a tie, choose the PE whose		Sk) >= Weight(Es, Sj). In the case of a tie, choose the PE whose
	IP address is numerically the least.		IP address is numerically the least.
	skipping to change at line 431 ¶		skipping to change at line 433 ¶
	Implementations that comply with [RFC7432] or [RFC8214] only (i.e.,		Implementations that comply with [RFC7432] or [RFC8214] only (i.e.,
	implementations that predate this specification) and that receive an		implementations that predate this specification) and that receive an
	L2-Attr Extended Community in Ethernet A-D per ES routes will ignore		L2-Attr Extended Community in Ethernet A-D per ES routes will ignore
	it and continue to use the default path resolution algorithms of the		it and continue to use the default path resolution algorithms of the
	two specifications above:		two specifications above:
	* The L2-Attr Extended Community in Ethernet A-D per ES route is		* The L2-Attr Extended Community in Ethernet A-D per ES route is
	ignored.		ignored.
	* The remote ESI label extended community [RFC7432] signals Single-		* The remote ESI Label Extended Community [RFC7432] signals the
	Active (Section 3).		Single-Active redundancy mode (Section 3).
	* The remote Media Access Control (MAC) and/or Ethernet A-D per EVI		* The remote Media Access Control (MAC) and/or Ethernet A-D per EVI
	routes are unchanged; the P and B bits in the L2-Attr Extended		routes are unchanged; the P and B bits in the L2-Attr Extended
	Community in Ethernet A-D per EVI routes are used.		Community in Ethernet A-D per EVI routes are used.
	5. Applicability		5. Applicability
	A prevalent deployment scenario involves providing L2 or L3 services		A prevalent deployment scenario involves providing L2 or L3 services
	on PE devices that offer multi-homing capabilities. The services may		on PE devices that offer multi-homing capabilities. The services may
	include any L2 EVPN solutions such as EVPN Virtual Private Wire		include any L2 EVPN solutions such as EVPN Virtual Private Wire
	skipping to change at line 486 ¶		skipping to change at line 488 ¶
	applicable to this document.		applicable to this document.
	Introducing a new capability necessitates unanimity among PEs.		Introducing a new capability necessitates unanimity among PEs.
	Without consensus on the new DF election procedures and Port Mode,		Without consensus on the new DF election procedures and Port Mode,
	the DF election algorithm defaults to the procedures outlined in		the DF election algorithm defaults to the procedures outlined in
	[RFC8584] and [RFC7432].This fallback behavior could be exploited by		[RFC8584] and [RFC7432].This fallback behavior could be exploited by
	an attacker who modifies the configuration of one PE within the ES.		an attacker who modifies the configuration of one PE within the ES.
	Such manipulation could force all PEs in the ES to revert to the		Such manipulation could force all PEs in the ES to revert to the
	default DF election algorithm and capabilities. In this scenario,		default DF election algorithm and capabilities. In this scenario,
	the PEs may be subject to unfair load balancing, service disruption,		the PEs may be subject to unfair load balancing, service disruption,
	and potential issues such as black-holing or duplicate traffic, as		and potential issues such as traffic loss or duplicate traffic, as
	mentioned in the security sections of those documents.		mentioned in the security sections of those documents.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[IEEE_802.1AX_2014]		[IEEE_802.1AX_2014]
	IEEE, "IEEE Standard for Local and metropolitan area		IEEE, "IEEE Standard for Local and metropolitan area
	networks -- Link Aggregation", IEEE 802-1ax-2014,		networks -- Link Aggregation", IEEE 802-1ax-2014,
	DOI 10.1109/IEEESTD.2014.7055197, 5 March 2015,		DOI 10.1109/IEEESTD.2014.7055197, 5 March 2015,
	skipping to change at line 524 ¶		skipping to change at line 526 ¶
	Rabadan, "Virtual Private Wire Service Support in Ethernet		Rabadan, "Virtual Private Wire Service Support in Ethernet
	VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,		VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
	<https://www.rfc-editor.org/info/rfc8214>.		<https://www.rfc-editor.org/info/rfc8214>.
	[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,		[RFC8584] Rabadan, J., Ed., Mohanty, S., Ed., Sajassi, A., Drake,
	J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet		J., Nagaraj, K., and S. Sathappan, "Framework for Ethernet
	VPN Designated Forwarder Election Extensibility",		VPN Designated Forwarder Election Extensibility",
	RFC 8584, DOI 10.17487/RFC8584, April 2019,		RFC 8584, DOI 10.17487/RFC8584, April 2019,
	<https://www.rfc-editor.org/info/rfc8584>.		<https://www.rfc-editor.org/info/rfc8584>.
			[RFC9722] Brissette, P., Sajassi, A., Burdet, LA., Ed., Drake, J.,
			and J. Rabadan, "Fast Recovery for EVPN Designated
			Forwarder Election", RFC RFC9722, May 2025,
			<https://www.rfc-editor.org/info/rfc9722>.
	[RFC9785] Rabadan, J., Ed., Sathappan, S., Lin, W., Drake, J., and		[RFC9785] Rabadan, J., Ed., Sathappan, S., Lin, W., Drake, J., and
	A. Sajassi, "Preference-Based EVPN Designated Forwarder		A. Sajassi, "Preference-Based EVPN Designated Forwarder
	(DF) Election", RFC RFC9785, DOI 10.17487/RFC9785, May		(DF) Election", RFC RFC9785, DOI 10.17487/RFC9785, May
	2025, <https://www.rfc-editor.org/info/rfc9785>.		2025, <https://www.rfc-editor.org/info/rfc9785>.
	8.2. Informative References		8.2. Informative References
	[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private		[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
	Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February		Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
	2006, <https://www.rfc-editor.org/info/rfc4364>.		2006, <https://www.rfc-editor.org/info/rfc4364>.
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