In an EVPN multi-homing all-active mode, a Customer Edge (CE) device is connected to multiple Provider Edge (PE) routers, and all the links are active and can be used for forwarding traffic. This setup provides both load balancing and redundancy. All PEs attached to the same Ethernet Segment (ES) advertise the same Ethernet Segment Identifier (ESI) and can forward traffic to and from the CE for a given service. This is the fundamental operational principle of all-active multi-homing.

A. In single-active mode, the CE is typically connected via individual links, not a LAG. A multi-chassis LAG (MC-LAG) is characteristic of the all-active mode.

B. In single-active mode, only one PE (the Designated Forwarder) is active for a service. Therefore, the CE forwards and receives traffic through that single active PE only.

D. The Nokia 7750 SR supports a CE being multi-homed to more than two PEs. The specific limit is up to four PEs for all-active mode and up to eight PEs for single-active mode.

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 2 Services and EVPN Guide, SR OS Release 22.10.R1.

Section: EVPN for VPLS and Epipe Services > EVPN Multi-homing

Content: This section explicitly describes the two multi-homing modes. For all-active, it states: "In all-active mode, the CE is connected to the PEs through a LAG and all the links in the LAG can be used to send and receive traffic." This directly supports answer C. For single-active, it states: "In single-active mode... Only one of the links between the CE and the PEs is active at a time." This refutes options A and B. The guide also specifies the supported scale: "A CE can be multi-homed to up to four PEs in all-active mode, or up to eight PEs in single-active mode," which refutes option D.

2. IETF RFC 7432: BGP MPLS-Based Ethernet VPN.

Section: 8.3.1. All-Active Redundancy Mode

Content: "In this mode of operation, a CE may be connected to two or more PEs via a set of Ethernet links that constitute a Link Aggregation Group (LAG). From the CE's perspective, it is connected to a single device. In this mode, all PEs attached to the Ethernet segment are allowed to forward traffic to/from that Ethernet segment." This standard definition validates answer C.

3. IETF RFC 7432: BGP MPLS-Based Ethernet VPN.

Section: 8.3.2. Single-Active Redundancy Mode

Content: "In this mode of operation, a CE is connected to two or more PEs, but only one of these PEs is allowed to forward traffic to/from the CE for a given EVI." This standard definition confirms that the behavior described in option B is incorrect for single-active mode.