Allowing Traffic in EVPN Tree Service

D.

E VPN (Ethernet VPN) is a technology used in Service Provider networks to provide virtual Ethernet segments across an IP/MPLS infrastructure. E VPN is an enhancement to Virtual Private LAN Service (VPLS) and provides better scalability, flexibility, and convergence.

In E VPN, traffic is carried over a BGP (Border Gateway Protocol) MPLS-based network. The BGP E VPN address family is used to exchange MAC (Media Access Control) and IP (Internet Protocol) reachability information between the Provider Edge (PE) devices. Each E VPN instance is identified by a unique E VPN instance ID (EVI) and is associated with a VLAN or VXLAN (Virtual Extensible LAN) segment.

An E VPN Tree Service is a type of E VPN service that provides Layer 2 multicast forwarding between multiple PE devices. In an E VPN Tree Service, a root node is responsible for forwarding multicast traffic to all the leaf nodes. The leaf nodes receive the multicast traffic and forward it to the appropriate VLAN or VXLAN segment.

Now, coming to the question, the engineer is investigating an E VPN traffic flow issue and wants to know which type of traffic should be allowed in an E VPN Tree Service to fix this issue.

Option A: Known unicast from a leaf to another leaf Known unicast traffic is the traffic that is destined for a specific MAC address and is known to the network. In E VPN, known unicast traffic is forwarded directly from the source leaf to the destination leaf, without involving the root node. All the PEs in the E VPN instance maintain the MAC-to-PE mapping and use BGP E VPN to advertise the MAC reachability information. However, allowing known unicast traffic from a leaf to another leaf would not help in fixing the traffic flow issue in an E VPN Tree Service, as it does not involve multicast traffic.

Option B: Unknown unicast from a leaf to another leaf Unknown unicast traffic is the traffic that is destined for a specific MAC address but is not known to the network. In E VPN, unknown unicast traffic is flooded to all the PE devices in the same E VPN instance. Each PE device learns the MAC address and the corresponding attachment circuit from which the traffic was received. Allowing unknown unicast traffic from a leaf to another leaf would not help in fixing the traffic flow issue in an E VPN Tree Service, as it does not involve multicast traffic.

Option C: Multicast from a leaf to another leaf Multicast traffic is the traffic that is destined for a group of devices and is sent to all the devices that belong to that group. In E VPN, multicast traffic is forwarded by the root node to all the leaf nodes in the E VPN Tree Service. The leaf nodes then forward the multicast traffic to the appropriate VLAN or VXLAN segment. Allowing multicast traffic from a leaf to another leaf would help in fixing the traffic flow issue in an E VPN Tree Service, as it involves multicast traffic.

Option D: Known unicast from a root to another root Known unicast traffic between root nodes is not relevant to fixing the traffic flow issue in an E VPN Tree Service, as it does not involve multicast traffic.

Therefore, the correct answer is option C: Multicast from a leaf to another leaf.