7-4 - EVPN Model for Ethernet Services Delivery

Question 1

Describe EVPN.

Answer 1

• EVPN is a multivendor solution that IETF standardizes. It provides the following benefits:
• Integrated services: Integrated Layers 2 and 3 VPN services, L3VPN-like principles and operational experience for scalability and control, all-active multihoming, and PE load balancing with Equal-Cost Multipath (ECMP) enable load balancing of traffic to and from CEs that are multihomed to multiple PEs.
• Network efficiency: Eliminates the “flood and learn” mechanism and provides fast-reroute, resiliency, and faster reconvergence when the link to a dual-homed server fails. Also provides optimized broadcast, unknown-unicast, and multicast (BUM) traffic delivery.
• Service flexibility: Choice of MPLS or Virtual Extensible LAN (VxLAN) data plane encapsulation, support of existing and new services types (E-LAN, E-Line), peer PE autodiscovery, and redundancy group autosensing.

Question 2

T/F: Prior to the EVPN model implementation, previous technologies failed to meet the increasing demands for providing Ethernet services delivery.

Answer 2

True

Question 3

What are the components of the EVPN Technology Family?

Answer 3

• PBB-EVPN: This solution implements the E-LAN service. This feature also introduces advanced multihoming options, support for multipath, and user-defined BGP policy capabilities to Ethernet L2VPNs. PBB-EVPN uses BGP for MAC address distribution and learning over the packet-switched network (PSN).
• EVPN-VPWS: The EVPN-VPWS solution is an implementation of the E-Line service. This BGP control plane solution is for point-to-point services. It implements the signaling and encapsulation techniques for establishing an EVPN instance between a pair of PEs. It has the ability to forward traffic from one network to another without MAC lookup. The use of EVPN for VPWS eliminates the need for signaling single-segment and multisegment PWs for point-to-point Ethernet services. The EVPN-VPWS technology works in the IP and MPLS core. It supports BGP in the IP core and switches packets between the endpoints in the MPLS core.
• EVPN–E-Tree: This solution is an implementation of the E-Tree service that provides very efficient filtering. When traffic originates from a leaf and is destined to a leaf, it drops right away at the ingress PE. It also provides flexible support of leaf/root site connectivity where a root/leaf designation can be an attachment circuit or per MAC address.
• EVPN overlay: This solution is an implementation of the data center fabric (intra-DC Overlay) service.
• EVPN-IRB: This solution is an implementation of the Integrated Routing and Bridging (IRB) (Layer 2 and Layer 3 overlay) service.
• EVPN DCI: This solution is an implementation of the DCI (inter-DC) service.
• EVPN-IRB: This solution is an implementation of the IP-VPN (L3VPN) service.

Question 4

EVI (Ethernet VPN Instance)

Answer 4

• represents a VPN on a PE router
• similar to a VRF, but for EVPN
• has an RD and import/export route-targets

Question 5

Ethernet Segments

Answer 5

• represents a “site” connection.
• associated with access-facing interfaces
• ESI: identifier for an ethernet segment (unique 10-octet value)
• This becomes very important for multihoming

Question 6

Describe the role of BGP routes in EVPN.

Answer 6

• EVPN uses BGP as the control-plane protocol for announcing the necessary info
• Type 1 - Ethernet Auto Discovery (EAD) route
• Type 2 - MAC advertisement route
• Type 3 - Inclusive multicast route
• Type 4 - Ethernet segment route
• Type 5 - IP prefix advertisement route

Question 7

Describe the role of BGP route attributes in EVPN.

Answer 7

• BGP extended communities expands info that carries in the BGP routes and includes the following
  *ESI MPLS label
  *ES-import route-target
  *MAC mobility
  *Default gateway
  *Encapsulation

Question 8

EVPN multihoming mechanisms include the following:

Answer 8

• Multihomed Ethernet segment autodiscovery
• MAC mass-withdraw
• Split horizon
• Aliasing
• Designated forwarder
• ARP broadcast suppression
• Unknown unicast suppression

Question 9

Describe the traffic forwarding operation in EVPN.

Answer 9

• MAC address reachability - The EVPN Software MAC Learning feature enables the MAC addresses that one device learns to distribute to the other devices that connect to a network. BGP enables MAC address learning from the remote devices
• Unicast traffic forwarding - After the advertisements of MAC routes, unicast traffic can forward from a PE by imposing the appropriate multipoint-to-point VPN and PSN MPLS labels and forwarding the traffic to the destination PE.
• Handling of multidestination traffic - The PEs in a particular EVPN instance can use the following to send BUM traffic to other PEs
  *Ingress replication - A multicast flow can transmit only to PEs with receivers that are interested in the multicast flow.
  *Point-to-multipoint LSPs - You can create point-to-multipoint LSPs with Resource Reservation Protocol Traffic Engineering (RSVP-TE) or Multicast Label Distribution Protocol (MLDP) for inclusive P-multicast trees.
• Segment and PE failures - EVPN uses the following if a segment or PE router fails:
  *Segment failure - When a PE detects a failure of one of its attached Ethernet segments, it withdraws the per-ESI administrative distance route for the failed segment.
  *PE router failure - If a PE router fails, the other PEs detect the BGP session timeout and invalidate routes from the failed PE.
• MAC mobility procedure - A PE that is advertising a MAC address with its corresponding segment identifier for the first time, advertises it without a MAC mobility extended community and with a particular sequence number (higher sequence number denote freshness of the information). If the MAC moves to another segment (for example VM mobility), when it is discovered by the the new PE, it will begin advertising the same MAC with a different ESI, increasing the sequence number and with the MAC mobility extended community. A PE that is receiving a MAC/IP advertisement route for a MAC address with a different Ethernet segment identifier and a higher sequence number than what it had been previously advertised, withdraws its MAC/IP advertisement route and then install the new record.

Question 10

Which of the following statements is true?

A. L2VPN technologies were forced to evolve over time to meet scalability and operational needs.
B. In terms of IETF L2VPN technologies evolution, VPLS was an uncommon technology.
C. The EVI represents a physical segment on a PE router.
D. EVPN has no multihoming or suppression mechanisms.

Answer 10

A