EVPN Type 5 (IP Prefix Route) Explained

EVPN Type 5 route that is proposed in ‘IP Prefix Advertisement in EVPN’ draft is a mechanism to carry IPv4 and IPv6 advertisements in EVPN-only networks. While EVPN Type 2 routes allow to carry both MAC addresses and IP addresses, tight coupling of specific IP addresses with IP Prefixes might not be desirable. Section 2.2 of the draft discusses different scenarios where such coupling is nor desirable.

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EVPN MPLS Service Types Illustrated

EVPN VLAN-Based Service

With this service interface, an EVPN instance consists of only a single broadcast domain (e.g., a single VLAN).  Therefore, there is a one-to-one mapping between a VID on this interface and a MAC-VRF. Since a MAC-VRF corresponds to a single VLAN, it consists of a single bridge table corresponding to that VLAN.

EVPN VLAN-Based Service
EVPN VLAN-Based Service

Click here for Juniper MX Configuration Example.

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EVPN MPLS Service Types

Broadcast Domains

(VLANs)

Bridge Table MAC VLAN to MAC-VRF Mapping Ethernet TAG ID VID Translation
VLAN-Based Service Single Single Can overlap between VLANs one-to-one 0 Egress PE
VLAN Bundle Service Multiple Single Unique for all VLANs many-to-one 0 Not Supported
Port-Based Service Multiple Single Unique for all VLAN many-to-one 0 Not Supported
VLAN-Aware Bundle Service Multiple One per VLAN Can overlap between VLANs many-to-one VID or normalized TAG ID

 

Supported
Port-Based VLAN-Aware Service Multiple One per VLAN Can overlap between VLANs many-to-one VID

 

Not Supported

For more information on EVPN, please refer to our other articles on this topic:

http://www.bgphelp.com/tag/evpn/

EVPN Type 4 (Ethernet Segment route) Explained

Ethernet Segment Routes are needed in multi-homing scenario and used for Designated Forwarder Election. Designated Forwarder is responsible for sending broadcast, unknown multicast and multicast (BUM) traffic to the CE on a particular Ethernet Segment.

RFC 7432 allows selecting a DF at the granularity of <ES, VLAN> for VLAN-based service and <ES, VLAN bundle> for VLAN-aware service. This enables load-balancing of BUM traffic at a VLAN or VLAN-bundle level.

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EVPN Type 3 (Inclusive Multicast Ethernet Tag route) Explained

Type 3 routes are required for Broadcast, Unknown Unicast and Multicast (BUM) traffic delivery across EVPN networks. Type 3 advertisements provide information about P-tunnels that should be used to send BUM traffic.

Without Type 3 advertisements, ingress router would not know how to deliver BUM traffic to other PE devices that comprise given EVPN instance.

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EVPN Type 2 (MAC/IP Advertisement route) Explained

Type 2 routes are used to advertise MAC addresses and IP addresses that might be associated with aforementioned MAC addresses.

In order to advertise Type 2 routes, PE needs to learn MAC addresses from the directly attached CEs. This is done via normal data-plane learning mechanisms. RFC 7432 also allows for MAC address learning via control plane interaction between PE and CE, although we have not see this implemented by any vendors.

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EVPN Type 1 (Ethernet Auto-Discovery) Explained

Type 1 advertisements are used for two distinct functions – Fast Convergence and Aliasing. EVPN Fast Convergence allows PE devices to change the next-hop adjacencies for all MAC addresses associated with a particular Ethernet Segment. EVPN aliasing allows traffic to be balanced across multiple egress points.

Type 1 routes are only advertised if Ethernet Segment Identifier is set to non-zero value, meaning that Type 1 routes are only originate for multi-homed sites.

Please refer to the following cheatsheet if you are not familiar with EVPN Terminology.

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EVPN Terminology Reference (RFC 7432, etc)

  • AC, A-C: Attachment Circuit
  • AD, A-D: Ethernet Auto-Discovery route
  • Ethernet Segment (ES): When a customer site (device or network) is connected to one or more PEs via a set of Ethernet links, then that set of links is referred to as an ‘Ethernet segment’.
  • Ethernet Segment Identifier (ESI): A unique non-zero identifier that identifies an Ethernet segment is called an ‘Ethernet Segment Identifier’. ESI 0 denotes a single-homed site.  ESI {0xFF} (repeated 10 times) is known as MAX-ESI.
  • Ethernet Tag: An Ethernet tag identifies a particular broadcast domain, e.g., a VLAN. An EVPN instance consists of one or more broadcast domains.
  • Ethernet Tag ID: 32-bit field containing either a 12-bit or 24-bit identifier that identifies a particular broadcast domain (e.g., a VLAN) in an EVPN instance.
  • EVI: An EVPN Instance spanning the Provider Edge (PE) devices participating in that EVPN.
  • EVPN: Ethernet Virtual Private Network.
  • IPL: IP address length
  • IRB: Integrated Routing and Bridging interface
  • NVE: Network Virtualization Edge
  • MAC-VRF: A Virtual Routing and Forwarding table for Media Access Control (MAC) addresses on a PE.
  • MAX-ET: Reserved Ethernet Tag ID {0xFFFFFFFF} is known as MAX-ET
  • MAX-ESI: Reserved ESI {0xFFFFFFFFFFFFFFFFFFFF} is known as MAX-ESI
  • ML: MAC address length
  • TS: Tenant System
  • VA: Virtual Appliance

MPLS VPN Service with Segment Routing

MPLS VPN Configuration example with IS-IS based Segment Routing (SPRING) on Juniper QFX5100 devices. The purpose of this lab is to demonstrate what LDP or RSVP-TE can be easily replaced with SR.

Complete Configuration Repository on GitHub:

https://github.com/bgphelp/blueprints/tree/master/SR/MPLS-VPN-SR-QFX5100

 
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