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.

The format of Type 3 advertisement is as follows:

EVPN Type 3 Route
EVPN Type 3 Route

RFC allows for both ingress replication and network-based point-to-multipoint replication as defined in RFC 7117.

Type 3 route must also carry a Provider Multicast Service Interface (PMSI) Tunnel attribute as specified in RFC 6514.

Multicast PMSI Attribute
Multicast PMSI Attribute

At the moment, only one Flag is defined – Leaf Information Required (L).

The following Tunnel Types are defined, although your vendor might only support a subset of  tunnel types:

  • 0 – No tunnel information present
  • 1 – RSVP-TE P2MP LSP
  • 2 – mLDP P2MP LSP
  • 3 – PIM-SSM Tree
  • 4 – PIM-SM Tree
  • 5 – BIDIR-PIM Tree
  • 6 – Ingress Replication
  • 7 – mLDP MP2MP LSP

Let’s review Type 3 advertisements originated by PE5 in the following example:

EVPN MPLS Topology Diagram (RFC 7432 Explained)
EVPN MPLS Topology Diagram

 

The following Wireshark capture demonstrates PE5’s advertisement of Type 3 route:

       Path Attribute - PMSI_TUNNEL_ATTRIBUTE
            Flags: 0xc0, Optional, Transitive: Optional, Transitive, Complete
            Type Code: PMSI_TUNNEL_ATTRIBUTE (22)
            Length: 9
            Flags: 0
            Tunnel Type: Ingress Replication (6)
            0100 1001 0011 0110 0000 .... = MPLS Label: 299872
            Tunnel ID: tunnel end point -> 120.0.2.5
        Path Attribute - MP_REACH_NLRI
            Flags: 0x90, Optional, Length: Optional, Non-transitive, Complete, Extended Length
            Type Code: MP_REACH_NLRI (14)
            Length: 28
            Address family identifier (AFI): Layer-2 VPN (25)
            Subsequent address family identifier (SAFI): EVPN (70)
            Next hop network address (4 bytes)
            Number of Subnetwork points of attachment (SNPA): 0
            Network layer reachability information (19 bytes)
                EVPN NLRI: Inclusive Multicast Route
                    AFI: Inclusive Multicast Route (3)
                    Length: 17
                    Route Distinguisher: 0001780002050064 (120.0.2.5:100)
                    Ethernet Tag ID: 100
                    IP Address Length: 32
                    IPv4 address: 120.0.2.5
 

* 3:120.0.2.1:100::100::120.0.2.1/304 IM (1 entry, 1 announced)
 BGP group IBGP-RR type Internal
     Route Distinguisher: 120.0.2.1:100
     Route Label: 299872
     PMSI: Flags 0x0: Label 299872: Type INGRESS-REPLICATION 120.0.2.1
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: [100] I
     Communities: target:100:100
     PMSI: Flags 0x0: Label 299872: Type INGRESS-REPLICATION 120.0.2.1

Advertised Type 3 route as observed on PE5:

root@PE5> show route advertising-protocol bgp 120.0.1.1 extensive
* 3:120.0.2.5:100::100::120.0.2.5/304 IM (1 entry, 1 announced)
 BGP group IBGP-RR type Internal
     Route Distinguisher: 120.0.2.5:100
     Route Label: 315248
     PMSI: Flags 0x0: Label 315248: Type INGRESS-REPLICATION 120.0.2.5
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: [100] I
     Communities: target:100:100
     PMSI: Flags 0x0: Label 315248: Type INGRESS-REPLICATION 120.0.2.5

Control Plane Wireshark capture can be downloaded from GitHub:

EVPN Control Plane PCAP

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

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

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