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.

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

The format of Type 4 advertisement is as follows:

EVPN Type 3 Route Format
EVPN Type 3 Route Format

Let’s review Type 4 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 4 route:

        Path Attribute - MP_REACH_NLRI
            Flags: 0x90, Optional, Length: Optional, Non-transitive, Complete, Extended Length
                1... .... = Optional: Optional
                .0.. .... = Transitive: Non-transitive
                ..0. .... = Partial: Complete
                ...1 .... = Length: Extended length
            Type Code: MP_REACH_NLRI (14)
            Length: 34
            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 (25 bytes)
                EVPN NLRI: Ethernet Segment Route
                    AFI: Ethernet Segment Route (4)
                    Length: 23
                    Route Distinguisher: 0001780002050000 (
                    ESI: 00 00 00 00 00 10 00 00 05
                        ESI Type: ESI 9 bytes value (0)
                        ESI 9 bytes value: 00 00 00 00 00 10 00 00 05
                    IP Address Length: 32
                    IPv4 address:

Advertised Type 4 route as observed on PE5:

* 4: ES (1 entry, 1 announced)
 BGP group IBGP-RR type Internal
     Route Distinguisher:
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: [100] I
     Communities: es-import-target:0-0-0-0-0-10

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:


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