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.

Type 2 route format is shown below. Route Distinguisher, ESI, Ethernet TAG ID and MAC information are mandatory.

EVPN Type 2 Route
EVPN Type 2 Route

IP Address field is optional and is set to zero by default. This field might be populated if PE is aware of an IP address associated with a given MAC address. This is used in proxy ARP scenarios, where remote PE will respond to an ARP request received from a CE attached to that PE.

MPLS Label1 field is mandatory downstream-assigned Label associated with the MAC address being advertised by a PE. This label is used to forward packets toward the CE.

RFC 7432 specifies four label assignment mechanisms:

Assignment Mechanism Description
MAC-VRF Single EVPN label for all MAC addresses in a given MAC-VRF
MAC-VRF, Ethernet tag Unique EVPN label per <MAC-VRF, Ethernet tag> combination

 

ESI, Ethernet tag Unique EVPN label per <ESI, Ethernet tag> combination
MAC Unique EVPN label per MAC address

Please refer to EVPN Terminology document if you are not familiar with above terms.

Let’s review Type 2 advertisements originated by PE5 for CE4 site in the following topology:

EVPN MPLS Type 1 For Topology Diagram (RFC 7432 Explained)
EVPN MPLS Type 1 Topology Diagram

PE5’s configuration for CE4 site in Juniper format:

interfaces {
    ge-0/0/1 {
        description CE4;
        flexible-vlan-tagging;
        encapsulation flexible-ethernet-services;
        unit 100 {
            encapsulation vlan-bridge;
            vlan-id 100;
        }
    }
}

routing-instances {
    BD100 {
        instance-type evpn;
        vlan-id 100;
        interface ge-0/0/1.100;
        interface ge-0/0/2.100;
        route-distinguisher 120.0.2.5:100;
        vrf-target target:100:100;
        protocols {
            evpn;
        }
    }
}

The following Wireshark capture demonstrates PE5’s advertisement of CE4’s MAC address:

        Path Attribute - MP_REACH_NLRI
            Flags: 0x90, Optional, Length: Optional, Non-transitive, Complete, Extended Length
            Type Code: MP_REACH_NLRI (14)
            Length: 71
            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 (62 bytes)


                EVPN NLRI: MAC Advertisement Route
                    AFI: MAC Advertisement Route (2)
                    Length: 33
                    Route Distinguisher: 0001780002050064 (120.0.2.5:100)
                    ESI: 00 00 00 00 00 00 00 00 00
                        ESI Type: ESI 9 bytes value (0)
                        ESI 9 bytes value: 00 00 00 00 00 00 00 00 00
                    Ethernet Tag ID: 100
                    MAC Address Length: 48
                    MAC Address: 00:0c:29:82:c2:a9
                    IP Address Length: 0
                    IP Address: NOT INCLUDED
                    MPLS Label Stack: 299776 (bottom)

Type 2 route as observed on PE5:

* 2:120.0.2.5:100::100::00:0c:29:82:c2:a9/304 MAC/IP (1 entry, 1 announced)

 BGP group IBGP-RR type Internal
     Route Distinguisher: 120.0.2.5:100
     Route Label: 299776
     ESI: 00:00:00:00:00:00:00:00:00:00
     Nexthop: Self
     Flags: Nexthop Change
     Localpref: 100
     AS path: [100] I
     Communities: target:100:100

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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