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EVPN-MH Configuration#

In this part, we will focus on configuration tasks required to enable multihoming in our fabric.

EVPN-MH configuration touches Ethernet Segment (ES) peers. ES peer is a leaf that has links to a multihomed host. In our case leaf1 and leaf2 are ES peers, because CE1 is connected to both of them.

The following items need to be configured on ES Peers:

  • A LAG and member interfaces
  • Ethernet segment
  • MAC-VRF interface mapping

Remember that the lab is pre-configured with fabric underlay, EVPN, and a MAC-VRF for CE-to-CE L2 reachability.


For an all-active multihoming SR Linux nodes need to be configured with a LAG interface facing the CE.

LAG between PEs and CE

The following configuration snippet can be pasted in the CLI of leaf1 and leaf2 to create a logical LAG interface lag1 with LACP support.

enter candidate
    /interface lag1 {
        admin-state enable
        vlan-tagging true
        subinterface 0 {
            type bridged
            vlan {
                encap {
                    untagged {
        lag {
            lag-type lacp
            member-speed 10G
            lacp {
                interval SLOW
                lacp-mode ACTIVE
                admin-key 11
                system-id-mac 00:00:00:00:00:11
                system-priority 11
commit now

The lag1 interface was created with vlan-tagging enabled that allows multiple subinterfaces with different VLAN tags to use it. This way each subinterface can be connected to a different MAC-VRF.
Subinterface 0 has been added to lag1 with untagged encapsulation.

The lag type can be LACP or static. For this lab we chose to use LACP for our LAG, so LACP parameters must match in all ES-peer nodes - leaf1 and leaf2.

And finally, we bind the physical interface(s) to the logical LAG interface to complete the LAG configuration part.

enter candidate
    /interface ethernet-1/1 {
        admin-state enable
        ethernet {
            aggregate-id lag1
commit now

As shown in config snippet above, the physical interface ethernet-1/1 will be part of lag1 interface on both leaf1 and leaf2 nodes.

All PEs that provide multihoming to a CE must be similarly configured with the lag and interface configurations.

Ethernet Segment#

When a CE device is connected to one or more PEs via a set of Ethernet links, then this set of Ethernet links constitutes an "Ethernet segment". This is a key concept of EVPN Multihoming.

In SR Linux, the ethernet segments are configured under the system network-instance protocols context.

ES configuration applied on both leaf1 and leaf2
enter candidate
/system network-instance protocols 
    evpn {
        ethernet-segments {
            bgp-instance 1 {
                ethernet-segment ES-1 {
                    admin-state enable
                    esi 01:11:11:11:11:11:11:00:00:01
                    multi-homing-mode all-active
                    interface lag1 {
    bgp-vpn {
        bgp-instance 1 {
commit now

The ethernet-segment is created with a name ES-1 under bgp-instance 1 with the all-active mode.

For a multihomed site, each Ethernet segment (ES) is identified by a unique non-zero identifier called an Ethernet Segment Identifier (ESI).
An ESI is encoded as a 10-octet integer in line format with the most significant octet sent first.

The esi and multi-homing-mode must match in all ES peers. At last, we assign the interface lag1 to ES-1.

Besides the ethernet segments, bgp-vpn is also configured with bgp-instance 1 to use the BGP information (RT/RD) for the ES routes exchanged in EVPN to enable multihoming.

MAC-VRF Interface#

Typically, an L2 multi-homed LAG subinterface needs to be associated with a MAC-VRF.

MAC-VRF interface configuration applied on both leaf1 and leaf2
enter candidate
    /network-instance mac-vrf-1 {
        interface lag1.0 {
commit now

To provide the load-balancing for all-active multihoming segments, set ecmp to the expected number of leaves (PE) serving the CE1.
Since we have two leaves connected to CE1, we set ecmp 2.

MAC-VRF ECMP configuration applied on all, leaf1, leaf2 and leaf3.
enter candidate
    /network-instance mac-vrf-1 {
        protocols {
            bgp-evpn {
                bgp-instance 1 {
                    ecmp 2
commit now

The entire MAC-VRF with VXLAN configuration is covered here.

This completes an all-active EVPN-MH configuration. Now let's have a look at the multihomed CE1 host and its configuration.

Customer Edge Device#

To create a multihomed connection, our CE1 emulated host has a bond0 interface configured with interfaces eth1 and eth2 underneath. Similar to the SR Linux part, it is configured with LACP (802.3ad).

The single-homed CE2 has multiple interfaces to a single leaf3 switch. These interfaces are placed in different VRFs so that CE2 can simulate multiple remote endpoints.

Multiple IP hosts in CE2

Below are the CE interface configurations that are executed by containerlab during the deployment.

# creating bond interface w/LACP
ip link add bond0 type bond mode 802.3ad
ip link set address 00:c1:ab:00:00:11 dev bond0
ip addr add dev bond0
ip link set eth1 down 
ip link set eth2 down
ip link set eth1 master bond0
ip link set eth2 master bond0
ip link set eth1 up 
ip link set eth2 up  
ip link set bond0 up
# setting three isolated (w/vrfs) interfaces
# with IPs from the same subnet 
# to simulate multiple remote clients in one container.
ip link set address 00:c1:ab:00:00:21 dev eth1
ip link set address 00:c1:ab:00:00:22 dev eth2
ip link set address 00:c1:ab:00:00:23 dev eth3
ip link add dev vrf-1 type vrf table 1
ip link set dev vrf-1 up
ip link set dev eth1 master vrf-1
ip link add dev vrf-2 type vrf table 2
ip link set dev vrf-2 up
ip link set dev eth2 master vrf-2
ip link add dev vrf-3 type vrf table 3
ip link set dev vrf-3 up
ip link set dev eth3 master vrf-3
ip addr add dev eth1
ip addr add dev eth2
ip addr add dev eth3

This is primarily to get better entropy for load balancing, so you can observe CE1 sending/receiving packets to/from both PEs, as shown below.

CE connections to mac-vrf-1 network instance

Now, let's see how EVPN-MH control plane works and which commands you can use to verify the configuration.

  1. An Ethernet segment can span up to four provider edge (PE) routers.