Ethernet VPN (EVPN) is a solution that provides Ethernet multipoint services over MPLS networks. EVPN operates in contrast to the existing Virtual Private LAN Service (VPLS) by enabling control-plane based MAC learning in the core. In EVPN, PEs participating in the EVPN instances learn customer MAC routes in control-plane using MP-BGP protocol. Control-plane MAC learning brings a number of benefits that allow EVPN to address the VPLS shortcomings, including support for multihoming with per-flow load balancing.

EVPN provides the solution for network operators for the following emerging needs in their network:

• Data center interconnect operation (DCI)

• Cloud and services virtualization

• Remove protocols and network simplification

• Integration of L2 and L3 services over the same VPN

• Flexible service and workload placement

• Multi-tenancy with L2 and L3 VPN

• Optimal forwarding and workload mobility

• Fast convergence

• Efficient bandwidth utilization

To implement EVPN features, you need to understand the following concepts:

• Ethernet Segment (ES): An Ethernet segment is a set of Ethernet links that connects a multihomed device. If a multi-homed device or network is connected to two or more PEs through a set of Ethernet links, then that set of links is referred to as an Ethernet segment. The Ethernet segment route is also referred to as Route Type 4. This route is used for designated forwarder (DF) election for BUM traffic.

• Ethernet Segment Identifier (ESI): Ethernet segments are assigned a unique non-zero identifier, which is called an Ethernet Segment Identifier (ESI). ESI represents each Ethernet segment uniquely across the network.

• EVI: The EVPN instance (EVI) is represented by the virtual network identifier (VNI). An EVI represents a VPN on a PE router. It serves the same role of an IP VPN Routing and Forwarding (VRF), and EVIs are assigned import/export Route Targets (RTs). Depending on the service multiplexing behaviors at the User to Network Interface (UNI), all traffic on a port (all-to-one bundling), or traffic on a VLAN (one-to-one mapping), or traffic on a list/range of VLANs (selective bundling) can be mapped to a Bridge Domain (BD). This BD is then associated to an EVI for forwarding towards the MPLS core.

• EAD/ES: Ethernet Auto Discovery Route per ES is also referred to as Route Type 1. This route is used to converge the traffic faster during access failure scenarios. This route has Ethernet Tag of 0xFFFFFFFF.

• EAD/EVI: Ethernet Auto Discovery Route per EVI is also referred to as Route Type 1. This route is used for aliasing and load balancing when the traffic only hashes to one of the switches. This route cannot have Ethernet tag value of 0xFFFFFF to differentiate it from the EAD/ES route.

• Aliasing: It is used for load balancing the traffic to all the connected switches for a given Ethernet segment using the Route Type 1 EAD/EVI route. This is done irrespective of the switch where the hosts are actually learned.

• Mass Withdrawal: It is used for fast convergence during the access failure scenarios using the Route Type 1 EAD/ES route.

• DF Election: It is used to prevent forwarding of the loops. Only a single router is allowed to decapsulate and forward the traffic for a given Ethernet Segment.

At startup, PEs exchange EVPN routes in order to advertise the following:

• VPN membership: The PE discovers all remote PE members of a given EVI. In the case of a multicast ingress replication model, this information is used to build the PEs flood list associated with an EVI. BUM labels and unicast labels are exchanged when MAC addresses are learned.

• Ethernet segment reachability: In multihoming scenarios, the PE auto-discovers remote PE and their corresponding redundancy mode (all-active or single-active). In case of segment failures, PEs withdraw the routes used at this stage in order to trigger fast convergence by signaling a MAC mass withdrawal on remote PEs.

• Redundancy Group membership: PEs connected to the same Ethernet segment (multihoming) automatically discover each other and elect a Designated Forwarder (DF) that is responsible for forwarding Broadcast, Unknown unicast and Multicast (BUM) traffic for a given EVI.

EVPN can operate in single-homing or dual-homing mode. Consider single-homing scenario, when EVPN is enabled on PE, Route Type 3 is advertised where each PE discovers all other member PEs for a given EVPN instance. When an unknown unicast (or BUM) MAC is received on the PE, it is advertised as EVPN Route Type 2 to other PEs. MAC routes are advertised to the other PEs using EVPN Route Type 2. In multihoming scenarios, Route Types 1, 3, and 4 are advertised to discover other PEs and their redundancy modes (single-active or all-active). Use of Route Type 1 is to auto-discover other PE which hosts the same CE. The other use of this route type is to fast route unicast traffic away from a broken link between CE and PE. Route Type 4 is used for electing designated forwarder. For instance, consider the topology when customer traffic arrives at the PE, EVPN MAC advertisement routes distribute reachability information over the core for each customer MAC address learned on local Ethernet segments. Each EVPN MAC route announces the customer MAC address and the Ethernet segment associated with the port where the MAC was learned from and its associated MPLS label. This EVPN MPLS label is used later by remote PEs when sending traffic destined to the advertised MAC address.

The EVPN network layer reachability information (NLRI) provides different route types.

Route Type 5: IP Prefix Route

The IP prefixes are advertised independently of the MAC-advertised routes. With EVPN IRB, host route /32 is advertised using RT-2 and subnet /24 is advertised using RT-5.

Note	With EVPN IRB, host route /32 are advertised using RT-2 and subnet /24 are advertised using RT-5.

To configure EVPN MAC address limit, the following restrictions are applicable:

• Remote MAC addresses are programmed in the hardware irrespective of whether the MAC address limit is configured or not.

• MAC address limit can be modified correctly only when the device is not actively learning any MAC addresses. This is an expected behavior.

• When the MAC learning is enabled, you can configure the MAC address limit up to a maximum of six. However, when the MAC learning is disabled, you can configure the MAC address limit up to a maximum of five.

• The clear l2vpn mac address table command is not supported. The MAC address table is cleared when shut or no shutdown is performed on an attachment circuit interface or sub interface, or when the MAC aging timer expires.

• You can configure both MAC limit Action and MAC notification. However, the configuration does not take into effect as the functionality is not supported.

Router# configure 
Router(config)# l2vpn 
Router(config-l2vpn)# bridge group EVPN-BG-SH
Router(config-l2vpn-bg)# bridge-domain EVPN_2701
Router(config-l2vpn-bg-bd)# mac
Router(config-l2vpn-bg-bd-mac)# limit
Router(config-l2vpn-bg-bd-mac-limit)# maximum 50
Router(config-l2vpn-bg-bd-mac-limit)#  exit
Router(config-l2vpn-bg-bd)#  exit
Router(config-l2vpn-bg)# exit
Router(config-l2vpn)# mac limit threshold 80
Router(config-l2vpn)# commit

l2vpn
bridge group EVPN-BG-SH
  bridge-domain EVPN_2701
   mac
    limit
     maximum 50
    !
   !
!
mac limit threshold 80
commit

Router# show l2vpn bridge-domain bd-name EVPN_2701 detail
Legend: pp = Partially Programmed.
Bridge group: EVPN-BG-SH, bridge-domain: EVPN_2701, id: 25, state: up, ShgId: 0, MSTi: 0
  Coupled state: disabled
  VINE state: EVPN Native
  MAC learning: enabled
  MAC withdraw: enabled
    MAC withdraw for Access PW: enabled
    MAC withdraw sent on: bridge port up
    MAC withdraw relaying (access to access): disabled
  Flooding:
    Broadcast & Multicast: enabled
    Unknown unicast: enabled
  MAC aging time: 300 s, Type: inactivity
  MAC limit: 50, Action: none, Notification: syslog
  MAC limit reached: no, threshold: 80%
  MAC port down flush: enabled
  MAC Secure: disabled, Logging: disabled
  Split Horizon Group: none
  Dynamic ARP Inspection: disabled, Logging: disabled
  IP Source Guard: disabled, Logging: disabled
  DHCPv4 Snooping: disabled
  DHCPv4 Snooping profile: none
  IGMP Snooping: disabled
  IGMP Snooping profile: none
  MLD Snooping profile: none
  Storm Control: disabled
  Bridge MTU: 1500
  MIB cvplsConfigIndex: 26
  Filter MAC addresses:
  P2MP PW: disabled
  Create time: 21/04/2019 16:28:05 (2d23h ago)
  No status change since creation
  ACs: 1 (1 up), VFIs: 0, PWs: 0 (0 up), PBBs: 0 (0 up), VNIs: 0 (0 up)
  List of EVPNs:
    EVPN, state: up
      evi: 6101
      XC ID 0x8000040c
     Statistics:
       packets: received 0 (unicast 0), sent 0
       bytes: received 0 (unicast 0), sent 0
       MAC move: 0
  List of ACs:
    AC: Bundle-Ether101.2701, state is up, active in RG-ID 101
      Type VLAN; Num Ranges: 1
      Rewrite Tags: [1000, 2000]
      VLAN ranges: [2701, 2701]
      MTU 9112; XC ID 0xa000060b; interworking none; MSTi 6
      MAC learning: enabled
      Flooding:
        Broadcast & Multicast: enabled
        Unknown unicast: enabled
      MAC aging time: 300 s, Type: inactivity
     MAC limit: 50, Action: none, Notification: syslog
      MAC limit reached: no, threshold: 80%
      MAC port down flush: enabled
      MAC Secure: disabled, Logging: disabled
      Split Horizon Group: none
      Dynamic ARP Inspection: disabled, Logging: disabled
      IP Source Guard: disabled, Logging: disabled
      DHCPv4 Snooping: disabled
      DHCPv4 Snooping profile: none
      IGMP Snooping: disabled
      IGMP Snooping profile: none
      MLD Snooping profile: none
      Storm Control:
        Broadcast: enabled(160000 pps)
        Multicast: enabled(160000 pps)
        Unknown unicast: enabled(160000 pps)
      Static MAC addresses:
      Statistics:
        packets: received 0 (multicast 0, broadcast 0, unknown unicast 0, unicast 0), sent 0
        bytes: received 0 (multicast 0, broadcast 0, unknown unicast 0, unicast 0), sent 0
        MAC move: 0
      Storm control drop counters: 
        packets: broadcast 0, multicast 0, unknown unicast 0 
        bytes: broadcast 0, multicast 0, unknown unicast 0 
      Dynamic ARP inspection drop counters: 
        packets: 0, bytes: 0
      IP source guard drop counters: 
        packets: 0, bytes: 0
  List of Access PWs:
  List of VFIs:
  List of Access VFIs:

The MAC addresses learned on one device needs to be learned or distributed on the other devices in a VLAN. EVPN Software MAC Learning feature enables the distribution of the MAC addresses learned on one device to the other devices connected to a network. The MAC addresses are learnt from the remote devices using BGP.

Note	A device can contain up to 128K MAC address entries. A bridge domain on a device can contain up to 64K MAC address entries.

The above figure illustrates the process of software MAC learning. The following are the steps involved in the process:

1. Traffic comes in on one port in the bridge domain.

2. The source MAC address (AA) is learnt on the PE and is stored as a dynamic MAC entry.

3. The MAC address (AA) is converted into a type-2 BGP route and is sent over BGP to all the remote PEs in the same EVI.

4. The MAC address (AA) is updated on the PE as a remote MAC address.

The EVPN Out of Service feature enables you to control the state of bundle interfaces that are part of an Ethernet segment that have Link Aggregation Control protocol (LACP) configured. This feature enables you to put a node out of service (OOS) without having to manually shutdown all the bundles on their provider edge (PE).

Use the cost-out command to bring down all the bundle interfaces belonging to an Ethernet VPN (EVPN) Ethernet segment on a node. The Ethernet A-D Ethernet Segment (ES-EAD) routes are withdrawn before shutting down the bundles. The PE signals to the connected customer edge (CE) device to bring down the corresponding bundle member. This steers away traffic from this PE node without traffic disruption. The traffic that is bound for the Ethernet segment from the CE is directed to the peer PE in a multi-homing environment.

Note	EVPN cost-out is supported only on manually configured ESIs.

In the following topology, the CE is connected to PE1 and PE2. When you configure the cost-out command on PE1, all the bundle interfaces on the Ethernet segment are brought down. Also, the corresponding bundle member is brought down on the CE. Hence, the traffic for this Ethernet segment is now sent to PE2 from the CE.

To bring up the node into service, use no cost-out command. This brings up all the bundle interfaces belonging to EVPN Ethernet segment on the PE and the corresponding bundle members on the CE.

When the node is in cost-out state, adding a new bundle Ethernet segment brings that bundle down. Similarly, removing the bundle Ethernet segment brings that bundle up.

Use startup-cost-in command to bring up the node into service after the specified time on reload. The node will cost-out when EVPN is initialized and remain cost-out until the set time. If you execute evpn no startup-cost-in command while timer is running, the timer stops and node is cost-in.

The 'cost-out' configuration always takes precedence over the 'startup-cost-in' timer. So, if you reload with both the configurations, cost-out state is controlled by the 'cost-out' configuration and the timer is not relevant. Similarly, if you reload with the startup timer, and configure 'cost-out' while timer is running, the timer is stopped and OOS state is controlled only by the 'cost-out' configuration.

If you do a proc restart while the startup-cost-in timer is running, the node remains in cost-out state and the timer restarts.

EVPN Multiple Services per Ethernet Segment feature allows you to configure multiple services over single Ethernet Segment (ES). Instead of configuring multiple services over multiple ES, you can configure multiple services over a single ES.

You can configure the following services on a single Ethernet Bundle; you can configure one service on each sub-interface.

• Flexible cross-connect (FXC) service. It supports VLAN Unaware, VLAN Aware, and Local Switching modes.

  For more information, see Configure Point-to-Point Layer 2 Services chapter in L2VPN and Ethernet Services Configuration Guide for Cisco NCS 5500 Series Routers.

• EVPN-VPWS Xconnect service

  For more information, see EVPN Virtual Private Wire Service (VPWS) chapter in L2VPN and Ethernet Services Configuration Guide for Cisco NCS 5500 Series Routers.

• EVPN Integrated Routing and Bridging (IRB)

  For more information, see Configure EVPN IRB chapter in L2VPN and Ethernet Services Configuration Guide for Cisco NCS 5500 Series Routers.

• Native EVPN

  For more information see, EVPN Features chapter in L2VPN and Ethernet Services Configuration Guide for Cisco NCS 5500 Series Routers.

All these services are supported only on all-active multihoming scenario.

Seamless integration of EVPN MPLS with VPLS enables the co-existence of PE nodes running EVPN and VPLS for the same VPN instance. VPLS or legacy network can be upgraded to the next generation EVPN network without service disruption. You can introduce EVPN service on all the selected VPLS provider edge (PE) nodes simultaneously. However, to avoid traffic disruption, provision EVPN service on existing VPLS-enabled PEs one by one.

The following examples show EVI configuration under L2VPN bridge-domain for various VPLS-based networks:

l2vpn
 bridge group bg1
  bridge-domain bd-1-1
   interface GigabitEthernet0/2/0/0.1
   !
   vfi vfi-1-1
    neighbor 200.0.2.1 pw-id 1200001
     mpls static label local 20001 remote 10001
    !
    neighbor 200.0.3.1 pw-id 1300001
     mpls static label local 30001 remote 10001
    !
    neighbor 200.0.4.1 pw-id 1400001
     mpls static label local 40001 remote 10001
    !   
  !
  evi 1 
!

l2vpn
bridge group bg1
bridge-domain bd-1-2
   interface GigabitEthernet0/2/0/0.2
   !
   vfi vfi-1-2
    vpn-id 2
    autodiscovery bgp
     rd 101:2
     route-target 65530:200
     signaling-protocol bgp
      ve-id 11
      ve-range 16
     !
    !
   evi 2
  !

bridge-domain bd-1-4
   interface GigabitEthernet0/2/0/0.4
   !
   vfi vfi-1-4
    neighbor 200.0.2.1 pw-id 1200004
    !
    neighbor 200.0.3.1 pw-id 1300004
    !
    neighbor 200.0.4.1 pw-id 1400004
    !
   evi 3
   !

Use the following commands to verify EVPN configuration and MAC advertisement. Verify EVPN status, AC status, and VFI status.

• show l2vpn bridge-domain

• show evpn summary

• show bgp rt l2vpn evpn

• show evpn evi

• show l2route evpn mac all

Router#show l2vpn bridge-domain bd-name bd-1-1
Mon Feb 20 21:03:40.244 EST
Legend: pp = Partially Programmed.
Bridge group: bg1, bridge-domain: bd-1-1, id: 0, state: up, ShgId: 0, MSTi: 0
  Aging: 300 s, MAC limit: 4000, Action: none, Notification: syslog
  Filter MAC addresses: 0
  ACs: 1 (1 up), VFIs: 1, PWs: 3 (2 up), PBBs: 0 (0 up), VNIs: 0 (0 up)
  List of EVPNs:
    EVPN, state: up
  List of ACs:
    Gi0/2/0/0.1, state: up, Static MAC addresses: 0, MSTi: 2
  List of Access PWs:
  List of VFIs:
    VFI vfi-1-1 (up)
      Neighbor 200.0.2.1 pw-id 1200001, state: up, Static MAC addresses: 0
      Neighbor 200.0.3.1 pw-id 1300001, state: down, Static MAC addresses: 0
      Neighbor 200.0.4.1 pw-id 1400001, state: up, Static MAC addresses: 0
  List of Access VFIs:
 When PEs are evpn enabled, pseudowires that are associated with that BD will be brought down. The VPLS BD pseudowires are always up.  

Verify the number of EVI’s configured, local and remote MAC-routes that are advertised.

Router#show evpn summary
Mon Feb 20 21:05:16.755 EST
-----------------------------
Global Information
-----------------------------
Number of EVIs                     : 6
Number of Local EAD Entries        : 0
Number of Remote EAD Entries       : 0
Number of Local MAC Routes         : 4
          MAC                      : 4
          MAC-IPv4                 : 0
          MAC-IPv6                 : 0
Number of Local ES:Global MAC      : 1
Number of Remote MAC Routes        : 0
          MAC                      : 0
          MAC-IPv4                 : 0
          MAC-IPv6                 : 0
Number of Remote SOO MAC Routes    : 0
Number of Local IMCAST Routes      : 4
Number of Remote IMCAST Routes     : 4
Number of Internal Labels          : 0
Number of ES Entries               : 1
Number of Neighbor Entries         : 4
EVPN Router ID                     : 200.0.1.1
BGP ASN                            : 65530
PBB BSA MAC address                : 0026.982b.c1e5
Global peering timer               :      3 seconds
Global recovery timer              :     30 seconds

Verify EVPN route-targets.

Router#show bgp rt l2vpn evpn
Mon Feb 20 21:06:18.882 EST
EXTCOMM         IMP/EXP
RT:65530:1               1 / 1
RT:65530:2               1 / 1
RT:65530:3               1 / 1
RT:65530:4               1 / 1
Processed 4 entries

Locally learnt MAC routes can be viewed by forwarding table 
show l2vpn forwarding bridge-domain mac-address location 0/0/cpu0
To Resynchronize MAC table from the Network Processors, use the command...
    l2vpn resynchronize forwarding mac-address-table location <r/s/i>

Mac Address    Type    Learned from/Filtered on    LC learned Resync Age/Last Change Mapped to       
-------------- ------- --------------------------- ---------- ----------------------
0033.0000.0001 dynamic Gi0/2/0/0.1                 N/A        20 Feb 21:06:59     N/A             
0033.0000.0002 dynamic Gi0/2/0/0.2                 N/A        20 Feb 21:06:59     N/A             
0033.0000.0003 dynamic Gi0/2/0/0.3                 N/A        20 Feb 21:04:29     N/A             
0033.0000.0004 dynamic Gi0/2/0/0.4                 N/A        20 Feb 21:06:59     N/A  

The remote routes learned via evpn enabled BD 
show l2vpn forwarding bridge-domain mac-address location 0/0$
To Resynchronize MAC table from the Network Processors, use the command...
    l2vpn resynchronize forwarding mac-address-table location <r/s/i>

Mac Address    Type    Learned from/Filtered on    LC learned Resync Age/Last Change Mapped to       
-------------- ------- --------------------------- ---------- ----------------------   
0033.0000.0001 EVPN    BD id: 0                    N/A        N/A                 N/A             
0033.0000.0002 EVPN    BD id: 1                    N/A        N/A                 N/A             
0033.0000.0003 EVPN    BD id: 2                    N/A        N/A                 N/A             
0033.0000.0004 EVPN    BD id: 3                    N/A        N/A                 N/A             

Verify EVPN MAC routes pertaining to specific VPN instance.

Router#show evpn evi vpn-id 1 mac
Mon Feb 20 21:36:23.574 EST

EVI        MAC address    IP address                   Nexthop                            Label   
---------- -------------- ---------------------------------------- ---------------------------------
1      0033.0000.0001      ::                       200.0.1.1                          45106

Verify L2 routing.

Router#show l2route evpn mac all
Mon Feb 20 21:39:43.953 EST
Topo ID  Mac Address    Prod   Next Hop(s)                             
-------- -------------- ------ ----------------------------------------
0        0033.0000.0001 L2VPN  200.0.1.1/45106/ME                      
1        0033.0000.0002 L2VPN  200.0.1.1/45108/ME                      
2        0033.0000.0003 L2VPN  200.0.1.1/45110/ME                      
3        0033.0000.0004 L2VPN  200.0.1.1/45112/ME   

Verifty EVPN route-type 2 routes.

Router#show bgp l2vpn evpn route-type 2
Mon Feb 20 21:43:23.616 EST
BGP router identifier 200.0.3.1, local AS number 65530
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0x0   RD version: 0
BGP main routing table version 21
BGP NSR Initial initsync version 1 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 200.0.1.1:1
*>i[2][0][48][0033.0000.0001][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:2
*>i[2][0][48][0033.0000.0002][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:3
*>i[2][0][48][0033.0000.0003][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:4
*>i[2][0][48][0033.0000.0004][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.3.1:1 (default for vrf bd-1-1)
*>i[2][0][48][0033.0000.0001][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.3.1:2 (default for vrf bd-1-2)
*>i[2][0][48][0033.0000.0002][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.3.1:3 (default for vrf bd-1-3)
*>i[2][0][48][0033.0000.0003][0]/104
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.3.1:4 (default for vrf bd-1-4)
*>i[2][0][48][0033.0000.0004][0]/104
                      200.0.1.1                     100      0 i

Processed 8 prefixes, 8 paths

Verify inclusive multicast routes and route-type 3 routes.

Router#show bgp l2vpn evpn route-type 3
Mon Feb 20 21:43:33.970 EST
BGP router identifier 200.0.3.1, local AS number 65530
BGP generic scan interval 60 secs
Non-stop routing is enabled
BGP table state: Active
Table ID: 0x0   RD version: 0
BGP main routing table version 21
BGP NSR Initial initsync version 1 (Reached)
BGP NSR/ISSU Sync-Group versions 0/0
BGP scan interval 60 secs

Status codes: s suppressed, d damped, h history, * valid, > best
              i - internal, r RIB-failure, S stale, N Nexthop-discard
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network            Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 200.0.1.1:1
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:2
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:3
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.1.1:4
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
Route Distinguisher: 200.0.3.1:1 (default for vrf bd-1-1)
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
*> [3][0][32][200.0.3.1]/80
                      0.0.0.0                                0 i
Route Distinguisher: 200.0.3.1:2 (default for vrf bd-1-2)
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
*> [3][0][32][200.0.3.1]/80
                      0.0.0.0                                0 i
Route Distinguisher: 200.0.3.1:3 (default for vrf bd-1-3)
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
*> [3][0][32][200.0.3.1]/80
                      0.0.0.0                                0 i
Route Distinguisher: 200.0.3.1:4 (default for vrf bd-1-4)
*>i[3][0][32][200.0.1.1]/80
                      200.0.1.1                     100      0 i
*> [3][0][32][200.0.3.1]/80
                      0.0.0.0                                0 i

The EVPN Core Isolation Protection feature enables you to monitor and detect the link failure in the core. When a core link failure is detected in the provider edge (PE) device, EVPN brings down the PE's Ethernet Segment (ES), which is associated with access interface attached to the customer edge (CE) device.

EVPN replaces ICCP in detecting the core isolation. This new feature eliminates the use of ICCP in the EVPN environment.

Consider a topology where CE is connected to PE1 and PE2. PE1, PE2, and PE3 are running EVPN over the MPLS core network. The core interfaces can be Gigabit Ethernet or bundle interface.

When the core links of PE1 go down, the EVPN detects the link failure and isolates PE1 node from the core network by bringing down the access network. This prevents CE from sending any traffic to PE1. Since BGP session also goes down, the BGP invalidates all the routes that were advertised by the failed PE. This causes the remote PE2 and PE3 to update their next-hop path-list and the MAC routes in the L2FIB. PE2 becomes the forwarder for all the traffic, thus isolating PE1 from the core network.

When all the core interfaces and BGP sessions come up, PE1 advertises Ethernet A-D Ethernet Segment (ES-EAD) routes again, triggers the service carving and becomes part of the core network.

The EVPN Routing Policy feature provides the route policy support for address-family L2VPN EVPN. This feature adds EVPN route filtering capabilities to the routing policy language (RPL). The filtering is based on various EVPN attributes.

A routing policy instructs the router to inspect routes, filter them, and potentially modify their attributes as they are accepted from a peer, advertised to a peer, or redistributed from one routing protocol to another.

This feature enables you to configure route-policies using EVPN network layer reachability information (NLRI) attributes of EVPN route type 1 to 5 in the route-policy match criteria, which provides more granular definition of route-policy. For example, you can specify a route-policy to be applied to only certain EVPN route-types or any combination of EVPN NLRI attributes. This feature provides flexibility in configuring and deploying solutions by enabling route-policy to filter on EVPN NLRI attributes.

For information on these concepts, see Implementing Routing Policy.

Currently, this feature is supported only on BGP neighbor "in" and "out" attach points. The route policy can be applied only on inbound or outbound on a BGP neighbor.

This feature includes a preference-based and access-driven DF election mechanism.

In a preference-based DF election mechanism, the weight decides which PE is the DF at any given time. You can use this method for topologies where interface failures are revertive. However, for topologies where an access-PE is directly connected to the core PE, use the access-driven DF election mechanism.

When access PEs are configured in a non-revertive mode, the access-driven DF election mechanism allows the access-PE to choose which PE is the DF.

Consider an interface in an access network that connects PE nodes running Multichassis Link Aggregation Control Protocol (mLACP) and the EVPN PE in the core. When this interface fails, there may be a traffic loss for a longer duration. The delay in convergence is because the backup PE is not chosen before failure occurs.

The EVPN Access-Driven DF Election feature allows the EVPN PE to preprogram a backup PE even before the failure of the interface. In the event of failure, the PE node will be aware of the next PE that will take over. Thereby reducing the convergence time. Use the preference df weight option for an Ethernet segment identifier (ESI) to set the backup path. By configuring the weight for a PE, you can control the DF election, thus define the backup path.

Topology

Let’s understand the feature on how the backup path is precomputed with the following topology.

• PE1, PE2, and PE3 are PEs for the EVPN core network.

• aPE1, aPE2, and aPE3 are their access PE counterparts and configured in a multichassis link aggregation group (MCLAG) redundancy group. Only one link among the three is active at any given time. aPE1, aPE2, and aPE3 are in a non-revertive mode.

• PE1 is directly connected to aPE1, PE2 to aPE2, and PE3 to aPE3. EVPN VPWS is configured on the PE devices in the core.

• All PE devices are attached to the same bundle and shares the same ethernet segment identifier.

• PE1, PE2, and PE3 are configured with a weight of 100, 10, and 1 respectively.

Traffic Flow

In this example, consider a traffic flow from a host connected to PE4 to the host connected to the access PE.

• aPE1-PE1 interface state is up. The aPE2-PE2 and aPE3-PE3 remains in OOS state.

• The traffic is sent from PE4 to aPE1 through PE1 as the PE1 is configured with a highest weight of 100.

• The highest weight is modified by adding 32768 to the configured weight. For example, the weight of PE1 is 100, 32768 is added to this weight. Hence, 32868 is advertised to the peer PEs.

• The highest weight is advertised as P-bit, which is primary. The next highest weight is advertised as B-bit, which is secondary. The lowest weight as non-DF (NDF).

• When the EVPN PE devcies are of same weight, the traffic is sent based on the IP address. Lowest IP address takes the precedence.

• Only one PE indicates that the state of the bundle for the Ethernet Segment is up. For all other PEs, the Ethernet Segment is standby and the bundle is in OOS state.

• All PE devices are aware of the associated next hop and weights of their peers.

Failure and Recovery Scenarios

The weights configured on the EVPN PE devices cascade in the same order as the protection mechanism on the access side PEs:

• During the network failure, the redundancy ordering for the access PEs is aPE1, aPE2, aPE3.

• The weights of PE1 through PE3 are weight of PE1 > weight of PE2 > weight of PE3.

• If this ordering is not satisfied, the network will eventually converge, but it will not be as efficient as if the weights are ordered correctly.

Scenario - 1

Consider a scenario where the aPE1-PE1 interface is down.

When aPE1-PE1 interface is down, the PE1 withdraws the EAD/ES route, and the traffic is sent through the backup path, which is PE2.

The aPE2-PE2 becomes the primary with a weight of 32778, and aPE3-PE3 becomes the backup. The aPE2-PE2 advertises P-bit to PE4. aPE3-PE3 advertises the B-bit to PE4.

Scenario - 2

Consider a scenario where aPE2-PE2 interface is also down.

When the aPE2-PE2 interface is also down, the traffic is sent through aPE3-PE3 link. aPE3-PE3 becomes the primary path with a weight of 32769.

Scenario - 3

When the aPE2-PE2 interface comes up, the aPE3-PE3 link still remains the primary path. aPE2-PE2 interface becomes the backup path with a weight of 10.

Scenario - 4

When the aPE1-PE1 interface comes up, the aPE3-PE3 link remains the primary path with a weight of 32769. aPE1-PE1 interface becomes the backup path with a weight of 100. The aPE2-PE2 interface becomes NDF with a weight of 10.