Virtual Private LAN Service (VPLS) allows Multiprotocol Label Switching (MPLS) networks to provide multipoint Ethernet LAN services, also known as Transparent LAN Services (TLS). All customer sites in a VPLS appear to be on the same LAN, even though these sites might be in different geographic locations.

VPLS Autodiscovery enables each Virtual Private LAN Service (VPLS) provider edge (PE) device to discover other PE devices that are part of the same VPLS domain. VPLS Autodiscovery also tracks PE devices when they are added to or removed from a VPLS domain. Autodiscovery and signaling functions use the Border Gateway Protocol (BGP) to find and track PE devices.

BGP uses the Layer 2 VPN (L2VPN) Routing Information Base (RIB) to store endpoint provisioning information, which is updated each time any Layer 2 virtual forwarding instance (VFI) is configured. The prefix and path information is stored in the L2VPN database, which allows BGP to make decisions about the best path. When BGP distributes the endpoint provisioning information in an update message to all its BGP neighbors, this endpoint information is used to configure a pseudowire mesh to support L2VPN-based services.

The BGP autodiscovery mechanism facilitates the configuration of L2VPN services, which are an integral part of the VPLS feature. VPLS enables flexibility in deploying services by connecting geographically dispersed sites as a large LAN over high-speed Ethernet in a robust and scalable IP Multiprotocol Label Switching (MPLS) network. For more information about BGP and the L2VPN address family in relation to VPLS Autodiscovery, see the following chapters in the IP Routing: BGP Configuration Guide:

• “L2VPN Address Family” section in the “Cisco BGP Overview” chapter
• “BGP Support for the L2VPN Address Family” chapter

With VPLS Autodiscovery enabled, you no longer need to manually set up Virtual Private LAN Service (VPLS). The commands that you use to set up VPLS Autodiscovery are similar to those that you use to manually configure VPLS, as shown in the table below. VPLS Autodiscovery uses neighbor commands in L2VPN address family mode to distribute endpoint information to configure a pseudowire.

l2 vfi vpls1 manual
 vpn id 100
 neighbor 10.10.10.1 encapsulation mpls
 neighbor 10.10.10.0 encapsulation mpls
 exit

l2 vfi vpls1 autodiscovery
 vpn id 100
 exit
router bgp 1
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 bgp update-delay 1
 neighbor 10.1.1.2 remote-as 1
 neighbor 10.1.1.2 update-source Loopback1  
 .
 .
 .
 address-family l2vpn vpls
 neighbor 10.1.1.2 activate
 neighbor 10.1.1.2 send-community extended  
exit-address-family 

Configure VPLS Autodiscovery by using the l2 vfi autodiscovery command. This command allows a virtual forwarding instance (VFI) to learn and advertise pseudowire endpoints. As a result, you no longer need to enter the neighbor command in L2 VFI configuration mode.

However, the neighbor command is still supported with VPLS Autodiscovery in L2 VFI configuration mode. You can use the neighbor command to allow PE devices that do not participate in the autodiscovery process to join the VPLS domain. You can also use the neighbor command with PE devices that have been configured using the Tunnel Selection feature. In addition, you can use the neighbor command in hierarchical VPLS configurations that have user-facing PE (U-PE) devices that do not participate in the autodiscovery process and have split-horizon forwarding disabled.

The following show commands were enhanced for VPLS Autodiscovery:

• The show mpls l2transport vc detail command was updated to include Forwarding Equivalence Class (FEC) 129 signaling information for autodiscovered Virtual Private LAN Service (VPLS) pseudowires.
• The show vfi command was enhanced to display information related to autodiscovered virtual forwarding instances (VFIs). The new output includes the VPLS ID, the route distinguisher (RD), the route target (RT), and router IDs of discovered peers.
• The show xconnect command was updated with the rib keyword to provide Routing Information Base (RIB) information about pseudowires.

By default, routes received from an internal BGP (iBGP) peer are not sent to another iBGP peer unless a full mesh configuration is formed between all BGP devices within an autonomous system (AS). This results in scalability issues. Using Border Gateway Protocol (BGP) route reflectors leads to much higher levels of scalability. Configuring a route reflector allows a device to advertise or reflect the iBGP learned routes to other iBGP speakers.

Virtual Private LAN Service (VPLS) Autodiscovery supports BGP route reflectors. A BGP route reflector can be used to reflect BGP VPLS prefixes without VPLS being explicitly configured on the route reflector.

A route reflector does not participate in autodiscovery; that is, no pseudowires are set up between the route reflector and the PE devices. A route reflector reflects VPLS prefixes to other PE devices so that these PE devices do not need to have a full mesh of BGP sessions. The network administrator configures only the BGP VPLS address family on a route reflector. For an example configuration of VPLS Autodiscovery support on a route reflector, see the “Example: BGP VPLS Autodiscovery Support on Route Reflector” section.