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    CE-Side MPLS L2VPNs over LAG Overview

    MPLS L2VPNs over link aggregation groups (LAGs) uses the functionality of both layer 2 services over MPLS and LAG. MPLS L2VPNs (Martini circuits) over LAG enable MPLS Martini circuits to use LAG in the network between the customer edge (CE) devices and the provider edge (PE) routers to distribute traffic arriving from pseudowires across multiple physical Ethernet interfaces. The criteria for distribution of packets that are transmitted from the pseudowires across the LAG bundle are determined by the hashing of VLAN and the source and destination MAC addresses. If a packet contains a VLAN stack, all the VLAN identifiers of the received packet, the source MAC address, and the destination MAC address are used in the hashing algorithm. If the packet does not contain a VLAN stack, only the source and destination MAC addresses are used in the hashing algorithm.

    Using MPLS L2VPNs over the LAGs configured between CE and PE devices provides redundancy and increased bandwidth on demand. The capability to use MPLS L2VPNs over LAG is available on GE-HDE, GE-2, and ES2 4G LM.

    Similarly, you can enable distribution of IP traffic from pseudowires across multiple physical interfaces on the PE routers facing the CE-side devices. In this case, the source and destination IP addresses are used in the hashing rule to determine the distribution criteria for received packets. You must use a different VLAN for IP packets from the one used for MPLS L2VPN packets. However, you can use the same LAG bundle that you configured for MPLS L2VPN traffic for IP traffic distribution.

    Figure 1 shows an example of an MPLS L2VPN or Martini tunnel over LAG on the CE-side device. A set of Ethernet ports on a provider edge device, PE1, are configured as member ports of LAG1. An MPLS L2VPN tunnel from PE1 to another provider edge device, PE2, is configured over an interface, VLAN1, over LAG1. An MPLS shim interface is stacked on the VLAN1 interface, when the MPLS L2VPN tunnel over VLAN1 over LAG1 is configured. The Martini tunnel from PE1 to PE2 can be configured either over Ethernet or LAG. In this scenario, it is considered to be configured over LAG.

    Figure 1: CE-Side MPLS L2VPN Tunnel over LAG

    CE-Side MPLS L2VPN
Tunnel over LAG

    Layer 2 frames arrive from CE1 to PE1 on the VLAN1 interface that resides below the MPLS shim interface. These frames are encapsulated in an MPLS packet and forwarded to the MPLS next hop. The attributes of the shim interface are used to determine the encapsulation parameters. These MPLS packets are later forwarded to the remote PE2 device. PE2 processes all the MPLS labels and determines that layer 2 processing is required on the remaining layer 2 frames. After PE2 processes the Ethernet layer 2 frames, they are forwarded to CE2.

    Traffic arriving at PE1 from pseudowires is distributed across all the member links of the LAG. The hashing algorithm, based on the VLAN identifier and source and destination MAC addresses, is used to determine the physical link to which the packets must be forwarded.

    If you configure the Martini tunnel directly over LAG in the same topology as shown in Figure 1, packet processing at PE1 remains the same as the case described. The only difference is in processing the hash algorithm, which uses only the source and destination MAC addresses, and not the VLAN identifier, to determine the physical link for transmission of MPLS packets transmitted from the pseudowires.

    If IP traffic is being transmitted from CE1, which is not designated for the MPLS L2VPN tunnel, the packets arrive at an interface that is different from the one used for MPLS traffic, VLAN2. This behavior occurs because the VLAN interface used for transmission of IP traffic must be different from that used for MPLS traffic.

    The MPLS shim interface can be configured directly over LAG or stacked on a VLAN interface over LAG. For more information on the guidelines to be followed when you configure the MPLS shim interface to enable MPLS Martini circuits to use LAG on the CE-side devices, see Multiple Layer 2 Services over MPLS Overview.

    Published: 2014-08-18