8 – Extended Layer 2 over Layer 3 (L2 over L3) – MPLS


For point-to-point networks across very long distances, Ethernet over Multiprotocol Label Switching (EoMPLS) Pseudowire can be useful. The EoMPLS service is supported natively on Cisco Catalyst 6500 Series Switches with the Sup720 and Sup2T cards. In conjunction with the VSS function (clustered switches), the resiliency of the L2 VPN service can be easily improved for a DCI LAN extension. VSS provides a fully-redundant physical solution that enables a logical L2 over L3 link (Pseudowire) flawlessly and without the need to activate the Spanning Tree protocol between the remote sites. EoMPLS is also supported on Cisco ASR1000 Series Routers. L2 over L3 extends the Layer 2 Pseudowire over unlimited distances.

With an additional SIP or ES+ card on the Catalyst 6500, the EoMPLS function can be encapsulated directly into a GRE tunnel. This gives the option to extend the Layer 2 VPN over a pure IP network. In this case, the technical knowledge and experience required for an MPLS environment is no longer imposed. In addition, the GRE tunnel may be encrypted using the standard point-to-point encapsulation method of IPSec.

For Multiple data center interconnections, Cisco offers two technologies to address the requirements of cloud computing:

  • VPLS
  • OTV

Virtual Private LAN Service (VPLS) is available via two approaches:

  • A-VPLS: Advanced VPLS (A-VPLS) is designed for enterprise environments. A-VPLS is available on Cisco Catalyst 6500 Series Switches using a SIP-400 or ES+ WAN card10. This option takes advantage of the system virtualization capabilities of the Catalyst 6500 VSS so that all physical links and edge switches are redundant and active without extending the Spanning Tree protocol between sites. A-VPLS has been specifically designed to offer simplicity of implementation with all the features and performance of the MPLS transport protocol. This feature can also be implemented on a pure IP core network via a GRE tunnel.
  • H-VPLS: H-VPLS is designed for service provider environments, in which very high capacity interconnections and segmentation are required. It can process information in very large private, public and hybrid cloud environments with large numbers of multi-tenants. H-VPLS is available with the Cisco ASR9000 Series Routers.Chassis Link Aggregation Group (MC-LAG)MC-LAG enables downstream devices to dual-home one or more bundles of links using the Link Aggregation Control Protocol (LACP) 802.3ad in an active/standby redundancy mode, so the standby takes over immediately if the active link(s)fails. The dual-homed access device operates as if it is connected to a single virtual device. MC- LAG is usually enabled on the provider edge (PE) device.Cisco Router 7600 Series Routers and the Cisco ASR9000 Series Aggregation Services Routers support this feature. With MC-LAG, the two routers function as Point of Attachment (POA) nodes and run an Inter-Chassis Communication Protocol (ICCP) to synchronize state and to form a Redundancy Group (RG). Each device controls the state of its MC-LAG peer for a particular link-bundle; one POA is active for a bundle of links while the other POA is a standby. Multiple active link bundles per chassis are supported11.MC-LAG can work in conjunction with L2VPN such as VPLS, but other network transport services such as EoMPLS, L3VPN or QoS can be leveraged as well.

    A use case in the context of DCI LAN extension is that at the edge of a provider’s network, each customer edge (CE) device supporting LACP is dual-homed to two provider edge (PE) devices and distributes the load on a VLAN-based hashing mechanism onto multiple link bundles. Then the MC-LAG device bridges and extends the concerned VLANs over an MPLS core using a VPLS Pseudowire. The MEC function can be enabled on the aggregation layer to improve Layer 2 multipathing intra-data center, so all Layer 2 uplinks from the access layer to the aggregation layers are forwarded.

    MC-LAG offers rapid recovery times in case of a link or node failure, while VPLS addresses the traditional fast convergence, fast reroute and path diversity features supported by MPLS.

    MEC and MC-LAG Function


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