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About MPLS Layer-2 VPNs
By mapping to a specific FEC, the MPLS label efficiently provides the router with all of
the local link information needed for immediate forwarding to the next hop. MPLS
creates a Label Switched Path (LSP) along which each Label Switch Router (LSR) can
make forwarding decisions based solely upon the content of the labels. At each hop,
the LSR simply strips off the existing label and applies a new one that tells the next LSR
how to forward the packet.
About MPLS Layer-2 VPNs
As networks grow and become more pervasive, the need to separate the physical
network infrastructure from the logical network or VLAN organization has become
increasingly important. By logically separating the network topology from the service
provided by the physical network, services are more easily managed, reliability through
increased redundancy is improved, and you gain more efficient use of the physical
network infrastructure.
By mapping a VLAN to a specific set of MPLS tunnels, you can create virtual private
networks (VPNs). Within a VPN, all traffic is opaquely transported across the service
provider network. Each VPN can be managed and provisioned independently.
VPNs may have two or more customer points of presence (PoP). All PoPs are
interconnected using point-to-point tunnels. If there are two PoPs in the VPN, the VPN
is considered to be point-to-point. If there are more than two PoPs in the VPN, the VPN
is considered to be multipoint. Multipoint VPNs can be fully-meshed or hub-and-spoke.
Layer-2 VPNs are constructed from a set of interconnected point-to-point MPLS tunnels.
Tunnel endpoint nodes operate as virtual VPN switches, bridging traffic between
tunnels and the local egress VLAN. MAC caching is integrated into the MPLS module.
Source MAC addresses within each VPN are associated with the tunnel from which the
packet is received. Up to 256K MAC addresses can be cached. Within a VPN, once a
MAC address has been learned, unicast traffic destined to the cached MAC address is
transmitted over a single tunnel. Integrated VPN MAC caching enhancement increases
network performance and improves VPN scalability.
MPLS Module Installation and User Guide
1-7
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