Layer 3 Vpn Application - Cisco Catalyst 3750 Software Configuration Manual

Metro switch

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Layer 3 VPN Application

Layer 3 VPN services can use multi-VRF-CE or MPLS VPNs to deploy and administer scalable Layer 3

VPN services to business customers. A Layer 3 VPN is a secure IP-based network that shares resources

on one or more physical networks. It contains geographically dispersed sites that can communicate

securely over a shared backbone.

Catalyst 3750 Metro switches or other Layer 3 switches) use a routing protocol, such as RIP, EBGP,

OSPF, IS-IS, or static routing, to forward packets from customer VPNs to the Catalyst 3750 Metro PE

devices at the edge of the MPLS network. The PE device is configured with multiprotocol BGP

(MP-BGP), and a route distinguisher that is associated with the customer's VPN. The PE device converts

this information to a VPN-IPv4 format and adds layer distribution protocol (LDP) labels to establish

VPN routes are distributed over the MPLS network using MP-BGP, which also distributes the labels

associated with each VPN route. MPLS VPN depends on VPN routing and forwarding (VRF) support to

isolate the routing domains from each other.

When an MPLS-VPN packet is received on a port, the CE switch looks up the labels in the routing table

to determine what to do with the packet. A PE router binds a label to each customer prefix learned from

a CE device and includes the label in the prefix that it advertises to other PE routers. When a PE router

forwards a packet across the provider network, it labels the packet with the label learned from the

destination PE router. When the destination PE router receives the labeled packet, it examines the label

and uses it to direct the packet to the correct CE device.

Only the PE routers at each end of the MPLS network maintain the VPN routes for VPN members.

Provider routers in the core network do not maintain the VPN routes. This ensures the security of

customer VPNs and isolates them from other customer packets that are carried across the

service-provider MPLS network.

illustrates a typical MPLS VPN configuration. The CE devices (which can be

MPLS VPN Configuration

PE-CE routing protocol

static, RIPv2, EBGP, OSPF

CE = Customer edge switch

P = Provider router

PE = Provider edge switch (Catalyst 3750 Metro switch)

Catalyst 3750 Metro Switch Software Configuration Guide

Network Configuration Examples