Manual Mpls

Cisco − Configuring Basic MPLS Using OSPF

Cisco − Configuring Basic MPLS Using OSPF

Table of Contents
Configuring Basic MPLS Using OSPF.............................................................................................................1Introduction..............................................................................................................................................1 Mechanism........................................................................................................................................1 Hardware and Software Versions......................................................................................................2 Network Diagram.....................................................................................................................................2 Configurations.........................................................................................................................................2 Quick Configuration Guide...............................................................................................................2 ConfigurationFile.............................................................................................................................3 Sample show Output................................................................................................................................4 Related Information.................................................................................................................................6

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Configuring BasicMPLS Using OSPF
Introduction
This sample configuration shows how to set up a Multiprotocol Label Switching (MPLS) network for further tasks such as Virtual Private Network (VPN) or traffic engineering (see these Sample Configurations on the MPLS Support Page for more information).

Mechanism
An MPLS network is commonly a backbone network comprised of MPLS−enabled routers called Label SwitchRouters (LSR). Generally, the network consists of a core LSR with an edge LSR responsible for applying labels to packets. The setup mechanism of an MPLS network is the following: 2. Routing tables of the different LSRs are computed using an Interior Gateway Protocol (IGP). A link−state protocol such as Open Shortest Path First (OSPF) or Intermediate System−to−Intermediate System (IS−IS) is required ifyou're going to deploy MPLS Traffic Engineering. 1. A label distribution protocol (LDP) advertises the bindings between routes and labels. These bindings are checked against the routing table. If the route (prefix/mask and next hop) learned via the LDP matches the route learned via IGP in the routing table, an entry is created in the label forwarding information bases (LFIB) on the LSR. The LSRuses the following forwarding mechanism: 3. Once an edge LSR receives an unlabelled packet, the Cisco Express Forwarding table is checked and a label is imposed on the packet if needed. This LSR is called the ingress LSR. 2. Upon the arrival of a labelled packet at the incoming interface of a core LSR, the LFIB provides the outgoing interface and the new label that will be associated with theoutgoing packet. 1. The router before the last LSR (the penultimate hop) pops the label and transmits the packet without the label. The last hop is called the egress LSR. The following diagram illustrates this network setup:

Cisco − Configuring Basic MPLS Using OSPF

Hardware and Software Versions
This configuration was developed and tested using the software and hardware versions below. • CiscoIOS® Software Releases 12.0(11)S and 12.1(3a)T • Cisco 3600 routers

Network Diagram

Configurations
Quick Configuration Guide
4. Set up your network as usual (MPLS needs a standard IP connection in order to establish forwarding bases). 3. Ensure that the routing protocol (OSPF or IS−IS) is working correctly. These commands are underlined is the configurations below. 2. Enable ip cef (for better...