Cisco 10000 - Manual (Page 133)

C H A P T E R
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Cisco 10000 Series Router Software Configuration Guide
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Configuring Multiprotocol Label Switching
Multiprotocol label switching (MPLS) combines the performance and capabilities of Layer 2 (data link
layer) switching with the proven scalability of Layer 3 (network layer) routing. MPLS enables service
providers to meet the challenges of explosive growth in network utilization while providing the
opportunity to differentiate services without sacrificing the existing network infrastructure. The MPLS
architecture is flexible and can be employed in any combination of Layer 2 technologies. MPLS support
is offered for all Layer 3 protocols, and scaling is possible well beyond that typically offered in today's
networks.
This chapter describes the following MPLS-related features:
• BGP Multipath Load Sharing for eBGP and iBGP in an MPLS VPN, page 4-1
• IPv6 VPN over MPLS, page 4-7
• Session Limit Per VRF, page 4-15
• Half-Duplex VRF, page 4-21
For more information about MPLS, see Chapter 3, “Configuring Remote Access to MPLS VPN” and see
the Multiprotocol Label Switching on Cisco Routers, Release 12.1(3)T feature module.
BGP Multipath Load Sharing for eBGP and iBGP in an MPLS VPN
Load sharing is a concept that allows the Cisco 10000 series router to take advantage of multiple best
paths to a given destination. The paths are derived either statically or with dynamic protocols such as
RIP, BGP, OSPF, and IGRP. The best path algorithm decides which is the best path to install in the IP
routing table and to use for forwarding traffic.
The BGP Multipath Load Sharing for eBGP and iBGP in an MPLS VPN feature allows you to configure
multipath load sharing with both external Border Gateway Protocol (eBGP) and internal BGP (iBGP)
paths in BGP networks that are configured to use Multiprotocol Label Switching (MPLS) Virtual Private
Networks (VPNs). BGP Multipath Load Sharing provides improved load sharing deployment and
service offering capabilities and is useful for multihomed autonomous systems and provider edge (PE)
routers that import both eBGP and iBGP paths from multihomed and stub networks.
BGP installs up to the maximum number of paths allowed (configured using the maximum-paths
command). BGP uses the best path algorithm to select one multipath as the best path, insert the best path
into the routing information base (RIB), and advertise the best path to BGP peers. Other multipaths may
be inserted into the RIB, but only one path is selected as the best path.
Note The maximum number of configurable paths on the PRE2 is 6.