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When BGP next-hop neighbor discovery is enabled, a database of BGP next-hop neighbors in use by any
VRF associated with the source PE router is generated, based on information from the local VRF and global
routing tables. As routing updates are received, new BGP next-hop neighbors are added immediately to the
database. However, BGP next-hop neighbors that are no longer valid are removed from the database only
periodically, as defined by the user.
Figure 6: BGP Next-hop Neighbor Discovery for a Simple VPN, on page 207
shows how BGP next-hop
neighbor discovery works for a simple VPN scenario for an Internet service provider (ISP). In this example,
there are three VPNs associated with router PE1: red, blue, and green. From the perspective of router PE1,
these VPNs are reachable remotely through BGP next-hop neighbors PE2 (router ID: 12.12.12.12) and PE3
(router ID: 13.13.13.13). When the BGP next-hop neighbor discovery process is enabled on router PE1, a
database is generated based on the local VRF and global routing tables. The database in this example contains
two BGP next-hop router entries, PE2 12.12.12.12 and PE3 13.13.13.13. The routing entries are maintained
per next-hop router to distinguish which next-hop routers belong within which particular VRF. For each
next-hop router entry, the IPv4 Forward Equivalence Class (FEC) of the BGP next-hop router in the global
routing table is provided so that it can be used by the MPLS LSP ping operation.
Figure 6: BGP Next-hop Neighbor Discovery for a Simple VPN
IP SLA LSP Ping and LSP Traceroute Operations
This feature introduces support for the IP SLA LSP ping and IP SLA LSP traceroute operations. These
operations are useful for troubleshooting network connectivity issues and determining network availability
in an MPLS VPN. When using MPLS LSP monitoring, IP SLA LSP ping and LSP traceroute operations are
automatically created to measure network connectivity between the source PE router and the discovered
destination PE routers. Individual IP SLA LSP ping and LSP traceroute operations can also be manually
configured. Manual configuration of these operations can be useful for troubleshooting a connectivity issue.
For more information about how to configure IP SLA LSP ping or LSP traceroute operations using MPLS
LSP monitoring, see the
Configuring an MPLS LSP Monitoring Ping Instance, on page 265
and the
an MPLS LSP Monitoring Trace Instance, on page 269
.
Cisco ASR 9000 Series Aggregation Services Router System Monitoring Configuration Guide, Release 4.2.x
207
Implementing IP Service Level Agreements
MPLS LSP Monitoring