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Increased number of OSPF processes in MPLS VPN environments

When we were writing the MPLS and VPN architectures books, there was a limit on the number of OSPF processes you could configure per PE-router. The limit was based on the fact that IOS supports up to 32 sources of routing information; two of them are static and connected plus you need an IGP and BGP in the MPLS VPN backbone, resulting in 28 OSPF processes that could be configured on a single PE-router. This "feature" severely limited OSPF-based MPLS VPN deployments until IOS release 12.3(4)T when the limitation was removed, resulting in availability of up to 30 routing processes per VRF.

RIP, BGP and EIGRP never experienced the same limitations as you configure VRF-specific routing instances within address families of a single routing protocol

The details of the actual change that took place are not obvious from the IOS documentation; they simply changed the global allocation of routing process identifiers to per-routing-table identifiers. For example, in the following show ip protocol summary printouts, the two OSPF processes (one in global routing table, one in VRF test) share the same index.

router#show ip protocols summary
Index Process Name
0 connected
1 static
2 ospf 112
router#show ip protocols vrf Test summary
Index Process Name
0 connected
1 static
2 ospf 111

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