IETF RFC 5786 PDF

Introduction

Motivation

In some cases, it is desirable to set up constrained shortest path first (CSPF) computed Multiprotocol Label Switching (MPLS) Traffic Engineered Label Switched Paths (TE LSPs) to local addresses of a router that are not currently advertised in the TE LSAs, i.e., loopback and non-TE interface addresses.

For instance, in a network carrying VPN and non-VPN traffic, it is often desirable to use different MPLS TE LSPs for the VPN traffic and the non-VPN traffic. In this case, one loopback address may be used as the BGP next-hop for VPN traffic while another may be used as the BGP next-hop for non-VPN traffic. It is also possible that different BGP sessions are used for VPN and non-VPN services. Hence, two separate MPLS TE LSPs are desirable -- one to each loopback address.

However, current routers in an OSPF network can only use CSPF to compute MPLS TE LSPs to the router ID or the local addresses of a remote router's TE-enabled links. This restriction arises because OSPF TE extensions [RFC3630, RFC5329] only advertise the router ID and the local addresses of TE-enabled links of a given router. Other routers in the network can populate their traffic engineering database (TED) with these local addresses belonging to the advertising router. However, they cannot populate the TED with the advertising router's other local addresses, i.e., loopback and non-TE interface addresses. OSPFv2 stub links in the router LSA [RFC2328] provide stub reachability information to the router but are not sufficient to learn all the local addresses of a router. In particular for a subnetted point-to-point (P2P) interface the stub, link ID is the subnet address. While for a non-subnetted interface, the stub link ID is the neighbor address. Intra-prefix LSAs in OSPFv3 [RFC5340] are also not sufficient to learn the local addresses.

For the above reasons, this document defines an enhancement to OSPF TE extensions to advertise the local addresses of a node.