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DES-7200 Configuration Guide Chapter 2 Configuring BGP IP VPN
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2.3.5 Configure OSPF VPN extension
2.3.5.1 Introduction to L3VPN OSPF VPN
extension
PE-CE OSPF feature
OSPF is widely applied IGP protocol. In most of the existing application scenarios, VPN user
generally selects OSPF as the interior routing protocol. If OSPF protocol is deployed between
PE and CE, you won't have to run other routing protocols again, thus simplifying CE
configuration and management.
PE-CE OSPF feature will be introduced from the following four aspects.
Domain ID
Domain ID refers to the OSPF domain to which the route belongs. When CE has learned an
OSPF route from interior site of VPN, this route will be advertised to PE in type-1, type-2 or
type-3 LSAs and redistributed to BGP to form VPN route. Meanwhile, the domain ID will also be
redistributed to BGP together with the route and advertised as the Extended Communities
attribute in the VPN route. When other PEs receive this VPN route and redistribute to the VRF
OSPF instance, the domain ID will also be redistributed to the corresponding VRF OSPF
instance together with this route. If VRF OSPF instance confirms that domain ID contained in the
route is same as the domain ID of this VRF OSPF instance, then the route will be advertised to
CE as an internal route. Contrarily, if VRF OSPF instance confirms the domain ID contained in
the route is different from the domain ID of this VRF OSPF instance, then the route will be
advertised to CE as an external route.
As shown below, for a route that belongs to the same OSPF domain, CE1 advertises the route to
PE1 in type-2 LSA and then VPN route is formed and advertised to PE2, which will receive this
route and redistribute to VRF OSPF instance. Since the VRF OSPF instance shares the same
domain ID with this VPN route, this site will eventually be advertised to VPN sites in the form of
internal route.