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Configuring an OSPF Domain ID

For most OSPF configurations involving Layer 3 VPNs, you do not need to configure an OSPF domain ID. However, for a Layer 3 VPN connecting multiple OSPF domains, configuring OSPF domain IDs can help you control LSA translation (for Type 3 and Type 5 LSAs) between the OSPF domains and back-door paths. Each VPN routing and forwarding (VRF) table in a PE router associated with an OSPF instance is configured with the same OSPF domain ID. The default OSPF domain ID is the null value 0.0.0.0. As shown in Table 7, a route with a null domain ID is handled differently from a route without any domain ID at all.

Table 7: How a PE Router Redistributes and Advertises Routes

Route Received	Domain ID of the Route Received	Domain ID on the Receiving Router	Route Redistributed and Advertised As
Type 3 route	A.B.C.D	A.B.C.D	Type 3 LSA
Type 3 route	A.B.C.D	E.F.G.H	Type 5 LSA
Type 3 route	0.0.0.0	0.0.0.0	Type 3 LSA
Type 3 route	Null	0.0.0.0	Type 3 LSA
Type 3 route	Null	Null	Type 3 LSA
Type 3 route	0.0.0.0	Null	Type 3 LSA
Type 3 route	A.B.C.D	Null	Type 5 LSA
Type 3 route	Null	A.B.C.D	Type 5 LSA
Type 5 route	Not applicable	Not applicable	Type 5 LSA

You can configure an OSPF domain ID for both version 2 and version 3 of OSPF. The only difference in the configuration is that you include statements at the [edit routing-instances routing-instance-name protocols ospf] hierarchy level for OSPF version 2 and at the [edit routing-instances routing-instance-name protocols ospf3] hierarchy level for OSPF version 3. The configuration descriptions that follow present the OSPF version 2 statement only. However, the substatements are also valid for OSPF version 3.

To configure an OSPF domain ID, include the domain-id statement:




domain-id domain-Id;

You can include this statement at the following hierarchy levels:

[edit routing-instances routing-instance-name protocols ospf]
[edit logical-systems logical-system-name routing-instances routing-instance-name protocols ospf]

You can set a VPN tag for the OSPF external routes generated by the PE router to prevent looping. By default, this tag is automatically calculated and needs no configuration. However, you can configure the domain VPN tag for Type 5 LSAs explicitly by including the domain-vpn-tag number statement:




domain-vpn-tag number;

You can include this statement at the following hierarchy levels:

[edit routing-instances routing-instance-name protocols ospf]
[edit logical-systems logical-system-name routing-instances routing-instance-name protocols ospf]

The range is 1 through 4,294,967,295 (232 - 1). If you set VPN tags manually, you must set the same value for all PE routers in the VPN.

For an example of this type of configuration, see Configuring an OSPF Domain ID for a Layer 3 VPN.

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