Multicast and Routing Guide K/KA/KB.15.15

NOTE: OSPF is automatically enabled without a system reset.
General configuration steps for OSPF
To begin using OSPF on the routing switch:
1. In the global config context, use ip routing to enable routing (page “Enabling IP routing”
(page 140).)
2. Execute router ospf to place the routing switch in the ospf context and to enable OSPF
routing (page A-21.)
3. Change theOSPF RFC 1583 compliance, if needed. (See “Changing the RFC 1583 OSPF
compliance setting” (page 141).)
4. Use area to assign the areas to which the routing switch will be attached (page A-25.)
5. Assign interfaces to the configured areas per-VLAN or per-subnet by moving to each VLAN
context and using one of the following commands:
• ip ospf area ospf-area-id assigns all interfaces in the VLAN to the same area.
Use this option when there is only one IP address configured on the VLAN or you want
all subnets in the VLAN to belong to the same OSPF area.
• ip ospf ip-address area ospf-area-idassigns an individual subnet to the
specified area.
6. Optional: Assign loopback interfaces to OSPF areas by using the ip ospf area command
at the loopback interface configuration level. (See “Assigning loopback addresses to an area”
(page 146).)
7. Optional: On each routing switch used as an ASBR in your OSPF domain, configure
redistribution to enable importing the routes you want to make available in the domain.
a. On an ASBR in a backbone, normal, or NSSA area where you want to import external
routes, configure redistribution filters to define the external routes you do not want
imported.
b. Enable redistribution.
See “Configuring external route redistribution in an OSPF domain (optional)” (page 148).
8. Optional: Configure ranges on ABRs to reduce inter-area route advertising.
9. Optional: Use administrative distance to influence route choices.
10. Optional: Change OSPF trap generation.
11. Optional: Reconfigure default parameters in the interface context, if needed. Includes cost,
dead-interval, hello-interval, priority, and others.
12. Optional: Configure OSPF interface authentication.
13. Configure virtual links for any areas not directly connected to the backbone.
Configuration rules
• If the switch is to operate as an ASBR, you must enable redistribution (step 7 (page 199). When
you do that, ASBR capability is automatically enabled. For this reason, you should first configure
redistribution filters on the ASBR. Otherwise, all possible external routes will be allowed to
flood the domain. (See “Configuring external route redistribution in an OSPF domain (optional)”
(page 148).)
• Each VLAN interface on which you want OSPF to run must be assigned to one of the defined
areas. When a VLAN interface is assigned to an area, the IP address is automatically included
in the assignment. To include additional addresses, you must enable OSPF on them separately,
or use the "all" option in the assignment.
Dynamic OSPF activation and configuration 199