When OMPROUTE is initialized, it uses the OMPROUTE configuration file to determine which routing protocols will be enabled. If at least one OSPF interface is configured, the OSPF protocol is enabled. If at least one RIP interface is configured, RIP is enabled. If at least one IPv6 RIP interface is configured, IPv6 RIP is enabled. If at least one IPv6 OSPF interface is configured, IPv6 OSPF is enabled. If OMPROUTE is started with no interfaces defined for a particular protocol, that protocol is disabled until one of the following events occur:
When OMPROUTE is configured for both the OSPF and RIP protocols (either IPv4 or IPv6), routes that are learned through the OSPF protocol take precedence over routes learned through the RIP protocol.
The OSPF and RIP protocols are communicated over IPv4 interfaces that are defined with the OSPF_INTERFACE and RIP_INTERFACE configuration statements, respectively. An IPv4 interface involved in the communication of neither the RIP nor the OSPF protocol should be configured to OMPROUTE with the INTERFACE configuration statement, unless Ignore_Undefined_Interfaces=YES is coded on the Global_Options configuration statement. OMPROUTE supports a maximum of 255 real, physical, IPv4 interfaces (that is, interfaces on which data can actually be sent and received). There is no theoretical limit on how many VIPAs can be configured, though there are practical limits imposed by network design. For special VIPA considerations, see step 5.
The IPv6 OSPF and IPv6 RIP protocols are communicated over IPv6 interfaces that are defined with the IPV6_OSPF_INTERFACE and IPV6_RIP_INTERFACE configuration statements, respectively. An IPv6 interface not involved in the communication of the IPv6 OSPF or IPv6 RIP protocol can be configured to OMPROUTE with the IPV6_INTERFACE configuration statement. If default values are acceptable and you do not need to define additional prefixes to an IPv6 interface not involved in the communication of the IPv6 OSPF or IPv6 RIP protocol, it is not necessary to configure the interface to OMPROUTE at all. OMPROUTE will learn about the interface and its MTU value from the stack and use default values for other parameters. This is different from IPv4, where all interfaces should be configured to prevent OMPROUTE from using default values for MTU size and subnet mask, unless Global_Options is coded with Ignore_Undefined_Interfaces=YES.
OMPROUTE allows for the generation of multiple, equal-cost routes to a destination. For OSPF and IPv6 OSPF, up to 16 multiple equal-cost routes are allowed. For RIP and IPv6 RIP, multiple equal-cost routes are supported only to directly connected destinations over redundant interfaces.