Use of static routing with OMPROUTE

Do not use non-replaceable static routes with OMPROUTE because those routes cannot be dynamically updated in response to network topology changes. An exception is when routes must be defined to destinations that, for some reason, cannot be learned dynamically through the routing protocol. Start of change Use the BEGINROUTES statement in PROFILE.TCPIP to define IPv4 or IPv6 static routes if they are required. End of change

TCP/IP treats static routes that are defined as replaceable on the BEGINROUTES statement as last-resort routes. If a dynamic route is learned for the destination that was specified in a replaceable static route, the dynamic route replaces the static route in the route table. Additionally, if a replaceable static route is replaced with a dynamic route, TCP/IP always retains knowledge of the replaceable static route and reinstalls it if the destination becomes unreachable using dynamic routes. TCP/IP does not relearn replaceable static routes that were replaced. For this reason, replaceable static routes can be used with OMPROUTE as backup routes to use if nothing is found dynamically.

Another situation in which static routes might be required is when multiple, equal-cost routes to a destination are needed and the RIP or IPv6 RIP routing protocol is used. Static routes might be required in this case because, except for directly attached resources, the RIP and IPv6 RIP protocols do not create multiple, equal-cost routes to a destination. In other words, if multiple adjacent routers are advertising through RIP or IPv6 RIP that they can reach the same destination, OMPROUTE adds a route to the TCP/IP route table through only one of those adjacent routers. If more than one of these routes must exist, they must be statically configured in PROFILE.TCPIP by using the BEGINROUTES statement. For example, in Figure 1, this configuration would be necessary if you wanted host TCPCS4 to have two routes to the IPv6 prefix 2001:DB8:0:A10::/60 (one through router A and one through router B).

If a TCP/IP stack has multiple interfaces to a directly attached network and you want to use one interface for input packets and one for output packets (traffic splitting), you can use static routes. To use traffic splitting, you can define a static route for only one interface, forcing all output packets to use that interface. The other routers on the directly attached network must be defined with a similar static route, but for the other interface. Although this method is the easiest way to implement traffic splitting, if one of the interfaces fails, a host might become unreachable even though the other interface remains active.

Tip: A more robust way of accomplishing traffic splitting is to use dynamic routes and make one route preferred over the other through the configured interface costs. For more information, see step 7.

The BSDROUTINGPARMS statement in PROFILE.TCPIP is not used when the OMPROUTE routing daemon is used. Instead, the IPv4 interface characteristics, including subnet mask, are defined in the OMPROUTE configuration file.