Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1: Base Functions, Connectivity, and Routing

154 Communications Server for z/OS V1R7 TCP/IP Implementation, Volume 1 - Base Functions, Connectivity, and Routing

򐂰 z/OS CS: IP Configuration Reference, SC31-8776

5.2 Why IP routing is important

IP routing is one of the most important processes that takes place at the network layer. It is

the function that really defines Layer 3 of the OSI Reference Model. Routing is what enables

local networks to be linked to larger networks, virtually allowing a host to communicate with

any host located anywhere. It provides the desired network scalability, while it still can be

managed within its own AS boundaries.

5.3 Using OMPROUTE in a z/OS environment

OMPROUTE is the strategic routing daemon for CS for z/OS. For IPv4, OMPROUTE

implements the OSPF protocol described in RFC 1583 (OSPF version 2), the OSPF

subagent protocol described in RFC 1850 (OSPF version 2 Management Information Base),

and the RIP protocols described in RFC 1058 (Routing Information Protocol) and in RFC

1723 (RIP version 2 - Carrying Additional Information).

For IPv6, OMPROUTE implements the IPv6 RIP protocol described in RFC 2080 (RIPng for

IPv6) and the IPv6 OSPF protocol described in RFC 2740 (OSPF for IPv6).

It provides an alternative to the static TCP/IP gateway definitions. The z/OS host running with

OMPROUTE becomes an active OSPF or RIP router in a TCP/IP network. Either or both of

these routing protocols can be used to dynamically maintain the host IPv6 routing table.

5.3.1 Overview

OMPROUTE manages a TCP/IP stack’s routing table. It is not involved in any decisions

made by the stack when routing a packet to its destination.

During initialization OMPROUTE deletes all dynamic routes from the TCP/IP stack’s routing

table. OMPROUTE then repopulates the stack routing table using information learned via the

routing protocols.

OMPROUTE does not make use of the BSDROUTINGPARMS statement. Instead, its

parameters are defined in the OMPROUTE configuration file. The OMPROUTE configuration

file is used to define both OSPF and RIP environments.

The OSPF and RIP protocols are communicated over interfaces defined with the

OSPF_INTERFACE and RIP_INTERFACE configuration statements. Interfaces that are not

involved in the communication of the RIP or OSPF protocol are configured to OMPROUTE

via the INTERFACE configuration statement (unless it is a non-point-to-point interface and all

default values specified on the INTERFACE statement are acceptable).

A one-to-one relationship exists between an OMPROUTE and a TCP/IP stack. OSPF/RIP

support for multiple TCP/IP stacks requires multiple instances of OMPROUTE.

In an OMPROUTE environment, OSPF takes precedence over RIP and other routing

protocols. If both OSPF and RIP protocols are used, OSPF routes will be preferred over RIP

routes to the same destination.

OMPROUTE allows the generation of multiple, equal-cost routes to a destination, thus

providing load-balancing support.