In z/OS Communications Server what is the function of router advertisements?

For IPv6-enabled installations only, router advertisements are used to implement router discovery, one of the functions of the IPv6 neighbor discovery protocol.

Router advertisements are sent by routers to announce their availability. z/OS Communications Server receives router advertisements, but it does not originate them. The router advertisement includes information that is used by z/OS Communications Server, including an indication of whether the sending router should be used as a default router.

The IP Configuration Guide points out: "All that is needed is at least one IPv6 interface that is defined and started, and at least one adjacent router through that interface that is configured for IPv6 router discovery. If these things exist, then z/OS Communications Server begins receiving router advertisements."

Router advertisements are sent out as ICMPv6 packets.

If an adjacent router is advertising itself as a default router using both IPv6 OSPF or IPv6 RIP and router discovery, the default routes learned from IPv6 OSPF or IPv6 RIP take precedence and generate the default routes in the TCPIP stack's IPv6 route table. Any default routes learned from router discovery are ignored as long as the default routes learned from IPv6 OSPF or IPv6 RIP exist.