Configuring a router

An internal router is normally configured to advertise routes by running the routed routing daemon.

A router must be configured to forward packets. You can use the Network Configuration Manager to configure a machine as a router. Alternatively, you can use the inconfig(1Mtcp) command to do this:

1. Set the values of the ipforwarding and ipsendredirects kernel variables to 1 by entering the following commands:
   
   inconfig ipforwarding 1
   inconfig ipsendredirects 1

   If ipforwarding is turned on, the router will forward packets that it receives on one network interface to a destination that is reachable through another of its network interfaces.

   If ipsendredirects is turned on, and the router forwards an incoming packet to another router out of the same interface on which it received the packet, it will send an Internet Control Message Protocol (ICMP) redirect error to the originator of the packet. The ICMP redirect updates the routing table of the originating host with information about the router that it should be using. In this way, hosts that are configured with a single default router can gradually learn about other routers.

2. For security reasons, some sites prefer not to allow routers to forward source-routed datagrams that are not destined for local networks.

   If you do not want the router to forward source-routed datagrams, enter:
   
   inconfig ipnonlocalsrcroute 0

   If you want the router to forward source-routed datagrams, enter:
   
   inconfig ipnonlocalsrcroute 1

3. Determine the routing protocols to be used to communicate with other machines based on whether the host is a router and the complexity of the network topology:

   • For a router on a simple network, run routed to implement Version 1 of the RIP protocol. If desired, you can disable the RIP Version 2 and Internet router discovery (IRD) capabilities of routed using appropriate entries in the /etc/inet/gateways file.

   • For a router on a complex network, run routed to implement RIP Version 2, or gated to implement RIP Version 2 and/or OSPF. RIP Version 2 has the advantage over Version 1 of allowing a router to advertise a next hop through a router other than itself.

     Either routed or gated can be used to implement version 2 of the RIP protocol.

     If you need also to use any of the OSPF, EGP, or BGP protocols in conjunction with RIP, you must use gated to implement RIP.

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     NOTE: Do not run routed and gated together on the same machine; they are exclusive of each other.

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   • It is also possible not to run a routing daemon at all on a router and, instead, configure static routes in the router's routing table. This is not recommended as the router will not advertise its routes and it will need to be manually reconfigured each time the network topology changes.

4. Configure the system for the routing daemons selected:

   • To configure routed, see ``Configuring routed on a router''.

   • To configure gated, see ``Configuring gated on a router''.

   • To configure static routes, see ``Specifying routers''.