UNIX System Administration Handbook - Evi Nemeth [220]
The configuration on the next page is for an environment in which both RIP and OSPF are in use. The configuration is for the area-border router shown in Exhibit C (also on the next page).
Exhibit C Network topology for our sample gated configuration
The upstream network (the corporate backbone) has standardized on OSPF, but the downstream LAN has devices (a few network printers) that can only listen to RIP. In this environment, gated is used to rebroadcast the OSPF routes via RIP. This is a good configuration for a corporate or campus environment because it lets PCs and network appliances learn information via RIP, yet uses a more sensible protocol to communicate on the backbone among groups, floors, and buildings.
The contents of the configuration file are as follows:
Section 1: rip yes {
broadcast;
defaultmetric 10;
interface 192.225.40.253 noripout;
interface 192.225.55.253 ripout;
} ;
Section 2: ospf yes {
area 0.0.0.2 {
authtype none;
networks {
192.225.55.0 mask 255.255.255.0;
};
interface 192.225.55.253 cost 1 {
priority 2;
};
};
backbone {
interface 192.225.40.253 {
priority 2;
};
};
};
Section 3: static {
default gateway 192.225.40.254 preference 140 retain;
};
Section 4: export proto rip {
proto ospf {
ALL metric 1;
};
proto direct {
ALL metric 1;
};
proto static {
ALL metric 1;
};
};
Section 5: export proto ospf {
proto direct {
ALL metric 1;
};
};
In section 1, gated is instructed to speak the RIP protocol. It listens for RIP broadcasts from other routers on both interfaces but sends out RIP packets of its own only on the 192.225.55.253 interface. This restriction serves to eliminate undesirable broadcast traffic on the corporate backbone.
Section 2 enables OSPF. The 192.225.40.253 interface is in area 0, the backbone area. It will send out OSPF HELLO messages to other routers on this network to discover who its neighbors are. 192.225.55.253 is in area 2. (There may or may not be other downstream routers that want to share information via OSPF.)
Currently, there is only one way out of this network to the outside world. Hence, for good measure, section 3 includes a static default route to the Internet gateway on the 192.225.40.0 network.
In sections 4 and 5, we tell gated what routes to advertise via RIP and OSPF, respectively. We want the RIP advertisements to include any directly connected networks, the static default route, and any routes learned via OSPF. We want the OSPF advertisements to include any directly connected networks (such as the 192.225.55.0 network). Since we are an interior router, we do not want to announce a default route.
14.6 VENDOR SPECIFICS
gated is not shipped with the Solaris distribution. routed is turned on in chatty mode if the host has two or more (real) network interfaces and does not use DHCP. If either of these conditions is not met, routed is turned on in quiet (-q) mode if a default route is not set (in /etc/defaultrouter) and the Router Discovery Protocol (the in.rdisc daemon) isn’t in use. Whew.
gated is started if GATED=1 is asserted in /etc/rc.config.d/netconf. routed is not shipped with the HP-UX distribution.
On Red Hat systems, gated is started if the file /etc/gated.conf exists. routed is disabled by default; to enable it, rename the startup file /etc/rc.d/rc3.d/K55routed to S55routed (you can also do this with the graphical interface, control-panel).
FreeBSD starts routed at boot time if router_enable is set to YES and router is set to routed in rc.conf. In order for a FreeBSD box to perform packet forwarding among interfaces, gateway_enable must also be set to YES in rc.conf. You can install gated from the /usr/ports/gated directory.
14.7 ROUTING STRATEGY SELECTION CRITERIA
There are essentially four levels of complexity at which the routing for a network can be managed:
• No routing
• Static routes only
• Mostly static routes, but clients listen for RIP updates
• Dynamic routing everywhere
The topology of the overall network has a dramatic