Compatible Systems 5.4 manual Ospf

Chapter 2 - IP Routing & Bridging 41

smaller routers can be set to use one of these backbone routers as their default router.

RIP Split Horizon

Normally, RIP uses a technique called split horizon to avoid routing loops and allow smaller update packets. This technique specifies that when the router sends a RIP update out a particular network interface (including a Bridge Group logical interface made up of multiple physical member interfaces), it should never include routing information acquired over that same interface.

There is a variation of the split horizon technique called “poison reverse” which specifies that all routes should be included in an update out a particular interface, but that the metric should be set to infinity for those routes acquired over that interface. One drawback is that routing update packet sizes will be increased when using poison reverse.

•If Split Horizon is selected with this pull-down menu, the router will apply the split horizon technique to routes being output over this Bridge Group’s member interfaces.

•If No Split Horizon is selected with this pull-down menu, the router will include all routes in output packets sent over this Bridge Group’s member interfaces, regardless of which interface they were acquired over, and will use a normal metric.

•If Poison Reverse is selected with this pull-down menu, the router will include all routes in an output packet sent over this Bridge Group’s member interfaces, but will set the metric to infinity for those routes which were acquired over these interfaces.

Directed Broadcast

This checkbox sets whether the interface will forward network-prefix-directed broadcasts. This is a security feature which can help prevent your network from being used as an intermediary in certain kinds of attacks which use ICMP echo traffic (pings) or UDP echo packets with fake (i.e., “spoofed”) source addresses to inundate a victim with erroneous traffic.

Options

The options button brings up the Bridge-TCP/IP Routing Options Dialog Box which provides access to Proxy ARP, UDP Relays and other configuration information. This dialog box is discussed later in this chapter.

OSPF

This option button brings up the OSPF Dialog Box which allows the OSPF routing protocol to be enabled. For more information on this dialog box and other OSPF parameters, refer to Chapter 15 - OSPF.