Compatible Systems 5.4 - Manual (Page 47)

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.