Cabletron Systems SSR-ATM29-02, Руководство пользователя, Страница: 126 / 386

Chapter 9: Configuring Unicast Routing on the SSR
126 CoreWatch User’s Guide
the SSR's subnetwork. You could also configure the SSR to not accept RIP data from the
subnetwork but to accept RIP packets from the other RIP router.
In the IP environment, RIP bases routing on a hop count. RIP only supports routes that
have 0 to 15 hops. You can configure the SSR to adjust hop counts. Doing so lets you
control which routes the SSR prefers to use to send or receive data when it is
communicating with another RIP router.
What Is Preference?
Preference is the value the SSR uses to determine the preference of routes from one
protocol or peer over another. You can set preference based on one network interface over
another, from one protocol over another, or from one remote gateway over another. A
default preference is assigned to each source from which the SSR receives routes.
Preference values range from 0 to 255 with the lowest number indicating the most
preferred route.
Preference may not be used to control the selection of routes within RIP or another
Interior Gateway Protocol (IGP) because that is accomplished automatically by the
protocol’s metric.
Preference may be used to select routes from an Exterior Gateway Protocol (EGP), such as
the Border Gateway Protocol (BGP), learned from different peers or autonomous systems.
As shown in the following table you can set preference in several places. The table
identifies each item on which you can set preference and identifies the default preference
value of each item. For details on setting the preference of static routes, see
“Defining
Static Route Entries” on page 123 . For details on setting the preference of RIP routes, see
“Setting RIP Global Parameters” on page 127 . For details on setting the preference of all
other items, see the SmartSwitch Router Command Line Interface Reference Manual.
Table 14. Preferences and Their Defaults
Preference Default
Directly connected networks 0
Open Shortest Path First (OSPF) routes 10
Static routes 60
RIP routes 100
Point-to-point interfaces 110
Routes to interfaces that are down 120