3Com CoreBuilder 3500, Руководство по внедрению

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Key Concepts 273
Routing table data is updated statically or dynamically:
■
Statically
— You manually enter static routes in the routing table.
Static routes are useful in environments where no routing protocol is
used or where you want to override some of the routes that are
generated with a routing protocol. Because static routes do not
automatically change in response to network topology changes,
manually configure only a small number of reasonably stable routes.
Static routes do not time out, but they can be learned.
■
Dynamically — Routers use a protocol such as RIP or OSPF to
automatically exchange routing data and to configure their routing
tables dynamically. Routes are recalculated at regular intervals. This
process helps you to keep up with network changes and allows the
system to reconfigure routes quickly and reliably. Interior Gateway
Protocols (IGPs), which operate within networks, provide this
automated method.
Default Route
In addition to the routes to specific destinations, a routing table can
contain a
default route
. The router uses the default route to forward
packets that do not match any other routing table entry.
A default route is often used in place of static routes to numerous
destinations that all have the same gateway IP address and interface
number. The default route can be configured statically, or it can be
learned dynamically.
A drawback to implementing a default static route is that it is a single
point of failure on the network. You can implement Virtual Router
Redundancy Protocol (VRRP) on your network to remedy this problem.
For more information about VRRP, see Chapter 12.