Руководство Пользователя для Netopia 3220-h
Cayman 3220-H User’s Guide
How Your Cayman 3220-H Works
December 2000
C-11
network. When the router receives a packet, it consults its routing
table to decide where to send the packet.
table to decide where to send the packet.
Static and Dynamic
Routes
Routes
Routes to other networks can be entered and maintained manually
(static routes) or acquired from other routers interactively (dynamic
routes):
(static routes) or acquired from other routers interactively (dynamic
routes):
Static routes identify pathways to destination networks that are
stable over time or to networks that must always be available,
even if a link is not currently open. These static routes let each
router recognize how to reach the other, even if one router
hasn't heard from the other recently. Static routes are usually
required for a PPP link to be established “on demand,” since,
without it, the router does not know which interface to route a
packet over to reach the remote network.
stable over time or to networks that must always be available,
even if a link is not currently open. These static routes let each
router recognize how to reach the other, even if one router
hasn't heard from the other recently. Static routes are usually
required for a PPP link to be established “on demand,” since,
without it, the router does not know which interface to route a
packet over to reach the remote network.
Dynamic routes identify pathways to destination networks that
may change over time. Dynamic routes are created and
configured when routers broadcast RIP (Routing Information
Protocol) packets advertising the networks they can reach and
the distance (number of routers) to each network.
may change over time. Dynamic routes are created and
configured when routers broadcast RIP (Routing Information
Protocol) packets advertising the networks they can reach and
the distance (number of routers) to each network.
Selecting the Most
Efficient Route
Efficient Route
The efficiency of a route is expressed in terms of the route's metric,
or hop count, which measures the number of routers a packet must
pass through to reach its destination. A route to a network connected
directly to the router has a metric of 1, a route to a network
reachable through one other gateway has a metric of 2, and so on.
Routes with metrics greater than 16 are considered unreachable and
are discarded.
or hop count, which measures the number of routers a packet must
pass through to reach its destination. A route to a network connected
directly to the router has a metric of 1, a route to a network
reachable through one other gateway has a metric of 2, and so on.
Routes with metrics greater than 16 are considered unreachable and
are discarded.
The PPP interface tries to use the most efficient path to reach a
remote destination network. When only one route (static or
dynamic) to a remote network is available, the router uses that route
to reach the network. When more than one route to a network is
available (for example, when the router has one route to a network
but learns of another one from a new router), the router selects the
more efficient route (that is, the one with the lower metric, or hop
count) and discards the less-efficient one.
remote destination network. When only one route (static or
dynamic) to a remote network is available, the router uses that route
to reach the network. When more than one route to a network is
available (for example, when the router has one route to a network
but learns of another one from a new router), the router selects the
more efficient route (that is, the one with the lower metric, or hop
count) and discards the less-efficient one.