Руководство Пользователя для Netopia 2e-h-w
Cayman 2E-H-W User’s Guide
How Your Cayman 2E-H-W Works
November 2000
C-11
Selecting the Most 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.
If the router has a static route and a dynamic route with the same
metric, it uses the static route and discards the dynamic route. If a
router has one dynamic route to a remote network but learns of
another with the same metric, it retains the existing route and
discards the new route.
metric, it uses the static route and discards the dynamic route. If a
router has one dynamic route to a remote network but learns of
another with the same metric, it retains the existing route and
discards the new route.
NOTE: Under some circumstances, you may want your router to use
the same path consistently to reach a remote network, even if
another, more efficient route to the remote network exists. To
accomplish this, set up a static route for the preferred pathway and
assign it a metric of 1 (even if the actual destination to that network
is more than 1). This will ensure the route cannot be replaced by a
dynamic route.
the same path consistently to reach a remote network, even if
another, more efficient route to the remote network exists. To
accomplish this, set up a static route for the preferred pathway and
assign it a metric of 1 (even if the actual destination to that network
is more than 1). This will ensure the route cannot be replaced by a
dynamic route.
Dealing with Unavailable Routes
A router acquiring dynamic routes from other gateways needs to be
able to identify routes that are no longer available. A router considers
a route unavailable when the route times out or a PPP link goes
down:
able to identify routes that are no longer available. A router considers
a route unavailable when the route times out or a PPP link goes
down: