Next-Hop Address And Forwarding Interface; Administrative Distance And Metric - HP ProCurve 7000dl Series Basic Management And Configuration Manual

IP Routing—Configuring Static Routes
Overview
11-8

Next-Hop Address and Forwarding Interface

A route's next-hop address and forwarding interface instruct the router how
to forward packets that match the destination address for the route.
The next-hop address is the address of the next directly-connected device en
route to the destination address. The router determines the forwarding
interface for the route by looking up, in its routing table, the interface that
connects to the next-hop address. (Because the next-hop address should be
a directly connected device, the routing table will automatically include this
information.)
Only a forwarding interface is absolutely necessary for a route. When you add
a static route to the routing table, you can specify a forwarding interface
instead of a next-hop address. The next-hop address is then listed as 0.0.0.0.

Administrative Distance and Metric

A router may learn more than one route to the same destination. The router
compares the administrative distances and metrics of identical routes to
select the single best route that it will add to its routing table. (You can also
enable the router to select more than one best route. See "Load Sharing" on
page 11-11.)
The ProCurve Secure Router uses administrative distance to compare routes
learned by different routing protocols or methods. The ProCurve Secure Router
uses metrics to compare routes learned by the same routing protocol. That is,
each routing protocol used on a router has its own database of routes. When a
routing protocol knows more than one route to a destination, it selects the route
with the lowest metric as its best route. The router then compares the best
routes of each method and selects the route with the lowest administrative
distance.
A route's administrative distance indicates how reliable the router considers
the method through which it discovered the route. The lower the administrative
distance the more trustworthy the route.
If you are only using static routes, you generally do not need to worry about
administrative distance. However, if you are using static routing in conjunc-
tion with a routing protocol, you should understand how the ProCurve Secure
Router uses administrative distance to choose between identical routes
learned using different methods. The ProCurve Secure Router always selects
the route with the lower administrative distance. For example, statically
configured routes have a default administrative distance of 1, while Routing
Information Protocol (RIP) routes have a default administrative distance of
120. When the router knows an identical RIP and static route, it only adds the
static route to the routing table.