5
Routing
87
Components of a route
When
a
route
is
defined,
it
consists
of
the
following
properties:
•
Interface
This
is
the
interface
to
forward
the
packet
on
in
order
to
reach
the
destination
network.
In
other
words,
it
is
the
interface
to
which
the
destination
IP
range
is
connected,
either
directly
or
through
a
router.
The
interface
can
be
any
logical
interface.
This
includes
Ethernet
interfaces
as
well
as
VPN
tunnels.
•
Network
This
is
the
destination
network
IP
address
range
that
is
reached
via
the
specified
interface.
The
route
chosen
from
a
routing
table
is
the
one
that
has
a
destination
IP
range
that
includes
the
IP
address
being
sought.
If
there
is
more
than
one
such
matching
route,
the
route
chosen
is
the
one
that
has
the
smallest
IP
address
range
and
lowest
metric.
The
destination
network
all
‐
nets
‐
ip4
is
usually
always
used
in
the
route
for
public
Internet
access
via
an
ISP.
As
its
name
suggests,
all
‐
nets
‐
ip4
corresponds
to
all
IP4
Internet
addresses,
and
the
route
for
this
address
is
sometimes
referred
to
as
the
default
route
since
it
is
chosen
when
no
other
match
can
be
found.
•
Gateway
This
is
the
IP
address
of
the
gateway
that
is
the
next
router
in
the
path
to
the
destination
network.
This
is
optional.
If
the
destination
network
is
connected
directly
to
the
interface,
this
is
not
needed.
When
a
router
lies
between
the
SEG
and
the
destination
network,
a
gateway
IP
must
be
specified.
For
example,
if
the
route
is
for
public
Internet
access
via
an
ISP,
the
public
IP
address
of
the
ISP’s
gateway
router
would
be
specified.
•
Local
IP
address
This
property
usually
does
not
need
to
be
specified.
If
it
is,
the
SEG
responds
to
ARP
queries
sent
to
this
address.
The
Local
IP
Address
property
on
page
89
section
explains
this
property
in
more
depth.
•
Metric
This
is
a
metric
value
assigned
to
the
route
and
used
as
a
weight
when
performing
comparisons
between
alternate
routes.
If
two
routes
are
equivalent
but
have
different
metric
values
then
the
route
with
the
lowest
metric
value
is
taken.