© Copyright Lenovo 2017
Chapter 29: Border Gateway Protocol
461
Selecting Route Paths in BGP
BGP
selects
only
one
path
as
the
best
path.
It
does
not
rely
on
metric
attributes
to
determine
the
best
path.
When
the
same
network
is
learned
via
more
than
one
BGP
peer,
BGP
uses
its
policy
for
selecting
the
best
route
to
that
network.
The
BGP
implementation
on
the
CN4093
uses
the
following
criteria
to
select
a
path
when
the
same
route
is
received
from
multiple
peers.
1.
Local
fixed
and
static
routes
are
preferred
over
learned
routes.
2.
With
iBGP
peers,
routes
with
higher
local
preference
values
are
selected.
3.
In
the
case
of
multiple
routes
of
equal
preference,
the
route
with
lower
AS
path
weight
is
selected.
AS
path
weight
=
128
x
AS
path
length
(number
of
autonomous
systems
traversed).
4.
In
the
case
of
equal
weight
and
routes
learned
from
peers
that
reside
in
the
same
AS,
the
lower
metric
is
selected.
Note:
A
route
with
a
metric
is
preferred
over
a
route
without
a
metric.
5.
The
lower
cost
to
the
next
hop
of
routes
is
selected.
6.
In
the
case
of
equal
cost,
the
eBGP
route
is
preferred
over
iBGP.
7.
If
all
routes
have
same
route
type
(eBGP
or
iBGP),
the
route
with
the
lower
router
ID
is
selected.
When
the
path
is
selected,
BGP
puts
the
selected
path
in
its
routing
table
and
propagates
the
path
to
its
neighbors.
Summary of Contents for Flex System Fabric CN4093
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