3
Addressing
59
Example: Displaying the ARP cache
The
contents
of
the
ARP
cache
can
be
displayed
from
within
the
CLI.
This
example
displays
the
entries
of
the
sfp1
interface.
Device:/>
arp
‐
show
ARP
cache
of
iface
sfp1:
Dynamic
10.4.0.1
=
1000:0000:4009
Expire=196
Dynamic
10.4.0.165
=
0002:a529:1f65
Expire=506
Expires value
The
third
column
in
the
sample
table
and
CLI
output,
Expires
,
is
used
to
indicate
for
how
much
longer,
in
seconds,
the
ARP
entry
will
be
valid.
For
example,
the
first
entry
in
the
above
CLI
output
has
an
expiration
value
of
196,
which
means
that
this
entry
will
be
rendered
invalid
and
removed
from
the
ARP
cache
in
196
seconds.
If
traffic
is
going
to
be
sent
to
the
10.4.0.1
IPv4
address
after
the
expiration,
the
SEG
will
issue
a
new
ARP
request.
The
default
expiration
time
for
dynamic
ARP
entries
is
900
seconds
(15
minutes).
This
can
be
changed
by
modifying
the
advanced
setting
ARPExpire
.
Example 1: Changing the ARPExpire setting
This
example
shows
how
to
change
the
number
of
seconds
for
the
ARPExpire
setting.
Device:/>
set
Settings
ARPTableSettings
ARPExpire=1800
Modified
ARPTableSettings.
The
advanced
setting
ARPExpireUnknown
specifies
how
long
the
SEG
will
remember
addresses
that
cannot
be
reached.
This
limit
is
needed
to
ensure
that
the
SEG
does
not
continuously
request
such
addresses.
The
default
value
for
this
setting
is
3
seconds.
Example 2: Changing the ARPExpireUnknown setting
This
example
shows
how
to
change
the
number
of
seconds
for
the
ARPExpireUnknown
setting.
Device:/>
set
Settings
ARPTableSettings
ARPExpireUnknown=6
Modified
ARPTableSettings.
Flushing the ARP cache
If
a
host
in
a
network
is
replaced
with
new
hardware
and
retains
the
same
IP
address,
it
will
probably
have
a
new
MAC
address.
If
the
SEG
has
an
old
ARP
entry
for
the
host
in
its
ARP
cache,
that
entry
will
become
invalid
because
of
the
changed
MAC
address.
This
will
cause
data
to
be
sent
to
the
host
over
Ethernet
that
will
never
reach
its
destination.
