3
Addressing
60
After
the
ARP
entry
expiration
time,
the
SEG
will
learn
the
new
MAC
address
of
the
host
but
sometimes
it
may
be
necessary
to
manually
force
the
update.
The
easiest
way
to
achieve
this
is
by
flushing
the
ARP
cache.
This
deletes
all
dynamic
ARP
entries
from
the
cache
and
forces
the
SEG
to
issue
new
ARP
queries
to
discover
the
MAC/IP
address
mappings
for
connected
hosts.
Flushing
can
be
done
with
the
CLI
command
arp
‐
flush
.
Example: Flushing the ARP cache
This
example
shows
how
to
flush
the
ARP
cache
from
within
the
CLI.
Device:/>
arp
‐
flush
ARP
cache
of
all
interfaces
flushed.
Changing the ARP cache size
By
default,
the
ARP
cache
is
able
to
hold
4096
ARP
entries
at
one
time.
This
is
adequate
for
most
situations.
On
rare
occasions,
such
as
when
there
are
several
very
large
LANs
directly
connected
to
the
security
gateway,
it
may
be
necessary
to
increase
this
value.
This
can
be
done
by
modifying
the
setting
ARPCacheSize
property
in
the
ARPTableSettings
object.
Example 1: Changing the ARP cache size
This
example
shows
how
to
change
the
size
of
the
SEG
ARP
cache
to
hold
8192
entries.
Device:/>
set
Settings
ARPTableSettings
ARPCacheSize=8192
Modified
ARPTableSettings.
Hash
tables
are
used
to
rapidly
look
up
entries
in
the
ARP
cache.
For
maximum
efficiency,
a
hash
table
should
be
twice
as
large
as
the
entries
it
is
indexing,
so
if
the
largest
directly
connected
network
contains
500
IP
addresses,
the
size
of
the
ARP
entry
hash
table
should
be
at
least
1000.
You
can
modify
the
setting
ARPHashSize
to
reflect
specific
network
requirements.
The
default
value
of
this
setting
is
512
.
Example 2: Changing the ARP hash size
This
example
shows
how
to
change
the
SEG
ARP
hash
size.
Device:/>
set
Settings
ARPTableSettings
ARPHashSize=1024
Modified
ARPTableSettings.
