© Copyright Lenovo 2018
277
Chapter 17. DHCP Snooping
DHCP
snooping
provides
security
by
filtering
untrusted
DHCP
packets
and
by
building
and
maintaining
a
DHCP
snooping
binding
table.
This
feature
is
applicable
only
to
IPv4
and
only
works
in
non
‐
stacking
mode.
An
untrusted
interface
is
a
port
that
is
configured
to
receive
packets
from
outside
the
network
or
firewall.
A
trusted
interface
receives
packets
only
from
within
the
network.
By
default,
all
DHCP
ports
are
untrusted.
The
DHCP
snooping
binding
table
contains
the
MAC
address,
IP
address,
lease
time,
binding
type,
VLAN
number,
and
port
number
that
correspond
to
the
local
untrusted
interface
on
the
switch;
it
does
not
contain
information
regarding
hosts
interconnected
with
a
trusted
interface.
By
default,
DHCP
snooping
is
disabled
on
all
VLANs.
You
can
enable
DHCP
snooping
on
one
or
more
VLANs.
You
must
enable
DHCP
snooping
globally.
To
enable
this
feature,
enter
the
following
commands:
Note:
When
you
make
a
DHCP
release
from
a
client,
the
switch
does
not
forward
the
Unicast
DHCP
release
packet
to
the
server,
the
entry
is
not
removed
from
the
DHCP
snooping
binding
table,
and
the
counter
for
Received
Request
packets
does
not
increase
even
though
the
release
packet
does
arrive
at
the
switch.
If
you
want
the
DHCP
Renew/Release
packet
to
be
forwarded
to
the
server
and
the
corresponding
entry
removed
from
the
DHCP
snooping
binding
table,
configure
an
interface
IP
address
with
the
same
subnet
in
the
same
VLAN.
NE2552E(config)#
ip dhcp snooping vlan
<vlan
number(s)>
NE2552E(config)#
ip dhcp snooping
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