Configuring Dhcp Snooping - SMC Networks SMCGS10C-SMART Management Manual

C DHCP
ONFIGURING
S
NOOPING
Use the DHCP Snooping Configuration page to filter IP traffic on insecure
ports for which the source address cannot be identified via DHCP snooping.
The addresses assigned to DHCP clients on insecure ports can be carefully
controlled using the dynamic bindings registered with DHCP Snooping (or
using the static bindings configured with IP Source Guard). DHCP snooping
allows a switch to protect a network from rogue DHCP servers or other
devices which send port-related information to a DHCP server. This
information can be useful in tracking an IP address back to a physical port.
P
ATH
Configuration, Security, Network, DHCP, Snooping
C U
OMMAND SAGE
DHCP Snooping Process
Network traffic may be disrupted when malicious DHCP messages are
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received from an outside source. DHCP snooping is used to filter DHCP
messages received on a non-secure interface from outside the network
or fire wall. When DHCP snooping is enabled globally and enabled on a
VLAN interface, DHCP messages received on an untrusted interface
from a device not listed in the DHCP snooping table will be dropped.
Table entries are only learned for trusted interfaces. An entry is added
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or removed dynamically to the DHCP snooping table when a client
receives or releases an IP address from a DHCP server. Each entry
includes a MAC address, IP address, lease time, VLAN identifier, and
port identifier.
When DHCP snooping is enabled, DHCP messages entering an
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untrusted interface are filtered based upon dynamic entries learned via
DHCP snooping.
Filtering rules are implemented as follows:
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If the global DHCP snooping is disabled, all DHCP packets are
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forwarded.
If DHCP snooping is enabled globally, all DHCP packets are
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forwarded for a trusted port. If the received packet is a DHCP ACK
message, a dynamic DHCP snooping entry is also added to the
binding table.
If DHCP snooping is enabled globally, but the port is not trusted, it
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is processed as follows:
If the DHCP packet is a reply packet from a DHCP server
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(including OFFER, ACK or NAK messages), the packet is
dropped.
If a DHCP DECLINE or RELEASE message is received from a
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client, the switch forwards the packet only if the corresponding
entry is found in the binding table.
If a DHCP DISCOVER, REQUEST or INFORM message is received
■
from a client, the packet is forwarded.
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C 4
HAPTER
Configuring Security