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DHCP ACK message, start using the source which server assigned. If received DHCP NAK,
DHCP Client will resend DHCP DISCOVER message.
7.3.2 About DHCP Snooping
The addresses assigned to DHCP clients on insecure ports can be carefully controlled using
the dynamic bindings registered with DHCP Snooping. 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.
Command Usage:
•
Network traffic may be disrupted when malicious DHCP messages are received from
an outside source. DHCP snooping is used to filter DHCP messages received on a
non-secure interface from outside the network or firewall 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 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 untrusted interface
are filtered based upon dynamic entries learned via DHCP snooping.
•
If a DHCP packet from a client passes the filtering criteria, it will only be forwarded
to trusted ports in the same VLAN
•
If a DHCP packet is from server is received on a trusted port, it will be forwarded to
both trusted and untrusted ports in the same VLAN.
•
If DHCP snooping is globally disabled, all dynamic bindings are removed from the
binding table.
Summary of Contents for JTD-2886
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