Linksys LGS308 User Manual page 138

4. DHCP server sends DHCPOFFER packet to offer an IP address, DHCPACK to assign one,
or DHCPNAK to deny the address request.
5. Device snoops packet. If an entry exists in the DHCP Snooping Binding table that matches
the packet, the device replaces it with IP-MAC binding on receipt of DHCPACK.
6. Device forwards DHCPOFFER, DHCPACK, or DHCPNAK.
The following summarizes how DHCP packets are handled from both trusted and untrusted ports.
The DHCP Snooping Binding database is stored in non- volatile memory.
DHCP Snooping Packet Handling
Packet Type
DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPACK
DHCPNAK
DHCPDECLINE
Packet Type
DHCPRELEASE
DHCPINFORM
DHCPLE AS EQUE RY
Arriving from Untrusted Ingress
Interface
Forward to trusted interfaces
only.
Filter.
Forward to trusted interfaces
only.
Filter.
Filter.
Check if there is information in
the database. If the information
exists and does not match the
interface on which the message
was received, the packet is
filtered. Otherwise, the packet is
forwarded to trusted interfaces
only, and the entry is removed
from database.
Arriving from Untrusted Ingress
Interface
Same as DHCPDECLINE .
Forward to trusted interfaces
only.
Filtered.
Arriving from Trusted Ingress
Forwarded to trusted interfaces
only.
Forward the packet according to
DHCP information. If the
destination address is unknown
the packet is filtered.
Forward to trusted interfaces
only.
Same as DHCPOFFER and an
entry is added to the DHCP
Snooping Binding database.
Same as DHCPOFFER. Remove
entry if exists.
Forward to trusted interfaces
only
Arriving from Trusted Ingress
Interface
Same as DHCPDECLINE .
Forward to trusted interfaces
only.
Forward.
138