IP Configuration
IPv4 Management and Interfaces
298 Cisco 350, 350X and 550X Series Managed Switches, Firmware Release 2.4, ver 0.4
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How the DHCP Snooping Binding Database is Built
The following describes how the device handles DHCP packets when both the DHCP client
and DHCP server are trusted. The DHCP Snooping Binding database is built in this process.
DHCP Trusted Packet Handling
The actions are:
STEP 1 Device sends DHCPDISCOVER to request an IP address or DHCPREQUEST to accept an IP
address and lease.
STEP 2 Device snoops packet and adds the IP-MAC information to the DHCP Snooping Binding
database.
STEP 3 Device forwards DHCPDISCOVER or DHCPREQUEST packets.
STEP 4 DHCP server sends DHCPOFFER packet to offer an IP address, DHCPACK to assign one, or
DHCPNAK to deny the address request.
STEP 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.
STEP 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 Arriving from Untrusted
Ingress Interface
Arriving from Trusted Ingress
Interface
DHCPDISCOVER Forward to trusted
interfaces only.
Forwarded to trusted interfaces only.
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