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Defining VLAN Rules VLAN Rules Overview
OmniSwitch 6600 Family Network Configuration Guide April 2006 page 8-5
DHCP Rules
Dynamic Host Configuration Protocol (DHCP) frames are sent from client workstations to request an IP
address from a DHCP server. The server responds with the same type of frames, which contain an IP
address for the client. If clients are connected to mobile ports, DHCP rules are used to classify this type of
traffic for the purposes of transmitting and receiving DHCP frames to and from the server.
When a mobile port receives a DHCP frame that matches a DHCP rule, the port is temporarily assigned to
the VLAN long enough to forward the DHCP requests within the VLAN broadcast domain. The source
MAC address of the DHCP frame, however, is not learned for that VLAN port association. As a result, the
show mac-address-table command output will not contain an entry for the DHCP source MAC address.
The show vlan port command output, however, will contain an entry for the temporary VLAN port asso-
ciation that occurs during this process.
Once a device connected to a mobile port receives an IP address from the DHCP server, the VLAN port
assignment triggered by the device’s DHCP frames matching a VLAN DHCP rule is dropped unless regu-
lar port traffic matches another rule on that same VLAN. If this match occurs, or the traffic matches a rule
on another VLAN, then the source MAC address of the mobile port’s frames is learned for that VLAN
port association.
DHCP rules are most often used in combination with IP network address rules. A DHCP client has an IP
address of all zeros (0.0.0.0) until it receives an IP address from a DHCP server, so initially it would not
match any IP network address rules.
Binding rules, MAC address rules, and protocol rules also capture DHCP client traffic. The exception to
this is binding rules that specify an IP address as part of the rule, similar to IP network address rule defini-
tions.
The following DHCP rule types are available:
• DHCP MAC Address
• DHCP MAC Range
• DHCP Port
• DHCP Generic