subject: CCNA Training - DHCP Bindings [print this page] CCNA Training - DHCP Bindings CCNA Training - DHCP Bindings
DHCP bindings
When you see the term address binding this means that there is a mapping between the IP address of the client and the MAC address. This binding can be configured by you the administrator manually or this can be assigned from a pool of address from the DHCP server.
When you use a Cisco device to assign IP addresses this info in stored in it's NVRAM, or Non-Volatile memory. You may create as many address pools as you wish in a cisco device. When someone mentions the term "manual binding" they are referring to an IP address to MAC address binding carried out by the network administrator whereas an "Automatic binding" is where the IP address of the host has been leased by the DHCP and automatically mapped by the DHCP to the clients MAC address.
DHCP Options and Sub-Options
The DHCP configuration on a Cisco device allows you to specify Options which are viewed as control information for the client and are carried over to the client within the options field of the DHCP offer message. The cisco device will permit you to implement most DHCP options that you may need to customise your network. One of the most commonly use options you will find is option 150. This option is used to notify cisco IP phones what the IP address is of the TFTP server is.
Another common option that is used is option 82 which allows the cisco relay agent to include more detailed information regarding itself when relaying the original discover packet from the client to the DHCP server.
