D-Link DGS-6600-48TS Configuration Guide - Page 486

Volume 9-Network Application / Chapter 49-DHCP Server Configuration • based on client identifier • based on customer vlan tag number • based on service provider vlan tag number • based on IP address of ingress interface • based on IP address of relay agent • based on vendor identifier class • based on user class. Chapter Overview The binding rules (above) are all logical, operational conditions with other rules are set by other "based-on" commands. The ingress DHCPDISCOVER or DHCPREQUEST message must be checked according to the configuration. For example: If user configures an IP address '10.75.60.23' for client if client's MAC address matches 0001.03AA.BC3A, c-tag is 4 and s-tag is 5. Then if the incoming DHCPDISCOVER only matched the MAC address. Server will not assign the specific address '10.75.60.23' to this client. Instead server looks up and assignable address from other matched binding address pool for client. The address pool could also be configured to evaluate client identifier or to accept relay option 82 or not. If this address pool is configured as evaluate client identifier, server evaluates if the client identifier matches the client's hardware type and hardware address if client sends client identifier option. User could configure whether to accept DHCP messages according to if it contains remote ID or circuit ID in option 82 or not by command "accept dhcp relay agent". Please note that the configured IP address may not be within the same subnet as the IP address of the interface which receives the DHCP messages from the MAC/client identifier mapped client. The system administrator must assure the valid route to the assigned IP address in routing table. If unraised, unexpected error result might occurred, e.g. finding if no routes while sending packets out. Also, upon receiving DHCP RELEASE, the device will delete binding information in every address pool if one's IP matched 'ciaddr' in DHCP RELEASE if the 'server identifier' in DHCP RELEASE matched the interface address of the device. Selecting IP address pool When DHCP server received DISCOVER,REQUEST packet, it will first go checking if this incoming packet belongs to which address pool by its MAC address, client-identifier, vlan double tags and other criteria. Then server evaluates client identifier and content in option 82 to decide if to evaluate the content of packet. Note: The DHCP pool name plays an important role. If the DHCP host's request meets the IP address binding rules at more than one DHCP address pools. The pool name in shortest name and lowest alphabet is the only pool allowed to offer the correct IP address to the host. DHCP DISCOVER/REQUEST with 'requested IP address While the device received DHCP message with 'requested IP address' option filled. It will check the validation of this requested IP address according to the following rules. • Check if the requested IP is equal to the address in field 'giaddr' or addressed of local interfaces. • Check if the requested IP is within the range of assignable IP address in address pool chosen by section 40-3-2. DGS-6600 Configuration Guide 486