everypaster.blogg.se

(This is useful if you are applying the same IP addressing policy to DHCP client requests from ports in different VLANs on the same routing switch.) Configuring this option means the management VLAN's IP address appears in the remote ID subfield of all DHCP requests originating with clients connected to the routing switch, regardless of the VLAN on which the requests originate. Use the Management VLAN option if a management VLAN is configured and you want all DHCP clients on the routing switch to use the same IP address. Use the IP address option if the server will apply different IP addressing policies to DHCP client requests from ports in different VLANs on the same routing switch. The relay agent strips off the Option 82 data and forwards the response packet out the port indicated in the response as the Circuit ID (client access port.) Under certain validation conditions described later in this section, a relay agent detecting invalid Option 82 data in a response packet may drop the packet. (Intermediate next-hop routing switches without Option 82 capability can be used to forward-route-client request packets with Option 82 fields.) Response packets from an Option 82 server are routed back to the primary relay agent (routing switch) and include an IP addressing assignment for the requesting client and an exact copy of the Option 82 data the server received with the client request. Other, upstream relay agents used to forward the packet may append their own Option 82 fields, replace the Option 82 fields they find in the packet, forward the packet without adding another field, or drop the packet.

Typically, the first (primary) Option 82 relay agent to receive a client's DHCP request packet appends an Option 82 field to the packet and forwards it toward the DHCP server identified by the IP helper address configured on the VLAN in which the client packet was received. General DHCP-relay operation with Option 82

This operation provides several advantages over DHCP without Option 82: A DHCP server with Option 82 capability can read the appended field and use this data as criteria for selecting the IP addressing it will return to the client through the usual DHCP server response packet. This field includes two suboptions for identifying the routing switch (by MAC address or IP address) and the routing switch port the client is using to access the network. Option 82 enhances this operation by enabling the routing switch to append an Option 82 field to such client requests. Without Option 82, DHCP operation modifies client IP address request packets to the extent needed to forward the packets to a DHCP server. The routing switch can operate as a DHCP relay agent to enable communication between a client and a DHCP server on a different subnet. These include a circuit ID for the incoming circuit and a remote ID that provides a trusted identifier for the remote high-speed modem. The initial suboptions are defined for a relay agent that is co-located in a public circuit access unit.

The relay agent information option is organized as a single DHCP option that contains one or more suboptions that convey information known by the relay agent. The DHCP server echoes the option back verbatim to the relay agent in server-to-client replies, and the relay agent strips the option before forwarding the reply to the client. Servers recognizing the relay agent information option may use the information to implement IP address or other parameter assignment policies. Option 82 is called the relay agent information option and is inserted by the DHCP relay agent when forwarding client-originated DHCP packets to a DHCP server.