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    Using Option 60 Strings to Forward Client Traffic to Specific DHCP Servers

    The DHCP functionality supports the DHCP vendor class identifier option (option 60). This support allows DHCP relay to compare option 60 strings in received DHCP client packets against strings that you configure on the router. You can use the DHCP relay option 60 feature when providing converged services in your network environment—option 60 support enables DHCP relay to direct client traffic to the specific DHCP server (the vendor-option server) that provides the service that the client requires. Or, as another option, you can configure option 60 strings to direct traffic to the DHCP local server in the current virtual router.

    For example, you might have an environment in which some DHCP clients require only Internet access, while other clients require IPTV service. The clients that need Internet access get their addresses assigned by the DHCP local server on the E Series router (in equal-access mode). Clients requiring IPTV must be relayed to a specific DHCP server that provides the service. To support both types of clients, you configure two option 60 strings on the DHCP relay. Now, when any DHCP client packets are received with option 60 strings configured, the strings are matched against all strings configured on the DHCP relay. If the client string matches the first string you configured, that client is directed to the DHCP local server and gains Internet access. Client traffic with an option 60 string that matches your second string is relayed to the DHCP server that provides the IPTV service. In addition, you can configure a default action, which DHCP relay performs when a client option 60 string does not match any strings you have configured—for example, you might specify that all clients with non-matching strings be dropped.

    Note: You must enter the set dhcp relay command to create and enable DHCP relay before you enter the set dhcp vendor-option command to compare option 60 strings in received DHCP client packets against strings that you configure on the router and forward them to specific DHCP servers. Otherwise, the client traffic that matches the configured option 60 strings are dropped.

    You use the set dhcp vendor-option command to configure vendor-option (option 60) strings to control DHCP client traffic Create DHCP vendor-option servers by configuring DHCP relay to match DHCP option 60 strings and to specify what action to use for the traffic.

    Use the following guidelines when configuring the set dhcp vendor-option command:

    • Use the equals or starts-with keywords to specify a unique string to match, and to configure the action to take for traffic with a matching string:
      • equals—The DHCP client string is an exact match of the specified string
      • starts-with—The DHCP client string is a partial match, from left-to-right, of the specified string. For example, a client string of day matches a starts-with configured string of daytime.
    • Use the following keywords to configure actions for matching strings:
      • local-server—Forward packets to the DHCP local server
      • relay—Forward packets to the DHCP server with the specified IP address
    • Use the default keyword to set the default action to take when the option 60 string does not match a configured vendor-option string. Use the following keywords to configure actions for nonmatching strings:
      • drop—Discard traffic
      • local-server—Forward packets to the DHCP local server
      • proxy-client—Forward traffic to the DHCP proxy client server
      • relay—Forward packets to the DHCP server with the specified IP address
      • relay-server-list—Forward traffic to all non-vendor option DHCP servers. The relay-server-list consists of all non-vendor option servers. Non-vendor option servers are those servers that are configured with the set dhcp relay command but not with the set dhcp vendor-option command.
      • When you configure the first DHCP vendor-option and no default action is specified for a configured DHCP application, the router chooses the default action according to the preference of the DCHP applications. The order of preference from first to last is DHCP local server, DHCP relay, and DHCP proxy client.

    You can map multiple strings to the same DHCP server. However, you cannot map the same vendor option string to multiple servers. An error message is displayed in the CLI interface when you attempt to associate the same option 60 string to more than one server.

    You can configure a maximum of 100 option 60 strings per DHCP relay. Strings can contain a maximum of 254 characters.

    Client packets that have option 60 configured but have no string specified (a string of 0 length) are treated as nonmatching strings and handled accordingly.

     
     

    Published: 2014-08-20