3Com VCX V7122 SIP VoIP Gateway User Manual 169DHCP SupportWhen the gateway is configured to use DHCP (DHCPEnable = 1), it attempts to contact theenterprise’s DHCP server to obtain the networking parameters (IP address, subnet mask,default gateway, primary/secondary DNS server and SIP server address). These networkparameters have a "time limit". After the time limit expires, the gateway must "renew" itslease from the DHCP server.Note that if the DHCP server denies the use of the gateway's current IP address andspecifies a different IP address (according to RFC 1541), the gateway must change itsnetworking parameters. If this happens while calls are in progress, they are not automaticallyrerouted to the new network address (since this function is beyond the scope of a VoIPgateway). Therefore, administrators are advised to configure DHCP servers to allow renewalof IP addresses.Note: If the gateway's network cable is disconnected and reconnected, a DHCP renewal isperformed (to verify that the gateway is still connected to the same network).When DHCP is enabled, the gateway also includes its product name (e.g., ‘VCX V7122’) inthe DHCP ‘option 60’ Vendor Class Identifier. The DHCP server can use this product nameto assign an IP address accordingly.Note: After power-up, the gateway issues two DHCP requests. Only in the second request,the DHCP ‘option 60’ is contained. If the gateway is reset from the Web/SNMP, only a singleDHCP request containing ‘option 60’ is sent.If DHCP procedure is used, the new gateway IP address, allocated by the DHCP server,must be detected.To detect the gateway’s IP address, follow one of the procedures below: Starting with Bootload software version 1.92, the gateway can use host name in theDHCP request. The host name is set to acl_nnnnn, where nnnnn stands for thegateway’s serial number (the serial number is equal to the last 6 digits of the MACaddress converted from Hex to decimal). If the DHCP Server registers this host name toa DNS server, the user can access the gateway (through a Web browser) using a URL ofhttp://acl_ (instead of using the gateway’s IP address). For example, ifthe gateway’s MAC address is 00908f010280, the DNS name is acl_66176. After physically resetting the gateway its IP address is displayed in the ‘Client Info’column in the BootP/TFTP configuration utility (see Figure 65 on page 195). Contact your System Administrator.BootP SupportUpgrading the VCX V7122When upgrading the VCX V7122 (loading new software onto the gateway) using theBootP/TFTP configuration utility:If, during operation, the IP address of the gateway is changed as a result of aDHCP renewal, the gateway is automatically reset.
