Using Dhcp - 3Com V7122 User Manual

Using DHCP

When the gateway is configured to use DHCP (DHCPEnable = 1), it attempts to contact the
local DHCP server to obtain the networking parameters (IP address, subnet mask, default
gateway, primary/secondary DNS server and two SIP server addresses). These network
parameters have a 'time limit'. After the time limit expires, the gateway must 'renew' its lease
from the DHCP server.
Note that if the DHCP server denies the use of the gateway's current IP address and
specifies a different IP address (according to RFC 1541), the gateway must change its
networking parameters. If this happens while calls are in progress, they are not automatically
rerouted to the new network address (since this function is beyond the scope of a VoIP
gateway). Therefore, administrators are advised to configure DHCP servers to allow renewal
of IP addresses.
If the gateway's network cable is disconnected and reconnected, a DHCP
renewal is performed (to verify that the gateway is still connected to the same
network).
When DHCP is enabled, the gateway also includes its product name (for example, 'V7122')
in the DHCP 'option 60' Vendor Class Identifier. The DHCP server can use this product
name to assign an IP address accordingly.
After power-up, the gateway performs two distinct DHCP sequences. Only in the
second sequence, DHCP 'option 60' is contained. If the gateway is reset from the
Web/SNMP, only a single DHCP sequence containing 'option 60' is sent.
If DHCP procedure is used, the new gateway IP address, allocated by the DHCP server,
must be detected.
If, during operation, the IP address of the gateway is changed as a result of a
DHCP renewal, the gateway is automatically reset.
To detect the gateway's IP address, follow one of the procedures:
Starting with Boot version 1.92, the gateway can use a host name in the DHCP request.
The host name is set to acl_nnnnn, where nnnnn stands for the gateway's serial number
(the serial number is equal to the last 6 digits of the MAC address converted from Hex to
decimal). If the DHCP server registers this host name to a DNS server, the user can
access the gateway (through a Web browser) using a URL of http://acl_<serial number>
(instead of using the gateway's IP address). For example, if the 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
Contact your System Administrator.
V7122 Gateway User Guide
Figure 123).
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