3com 5500-SI Manual Do Utilizador

C

HAPTER

 10: DHCP S

ERVER

 C

ONFIGURATION

receives a response or the number of the sent ICMP packets reaches the specified 
maximum number. The DHCP server assigns the IP address to the DHCP client only 
when no response is received during the whole course. Such a mechanism ensures an 
IP address is assigned to one DHCP client exclusively.

A DHCP server performs ping tests to detect potential IP address conflicts, while a 
DHCP client uses ARP packets to detect IP address conflicts

.

Option 184 is an RFC reserved option, and the information it carries can be 
customized. 3Com defines four proprietary sub-options for this option, enabling the 
DHCP server to put the information required by a DHCP client in the response packet 
to the client. The four sub-options of option 184 mainly carry information about 
voice. The following lists the sub-options and the carried information:

■

Sub-option 1: IP address of the network call processor (NCP-IP).

■

Sub-option 2: IP address of the alternate server (AS-IP).

■

Sub-option 3: Voice VLAN configuration.

■

Sub-option 4: Fail-over call routing.

■

NCP-IP

The NCP-IP sub-option carries the IP address of the network call processor (NCP). 
When used in option 184, this sub-option must be the first sub-option, that is, 
sub-option 1.

The IP address of the NCP server carried by sub-option 1 of option 184 is intended 
for identifying the server acting as the network call controller and the server used 
for application downloading.

■

AS-IP

The AS-IP sub-option carries the IP address of the alternate server (AS), and is the 
second sub-option of option 184, that is, sub-option 2. The AS-IP sub-option takes 
effect only when sub-option 1 (that is, the NCP-IP sub-option) is defined.

The alternate NCP server identified by sub-option 2 of option 184 acts as the 
backup of the NCP server and is used only when the IP address carried by the 
NCP-IP sub-option is unreachable or invalid.

■

Voice VLAN Configuration

The voice VLAN configuration sub-option carries the ID of the voice VLAN and the 
flag indicating whether the voice VLAN identification function is enabled. This 
sub-option is the third sub-option of option 184, that is, sub-option 3.

Table 128   Configure IP address detecting

Enter system view

-

Set the maximum 
number of ICMP 
packets a DHCP server 
sends in a ping test 

dhcp server ping packets 
number

Optional
By default, a DHCP server performs the 
ping operation twice to test an IP 
address.

Set the response 
timeout time of each 
ICMP packet

dhcp server ping timeout 
milliseconds

Optional
The default timeout time is 500 
milliseconds.