Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

DHCP related query and answers

DHCP- Dynamic Host configuration protocol

DHCP is also known as BOOTP

DHCP uses DORA process


D- DHCP Discover Packet to the DHCP Server

O- DHCP Offer packet to the DHCP Client

R- DHCP Request to the DHCP Server

A- DHCP Ack to to the DHCP Clent

----------------------------------------------Some IMP Questions and answers--------------------------

Q. IF DHCP server is on another network then how IP phone get IP address?

When IP Phone reboot or Connected to Switch IP Phone send DHCP request to DHCP server, If

DHCP server is not available and Router connected to IP Phone configured as IP Helper then

Router take request from IP Phone and send request to DHCP server connected to other network.

To allocate IP address with correct IP pool router send IP address of interface, on which interface

request is received. 


DHCP is also configure for device with more information called option.

IP Address               From Scope

Subnet MASK          Option 1

Default Gateway       Option 3

DNS Server              Option 6

SIP Server               Option 120       192.168.87

TFTP Server             Option 150

VLAN ID(802.1Q)     Option 132        2

L2 802.1p Priority    Option 133        6

L3 Priority              Option 134        46


Q. Initial IP Discovery process start with Brodcast or Not ?

--> Yes

Q. How you can check IP config on Windwos? IT help to understand DHCP flow use Wireshark and interface with your LAN card.

--> Goto START/RUN CMD(Command line) > ipconfig /all >> gives current IP address,Subnet mask,default gateway, MAC address

          ipconfig /Release >> Release IP Address  After this command get IP address

          ipconfig /Renew >> Get New IP Address    After this command get new IP Address

Q. IF you have multiple subnet and single DHCP server then what needed on Network router to assist to give IP address.

--> IP Helper command must be configured on router, so router send reuest to DHCP server on another network.

Q. Group of IP address configured on DHCP server is called as ?


Cisco Employee

DHCP related query and answers

Hello Sandeep, in this case the ip request would be recieved from the same voice interface on which the ip helper-address was assigned.

By using the ip helper-address command, a router can be configured to accept a broadcast request for a UDP service and then forward it as a unicast to a specific IP address


Nitin Kharbanda

Community Member

DHCP related query and answers

Thanks for additional information

CreatePlease to create content