Important Question and Answer -DHCP
Today we are discuss some important question and answer dynamic host configuration protocol purpose third part.
Q:-01:- Should I deny unknown clients
Yeah we can,
Once all client are put on fixed IP using DHCP, we deny dynamic allocation to unknown clients via the option ‘deny unknown- clients’. Clients whose MAC addresses are not explicitly listed in the ‘host’ declaration will not receive an IP address. Not serving unknown clients is very important from very security point of view. This option has to be put right on top of dhcpd.conf before any subnet declaration.
Q:-02:-What is a DHCP lease?
A DHCP lease is the amount of time that the DHCP server grants to the DHCPclient permission to use a particular IP address. A server allows its administrator to set the lease time.
Q:-03:-How does DHCP and BOOTP handle multiple subnets?
For the situations where there is more than one LAN, each with its own subnet number, there are two ways. First of all, you can set up a separate server on each subnet.Secondly,a feature of some routers known as “BOOTP forwarding “to forward DHCP or BOOTP requests to a server on another subnet and to forward the replies back to the client. The part of such a router (or server acting as a router) that does this is called a “BOOTP forwarding agent”. Typically you have to enable it on the interface to the subnet to be served and have to configure it with the IP address of the DHCP or BOOTP server. On a Cisco router, the address is known as the “UDP Helper Address”.
Q:- 04:- Can a DHCP server back up another DHCP server?
You can have two or more servers handing out leases for different addresses. If each has a dynamic pool accessible to the same clients, then even if one server is down, one of those clients can lease an address from the other server.
However, without communication between the two servers to share their information on current leases, when one server is down, any client with a lease from it will not be able to renew their lease with the other server. Such communication is the purpose of the “server to server protocol” (see next question).It is possible that some server vendors have addressed this issue with their own proprietary server-to –server communication.
Q:-05:-In a sub netted environment, how does the DHCP server discover what subnet a request has come from?
DHCP client messages are sent to off-net servers by DHCP relay agents, which are often a part of an IP router. The HCP relay agent records the subnet from which the message was received in the DHCP message header for use by the DHCP server.
Note: a DHCP relay agent is the same thing as a BOOTP relay agent, and technically speaking, the latter phrase is correct.