20110607

DHCP Server Interview Questions and Answers - Part III


16. Is a DHCP server "supposed to" be able to support a BOOTP client?
The RFC on such interoperability (1534) is clear: "In summary, a DHCP server:
... MAY support BOOTP clients," (section 2). The word "MAY" indicates such
support, however useful, is left as an option.
A source of confusion on this point is the following statement in section 1.5 of
RFC 1541: "DHCP must provide service to existing BOOTP clients." However, this
statement is one in a list of "general design goals for DHCP", i.e. what the
designers of the DHCP protocol set as their own goals. It is not in a list of
requirements for DHCP servers.

17. Is a DHCP client "supposed to" be able to use a BOOTP server?
The RFC on such interoperability (1534) is clear: "A DHCP client MAY use a reply
from a BOOTP server if the configuration returned from the BOOTP server is
acceptable to the DHCP client." (section 3). The word "MAY" indicates such
support, however useful, is left as an option.

18. Can a DHCP client or server make a DNS server update the client's DNS entry to match the client's dynamically assigned address?
RFCs 2136 and 2137 indicate a way in which DNS entries can be updated
dynamically. Using this requires a DNS server that supports this feature and a
DHCP server that makes use of it. The RFCs are very recent (as of 5/97) and
implementations are few. In the mean time, there are DNS and DHCP servers
that accomplish this through proprietary means.

19. 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.

20. When will the server to server protocol be defined?
The DHC WG of the IETF is actively investigating the issues in inter-server
communication. The protocol should be defined "soon".

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