Rachel is managing a network that has two groups of client machines separated by a router. The
machines on the same segment as the DHCP server are correctly configured, whereas the
machines on the other sides of the router are not. Rachel also has a domain name server on the
network. What should Rachel do to her network to ensure that all client machines are correctly
configured?
A.
Add a DNS server to the same segment that has the DHCP server.
B.
Add a DNS server to the segment that does not have the DHCP server.
C.
Add a DHCP relay agent to the same segment that has the DHCP server.
D.
Add a DHCP relay agent to the segment that does not have the DHCP server.
Explanation:
DHCP uses broadcasts for all four phases (DORA) of its process. This requires broadcasts to get
from the client to the DHCP server, and from the DHCP server to the client. The problem is that
between these two subnets is a router that does not pass broadcasts. Now there is an exception,
and that is when the router is equipped with the BOOTP RFC, which allows the packets to pass.
(DHCP is based on BOOTP). However, not all routers have this modification, or have this
modification turned on. Unless specified in the question, the RFC is assumed not present or
enabled. That leaves the use of a relay agent. The DHCP relay agent intercepts the broadcasts,
and then communicates directly with the DHCP server to pass the requests back and forth. In
order for the relay agent to hear the broadcasts, it must be on the orphaned segment, the segment
that does not have a DHCP server. If the relay agent is placed on the segment with the DHCP
relay server, then it will not hear the broadcasts from the other segment, because if it did, then we
never needed the relay agent in the first place.
Incorrect Answers:
A: DNS services are not used by DHCP. DHCP does all its work via broadcasts, and does not use
or refer to DNS or WINS.
B: DNS services are not used by DHCP. DHCP does all its work via broadcasts, and does not use
or refer to DNS or WINS.
C: The problem is that the machines that are separated by the router are not receiving a
configuration. Since the client is broadcasting the discovery packet, and the router is not passing
broadcasts, the relay agent on the other side of the router will not get the discovery packet. The
agent is in fact on the wrong side of the router.