IOS DHCP Server Config

 In 200-301 V2 Ch07: DHCP, CCENT-OLD, Q&A

Today’s sample question gives you a chance to test yourself to find out if you already know a few of the points made in one of the Common Mistake videos in the CCENT Exam Prep LiveLessons video product (video 9.3 in particular). Specifically, this question test you on a couple of details related to the configuration of a DHCP server on a Cisco router.

The Question

Router R1 acts as the DHCP server for the LAN connected to R2. The DHCP server should be ready to assign addresses in the upper half of the range of addresses in subnet The server should also not assign addresses in the lower half of the subnet, particularly addresses already used by router R2 and switch SW2 as shown in the figure. Which answers list a DHCP server configuration setting that would be part of a working configuration that meets these requirements?

A) Use the network /24 command in DHCP pool mode

B) Use the network /25 command in DHCP pool mode

C) The ip dhcp excluded-address command(s) must exclude the address of router R2 (and possibly others)

D) Use the ip dhcp excluded-address command does not have to exclude the address of router R2 (but may list others)


Figure 1: The Network for the DHCP Server Question



Get Deeper Background with CCENT EPL

I chose to write this particular question because of the release of CCENT EPL product. We had selected a few of the videos from that product as samples that anyone can view. One of those Common Mistake videos discusses DHCP server config, specifically those that you need to know to answer this question. So, if you need help with this question, check the CCENT EPL product page, and take about 7 minutes to watch video 9.3, “Configuring an IOS DHCP Server”.


Answer Post in a Few Days!

I’ll post an answer post in a few days. Watch for it! It should be the next post in chronological order as well, so watch for the link at the bottom of this page.

OSPFv2 Enabler #1 - Answers
IOS DHCP Server Config - Answers
Notify of

Newest Most Voted
Inline Feedbacks
View all comments
Thierry Valery

Answer: D

Michael G

Haven’t seen my comments to either this question or the answer page come up yet… ho hum.. I also answered D and am very confused by the answers A and C that Wendell gave. Hoping he can approve the comments and answer my question soon 🙂


Hi Michael,
I have to approve comments until the commenter has made enough to be automatically approved. And I don’t work the blog 7 days a week. I just approved your longer comment from Saturday night.


Hi Wendell,

Nice to see some more updates coming in!

I would say the answer is D.

We can rule out the commands with the network prefix straight away as the DHCP network command requires the full mask and not a prefix.

Answer C is not required as we are handing out DHCP addresses for the /24 network and R1 is in the /24 network.

Supios Guy

I am torn between C or D. I am going with D.


A and C


A and C are the answer


Hi Wendell,

What is the correct answer and why?


disregard…I get it.



I think the correct answers would be A and D.
A is correct because we need to configure the left-most network in a pool to be able to lease adresses to devices in it.
B is incorrect because R2’s LAN IP would not be in a pool entry on R1’s DHCP configuration, so no reply will be sent by R1.
C and D are tricky, because the question specifies that ” The server should also not assign addresses in the lower half of the subnet, particularly addresses already used by router R2″. So if we assume R2 LAN interface never changes its IP, we don’t NEED to exclude its address, because DHCP will test if the IP is already assigned. Assuming we excluded all other lower half IPs, the next address ther DHCP server will try to lease is on the upper half of adresses.


Hi Pedro,
Thanks for the post. I still think answer C is better than D. D leaves the option open to not exclude the .1 address, and rely on the DHCP server to notice that .1 is in use with DHCP conflict resolution. The better answer is to exclude the .1 address, whether it be part of the range from .1 through .127 or not, it’s still excluded with no need to check for a conflict. Just my $.02.


Dear Wendell,
Are B and C the answers?


Hi Nick,
I had a problem with a blog plugin, and it’s fixed now. The link to the answer post should be at the bottom of the page, just above the comments section. But it’s A, C in this case.

Would love your thoughts, please comment.x