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Juniper Exam JN0-351 Topic 4 Question 20 Discussion

Actual exam question for Juniper's JN0-351 exam
Question #: 20
Topic #: 4
[All JN0-351 Questions]

You have DHCP snooping enabled but no entries are automatically created in the snooping database for an interface on your EX Series switch. What are two reasons for the problem? (Choose two.)

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Suggested Answer: B, C

The DHCP snooping feature in Juniper Networks' EX Series switches works by building a binding database that maps the IP address, MAC address, lease time, binding type, VLAN number, and interface information1.This database is used to filter and validate DHCP messages from untrusted sources1.

However, there are certain conditions that could prevent entries from being automatically created in the snooping database for an interface:

MAC limiting: If MAC limiting is enabled on the interface, it could potentially interfere with the operation of DHCP snooping.MAC limiting restricts the number of MAC addresses that can be learned on a physical interface to prevent MAC flooding attacks1. This could inadvertently limit the number of DHCP clients that can be learned on an interface, thus preventing new entries from being added to the DHCP snooping database.

Static IP address: If the device connected to the interface is configured with a static IP address, it will not go through the DHCP process and therefore will not have an entry in the DHCP snooping database1.The DHCP snooping feature relies on monitoring DHCP messages to build its database1, so devices with static IP addresses that do not send DHCP messages will not have their information added.

Therefore, options B and C are correct.Options A and D are not correct because performing a DHCPRELEASE would simply remove an existing entry from the database1, and Dynamic ARP inspection (DAI) uses the information stored in the DHCP snooping binding database but does not prevent entries from being created1.


by Tomas at Jun 01, 2024, 04:08 AM

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Tamekia
1 years ago
This question is as clear as mud. I'll go with B and C, just to be on the safe side. Hey, at least it's not a question about configuring a toaster oven!
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Felix
1 years ago
Hmm, this is a tricky one. I'm guessing B and D are the right answers. MAC limiting and dynamic ARP inspection could both interfere with the DHCP snooping process.
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Shenika
1 years ago
B) MAC limiting is enabled on the interface.
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Sonia
1 years ago
A) The device that is connected to the interface has performed a DHCPRELEASE.
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Dorian
1 years ago
I agree with you, that could be one reason. Another reason might be if MAC limiting is enabled on the interface.
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Yuonne
1 years ago
I think the problem could be because the device has a static IP address.
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Ardella
1 years ago
Definitely B and C. The DHCP snooping database is only populated by DHCP traffic, so if the device has a static IP, there's no DHCP traffic to create the entry.
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Yvette
1 years ago
C) MAC limiting is enabled on the interface.
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Anika
1 years ago
B) The device that is connected to the interface has a static IP address.
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Mica
1 years ago
I think the correct answers are B and C. If MAC limiting is enabled, it won't allow new DHCP entries, and if the device has a static IP, there won't be any DHCP traffic to create the snooping database entry.
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Alyssa
1 years ago
Yes, having a static IP address would also explain why there are no entries in the snooping database.
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Ora
1 years ago
I agree, B and C make sense. MAC limiting would definitely prevent new DHCP entries.
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Kenda
1 years ago
That makes sense. Those are the two reasons that could be causing the issue with DHCP snooping.
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Jutta
1 years ago
I agree, B and C make sense. MAC limiting would definitely prevent new entries, and a static IP means no DHCP traffic.
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Blair
1 years ago
User 2
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Dorothea
1 years ago
User 1
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