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Juniper Exam JN0-351 Topic 5 Question 15 Discussion

Actual exam question for Juniper's JN0-351 exam
Question #: 15
Topic #: 5
[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.


Contribute your Thoughts:

Shelton
5 months ago
I wonder if disabling those features would solve the problem.
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Gerri
5 months ago
That makes sense, Victor. Both static IP address and MAC limiting can prevent entries in the snooping database.
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Victor
5 months ago
I believe another reason could be that MAC limiting is enabled on the interface.
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Shelton
5 months ago
I agree with Gerri. That could be one of the reasons for the issue.
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Gerri
5 months ago
I think the reason could be that the device connected has a static IP address.
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Flo
6 months ago
That makes sense. So maybe it's a combination of both static IP and MAC limiting.
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Shannon
6 months ago
I think another reason could be that MAC limiting is enabled on the interface.
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Pearly
6 months ago
I agree with That could definitely be one reason.
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Flo
6 months ago
I think the reason could be that the device connected has a static IP address.
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Quentin
7 months ago
You know, I'm just happy they're not asking us about the inner workings of a quantum computer. That would really throw me for a loop!
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Josephine
7 months ago
Hmm, MAC limiting and dynamic ARP inspection both seem like they could potentially impact DHCP snooping. But a static IP address? That's an interesting one.
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Vashti
6 months ago
Option C may also be a reason, a static IP address could bypass DHCP snooping.
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Mireya
6 months ago
I agree, MAC limiting could prevent entries in the snooping database.
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Caitlin
6 months ago
I think option B could be one reason.
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Linette
7 months ago
Okay, let's start by looking at the options. A DHCPRELEASE sounds like it could be a valid reason, but what about the other choices?
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Vincenza
7 months ago
Ah, I see. This is testing our knowledge of DHCP and how it interacts with the switch configuration. Let's see what we can come up with here.
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Elliott
7 months ago
Ooh, this is a good one! I have some experience with DHCP snooping, so let me share my thoughts.
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Chandra
7 months ago
Hmm, this question seems a bit tricky. I'm not too familiar with DHCP snooping, so I'll have to think about this one carefully.
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