This article will cover the Infrastructure Services section of the CCNA Routing and Switching exam.

What Percent of the Exam Covers Infrastructure Services?

The exam consists of 60-70 questions. Since the Infrastructure Services section represents 10% of the entire curriculum, you can expect six or seven questions on the topics covered in this section.

What Topics are Covered in This Exam?

The section contains five major topics: Domain Name Server (DNS), Dynamic Host Control Protocol (DHCP), Hot Standby Router Protocol (HSRP), Network Address Translation (NAT) and Network Time Protocol (NTP).

Let’s go through these topics and see what you need to know so you can be prepared to get the best score.

DNS Operation

You should have a clear understanding of what DNS is and how DNS is used to resolve names. It wouldn’t hurt to know the TCP and UDP ports that this service is using, either. You should know how to build a host table and how to configure the devices to use a DNS server. Going further, you should know how to improve the name resolution performance by using a cache, how to start the DNS server on the device, and how to provide a sequence of domain names. You should be familiar with how to specify a default domain for the hostnames and how to enable DNS lookup on specific interfaces.

You should also be familiar with troubleshooting techniques for DNS client issues. For instance, you need to determine if the problem is with the client or if there is a problem with the DNS server (not reachable, not configured). The section covering DNS is not complicated and, by going through the documentation once and testing a few commands in the lab, you should become knowledgeable enough to get most of the points during the exam.

Configuration, Verification and Troubleshooting DHCP

The DHCP curriculum is more advanced and requires you to spend more time studying. This is not only because the documentation is extensive, but because there are some interesting details in the technology and configuration steps.

It is imperative to know the difference between a DHCP client and a DHCP server in terms of functionalities. Again, it would not hurt to know the protocol and ports used by each of these.

You will need to be familiar with how a DHCP server dynamically assigns IP addresses to hosts (the messages that are exchanged between the server and the client for the client to receive an IP address through DHCP), how to check which IP addresses were assigned using DHCP, what happens with an IP address when there is a conflict for that IP address, and how to check the duplicates for that IP addresses.

As for configuration and operation, you should know what the minimum is to configure a router as a DHCP server and what your options are to achieve different things, such as reachability outside the local subnet. Also, you should be aware that DHCP uses default values for some mandatory parameters if they are not specifically configured, and know those default values.

It is important to remember that not only hosts that can be DHCP clients; routers and switches can also take on that role. Therefore, you should know how to configure a network device to be a DHCP client.

Because a device can be something other than a DHCP server or DHCP client (namely, a DHCP relay), you will need to know how and where the configuration pertaining to DHCP relay has to be applied, based on the client’s location in the network.

With regard to troubleshooting DHCP-related issues, you should be aware of how to check address assignment failures, as well as how to check the IP addresses for which there is a conflict.

As stated, this is an important section and you should focus your time trying to understand the operation of DHCP and how to configure a device to act as a DHCP server. Extensive lab time is recommended when studying the DHCP feature.

Configuration, Verification and Troubleshooting HSRP

The next section covers one of the first hop redundancy protocols, HSRP. Since it was the first protocol of its kind, it is well-documented, and the Cisco official documentation covers multiple scenarios for how the protocol can be deployed. Although there are multiple FHRPs, some proprietary and some standard-based, only HSRP is covered in the CCNA exam.

To start with, you will need to know how the protocol works and how it ensures high availability. It’s also important to know the format of the HSRP virtual MAC address.

You should be familiar with the protocol states, the minimum configuration required to configure HSRP, how the active router is chosen, and what happens when the default HSRP configuration is applied. For this last topic, you will also need to know what the default values for specific parameters are. Since the purpose of the protocol is to provide redundancy, you will need to know how the device operates when there is a failure of the active router and how the device might operate after a recovery, based on preemption in the configuration.

Since the protocol’s inception, a new version has been released, so you will need to know the key difference between original HSRP and HSRPv2.

Continuing from the format of the virtual MAC address, you should understand how load balancing can be achieved using HSRP.

For verification, you should be able to correctly identify from HSRP outputs which device is the active one, what the priority is, and the timer values. For troubleshooting, you need to take a look at the virtual IP address on both routers to ensure that they are identical, and that the HSRP groups and HSRP versions are identical on the two devices.

As you can see, your study should focus on verification and troubleshooting. The minimal configuration ensures that you can achieve what the protocol intends to do. Starting with this in a lab, you should investigate how the devices keep track of each other and how they communicate, and what happens during a failure.

Configuration, Verification and Troubleshooting NAT

The next topic is NAT, which in my opinion requires more study because you need to understand various types of NAT and NAT names. Therefore, you should have no doubt about what the static NAT, dynamic NAT and overloading can do, and when it is suitable to use any of them. This will help you to choose the right answer when you are asked which NAT flavor suits better in the provided scenario. Beyond that, be certain that inside/outside local/global addresses are clear to you.

In configuring any of these types of NAT there are specific steps that have to be followed, and it is strongly advised that you cover these extensively in the lab because forgetting one of the steps will make the feature unusable. For instance, a simple switch between inside and outside interfaces will cause unnecessary troubleshooting.

As for operation and troubleshooting, there is a pair of commands (show and debug commands) that be used to reveal if NAT works correctly or to provide useful information to fix a potential problem. However, the output of the commands might be irrelevant if you have no solid foundation about how NAT works to determine if what is translated should be translated. This solid foundation is applicable to all concepts but, in the case of NAT, it is even more important compared to the other topics covered by this section of the curriculum.

Configuring and Troubleshooting NTP

The last topic is NTP, which is probably the simplest of those covered in this curriculum section. There are no more than a handful of commands related to NTP that you should be aware of if NTP questions pop up during the exam.

First, it is important to know the two NTP modes that a router can work in and what the requirement is for a router to act as an NTP server if there is no external clock source available. In addition, you might want to understand what the purpose of the authentication is when we talk about NTP, and what the steps are to configure it.

From the commands perspective, you should be aware how to configure the device as an NTP server and as an NTP client, how to check if the device is associated and synchronized with the NTP server, and to determine how far the device is from the NTP source clock.

Where Should I Focus My Study Time?

As stated, this topic does not require extensive study. Configuring the feature in both modes and using the verification commands provided by the supporting documentation will have you ready for the exam. Good luck!

Be Safe

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