CCNA 1 v7 Modules 16 – 17: Building and Securing a Small Network – Test Online

Hint

Worms are able to self-replicate and exploit vulnerabilities on computer networks without user participation.

Hint

Threat actors frequently attempt to access devices over the internet through communication protocols. Some of the most popular remote exploits are as follows:

• Man-In-the-middle attack (MITM) – The threat actor gets between devices in the system and intercepts all of the data being transmitted. This information could simply be collected or modified for a specific purpose and delivered to its original destination.
• Eavesdropping attack – When devices are being installed, the threat actor can intercept data such as security keys that are used by constrained devices to establish communications once they are up and running.
• SQL injection (SQLi) – Threat actors uses a flaw in the Structured Query Language (SQL) application that allows them to have access to modify the data or gain administrative privileges.
• Routing attack – A threat actor could either place a rogue routing device on the network or modify routing packets to manipulate routers to send all packets to the chosen destination of the threat actor. The threat actor could then drop specific packets, known as selective forwarding, or drop all packets, known as a sinkhole attack.

Hint

Authentication, authorization, and accounting are network services collectively known as AAA. Authentication requires users to prove who they are. Authorization determines which resources the user can access. Accounting keeps track of the actions of the user.

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The login block-for command sets a limit on the maximum number of failed login attempts allowed within a defined period of time. If this limit is exceeded, no further logins are allowed for the specified period of time. This helps to mitigate brute-force password cracking since it will significantly increase the amount of time required to crack a password. The exec-timeout command specifies how long the session can be idle before the user is disconnected. The service password-encryption command encrypts the passwords in the running configuration. The banner motd command displays a message to users who are logging in to the device.

Hint

The login and password cisco commands are used with Telnet switch configuration, not SSH configuration.

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Secure Shell (SSH) is a protocol that provides a secure management connection to a remote device. SSH provides security by providing encryption for both authentication (username and password) and the transmitted data. Telnet is a protocol that uses unsecure plaintext transmission. SSH is assigned to TCP port 22 by default. Although this port can be changed in the SSH server configuration, the port is not dynamically changed. SSH does not use IPsec.

Hint

SSH provides a secure method for remote access to hosts by encrypting network traffic between the SSH client and remote hosts. Although both Telnet and SSH request authentication before a connection is established, Telnet does not support encryption of login credentials.

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An intrusion prevention system (IPS) provides real-time detection and blocking of attacks.

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Using different defenses at various points of the network creates a layered approach.

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Redundancy attempts to remove any single point of failure in a network by using multiple physically cabled paths between switches in the network.

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An important prerequisite for considering network growth is to understand the type and amount of traffic that is crossing the network as well as the current traffic flow. By using a protocol analyzer in each network segment, the network administrator can document and analyze the network traffic pattern for each segment, which becomes the base in determining the needs and means of the network growth.

Hint

In the output of the ping command, an exclamation mark (!) indicates a response was successfully received, a period (.) indicates that the connection timed out while waiting for a reply, and the letter “U” indicates that a router along the path did not have a route to the destination and sent an ICMP destination unreachable message back to the source.

Hint

By issuing the ping command without a destination IP address in privileged EXEC mode, the Cisco IOS enters extended ping mode. This allows the user to implement extended commands which include source IP address.​

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While analyzing historical reports an administrator can compare host-to-host timers from the ping command and depict possible latency issues.​

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The most common indicators of a ping issued from the Cisco IOS are “!”, “.”, and “U”. The “!” indicates that the ping completed successfully, verifying connectivity at Layer 3. The “.” may indicate that a connectivity problem, routing problem, or device security issue exists along the path and that an ICMP destination unreachable message was not provided. The “U” indicates that a router along the path may not have had a route to the destination address, and that it responded with an ICMP unreachable message.

Hint

In networks today, a failed ping could mean that the other devices on the network are blocking pings. Further investigation such as checking network connectivity from other devices on the same network is warranted.

Hint

The tracert utility is used to identify the path a packet takes from source to destination. Tracert is commonly used when packets are dropped or not reaching a specific destination.

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The show cdp neighbors command can be used to prove that Layer 1 and Layer 2 connectivity exists between two Cisco devices. For example, if two devices have duplicate IP addresses, a ping between the devices will fail, but the output of show cdp neighbors will be successful. The show cdp neighbors detail could be used to verify the IP address of the directly connected device in case the same IP address is assigned to the two routers.

Hint

The show cdp neighbors detail command reveals much information about neighboring Cisco devices, including the IP address, the capabilities, host name, and IOS version. The show interfaces and show version commands display information about the local device.

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The value of the configuration register can be verified with the show version command.

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Debug messages, like other IOS log messages, are sent to the console line by default. Sending these messages to the terminal lines requires the terminal monitor command.

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A structured network troubleshooting approach should include these steps in sequence:

1. Identify the problem.
2. Establish a theory of probable causes.
3. Test the theory to determine cause.
4. Establish a plan of action to resolve the issue.
5. Verify full system functionality and implement preventive measures.
6. Document findings, actions, and outcomes.

Hint

The nslookup command can be used to look up information about a particular DNS name in the DNS server. The information includes the IP address of the DNS server being used as well as the IP address associated with the specified DNS name. This command can help verify the DNS that is used and if the domain name to IP address resolution works.

Hint

Dynamic Host Configuration Protocol (DHCP) can be used to allow end devices to automatically configure IP information, such as their IP address, subnet mask, DNS server, and default gateway. The DNS service is used to provide domain name resolution, mapping hostnames to IP addresses. Telnet is a method for remotely accessing a CLI session of a switch or router. Traceroute is a command used to determine the path a packet takes as it traverses the network.

Hint

The show ip route command is used to display the IP routing table of the router. The IP routing table will show a list of known local and remote networks and the interfaces that the router will use to reach those networks.

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Executive timeouts allow the Cisco device to automatically disconnect users after they have been idle for the specified time. Console, vty, and aux ports can be configured with executive timeouts.

Hint

SSH is automatically enabled after the RSA keys are generated. Setting user privilege levels and configuring role-based CLI access are good security practices but are not a requirement of implementing SSH.

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Because worms take advantage of vulnerabilities in the system itself, the most effective way to mitigate worm attacks is to download security updates from the operating system vendor and patch all vulnerable systems.

Hint

The ping utility tests end-to-end connectivity between the two hosts. However, if the message does not reach the destination, there is no way to determine where the problem is located. On the other hand, the traceroute utility (tracert in Windows) traces the route a message takes from its source to the destination. Traceroute displays each hop along the way and the time it takes for the message to get to that network and back.

Hint

Telnet sends passwords and other information in clear text, while SSH encrypts its data. FTP and HTTP do not provide remote device access for configuration purposes.

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The missing command to complete the SSH configuration is transport input ssh in line vty 0 4 mode.The commands service password-encryption and enable secret class do configure secure features on the router, but are not required to configure SSH. The command ip domain-name cisco.com is not required because the command ip domain-name span.com has been used.

Hint

Rules for strong passwords: * minimum of 8 characters, preferably 10. * use complex combinations of numbers, special characters, and upper and lower case letters. * avoid repetition, common dictionary words, letter or number sequences. * avoid names of children, relatives, pets, birthdays, or any easily identifiable personal information. * can be created by misspelling words or replacing vowels with numbers or special characters.