Networking & CCNA

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.

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.

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.

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.

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.

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 terminal monitor command is very important to use when log messages appear. Log messages appear by default when a user is directly consoled into a Cisco device, but require the terminal monitor command to be entered when a user is accessing a network device remotely.

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.

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.

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.

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.

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.

Ping round trip time statistics are shown in milliseconds. The larger the number the more delay. A baseline is critical in times of slow performance. By looking at the documentation for the performance when the network is performing fine and comparing it to information when there is a problem, a network administrator can resolve problems faster.

The -6 option in the command C:\> tracert -6 www.cisco.com is used to force the trace to use IPv6.

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.

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.

A structured network troubleshooting approach should include these steps in sequence:Identify the problem. Establish a theory of probable causes. Test the theory to determine cause. Establish a plan of action to resolve the issue. Verify full system functionality and implement preventive measures. Document findings, actions, and outcomes.

When a Windows PC is configured to obtain an IP address automatically, the PC will try to obtain an IP address from a DHCP server. When the PC cannot contact a DHCP server, Windows will automatically assign an address belonging to the 169.254.0.0/16 range.

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.

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.

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.

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

A Trojan horse is malicious code that has been written specifically to look like a legitimate program. This is in contrast to a virus, which simply attaches itself to an actual legitimate program. Viruses require manual intervention from a user to spread from one system to another, while a worm is able to spread automatically between systems by exploiting vulnerabilities on those devices.

Reconnaissance is a type of attack where the intruder is looking for wireless network vulnerabilities.

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

he 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.

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.