Implementing Network Security (Version 2.0) – CCNA Security (IINS) Certification Practice Exam Online

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A virus is malicious code that is attached to legitimate programs or executable files. Most viruses require end user activation, can lie dormant for an extended period, and then activate at a specific time or date. In contrast, a worm executes arbitrary code and installs copies of itself in the memory of the infected computer. The main purpose of a worm is automatic replication to spread quickly across a network. A worm does not require a host program to run.

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Using an intrusion prevention system (IPS) and firewall can limit the information that can be discovered with a port scanner. Authentication, encryption, and passwords provide no protection from loss of information from port scanning.

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For security, all traffic between the administrator computer and the router should be encrypted by using HTTPS or SSH instead of HTTP or Telnet.

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When the login block-for command is implemented, it automatically invokes a one-second delay between login attempts. The login block-for command that is presented means that login will be disabled for 150 seconds, if more than 5 login failures occur within 60 seconds. These enhancements do not apply to console connections. When quiet mode is enabled, all login attempts are denied except for the hosts permitted in the ACL.

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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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A CLI view has no command hierarchy, and therefore, no higher or lower views. Deleting a superview does not delete the associated CLI views. Only a root view user can configure a new view and add or remove commands from the existing views.​

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The Cisco IOS Resilient Configuration feature allows a secure copy of the IOS and running configuration file to be stored locally on a router. If flash memory or NVRAM is inadvertently or maliciously erased, the router can be quickly restored using the stored files.

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Secure Copy Protocol (SCP) is used to securely copy IOS images and configuration files to a SCP server. To perform this, SCP will use SSH connections from users authenticated through AAA.

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Syslog levels range from 0 to 7:
Level 0 is Log_Emerg
Level 1 is Log_Alert
Level 2 is Log_Crit
Level 3 is Log_Err
Level 4 is Log_Warning
Level 5 is Log_Notice
Level 6 is Log_Info
Level 7 is Log_Debug

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The message shown is a level 5 Log_Notice and displays that a user with an IP address of 172.16.45.1 has configured this device remotely.

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Cisco Express Forwarding, traffic filtering with ACLs, and Cisco IOS firewall inspection are forwarding plane services that provide security. Management plane security includes these features:legal notification using a banner
secure password and login functions
secure NTP
secure SSH access
TCP intercept services

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The authentication component of AAA is established using username and password combinations, challenge and response questions, and token cards. The authorization component of AAA determines which resources the user can access and which operations the user is allowed to perform. The accounting and auditing component of AAA keeps track of how network resources are used.

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AAA authorization is implemented immediately after the user is authenticated against a specific AAA data source.

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When an AAA user is authenticated, RADIUS uses UDP port 1645 or 1812 for authentication and UDP port 1646 or 1813 for accounting. TACACS provides separate authorization and accounting services. When a RADIUS client is authenticated, it is also authorized. TACACS provides secure connectivity using TCP port 49. RADIUS hides passwords during transmission and does not encrypt the complete packet.​

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TACACS+ utilizes TCP port 49, provides authorization on a per-user or per-group basis, encrypts the entire packet, and does not provide compa​tibility with previous TACACS protocols.​

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RADIUS authentication supports the following features:RADIUS authentication and authorization as one process
Encrypts only the password
Utilizes UDP
Supports remote-access technologies, 802.1X, and Session Initiation Protocol (SIP)

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TACACS+ authentication includes the following attributes:
Separates authentication and authorization processes
Encrypts all communication, not just passwords
Utilizes TCP port 49

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RADIUS authentication and accounting utilize the following UDP port numbers:UDP port 1645 or 1812 for authentication
UDP port 1646 or 1813 for accounting
TACACS+ uses TCP port 49.

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An IPS is deployed in inline mode whereas an IDS is deployed in promiscuous mode. An effective deployment of IPS/IDS is to place an IPS right behind the border router to filter the traffic inbound to and outbound from the corporate internal network. IPS and IDS technologies can complement each other. Although an IDS will not stop an intrusion attack immediately, it can be used to validate IPS operation because the IDS can be configured for deeper packet inspection offline. This allows the IPS to focus on fewer but more critical traffic patterns inline. Placing IPS and IDS in the DMZ network will not protect the corporate internal network.

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To analyze network traffic passing through a switch, switched port analyzer (SPAN) can be used. SPAN can send a copy of traffic from one port to another port on the same switch where a network analyzer or monitoring device is connected. SPAN is not required for syslog or SNMP. SPAN is used to mirror traffic, while syslog and SNMP are configured to send data directly to the appropriate server.

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IPS signatures have three distinctive attributes:

• type
• trigger (alarm)
• action

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The alarms generated by an IPS can be classified into 4 types:A false positive occurs when an IPS generates an alarm on normal user traffic that should not have triggered an alarm.
A false negative occurs when an IPS fails to generate an alarm after processing attack traffic the IPS is configured to detect.
A true positive occurs when an IPS generates an alarm in response to known attack traffic.
A true negative occurs when normal network traffic does not generate an alarm.

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There are four IPS trigger types:
pattern-based detection
anomaly-based detection
policy-based detection
honeypot-based detection
Anomaly-based detection compares network activity to a predefined profile of what is considered normal activity.

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There are four IPS alarms:
False positive – occurs when normal traffic triggers an alarm
False negative – occurs when known malicious traffic that should trigger an alarm does not
True positive – occurs when traffic that is known to be malicious triggers an attack
True negative – occurs when normal traffic does not trigger an alarm

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There are four IPS alarms:
False positive – occurs when normal traffic triggers an alarm
False negative – occurs when known malicious traffic that should trigger an alarm does not
True positive – occurs when traffic that is known to be malicious triggers an attack
True negative – occurs when normal traffic does not trigger an alarm

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Alerts generated by an IPS should be monitored closely to ensure proper actions are taken against malicious attacks. IPS solutions incorporate two types of alerts, atomic alerts and summary alerts. Atomic alerts are generated every time a signature triggers. A summary alert is a single alert that indicates multiple occurrences of the same signature from the same source address or port. With a summary alter, the first detection of the attack triggers a normal alert. Subsequent detection of the same attack is counted until the end of the signature summary interval. When the length of time specified by the summary interval has elapsed, a summary alarm is sent, indicating the number of alarms that occurred during the time interval.

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The third step in implementing IOS IPS is to configure the Cisco IOS IPS public key that is located in the realm-cisco.pub.key.txt file. This public key is used to verify digital signature for the master signature file, and can be downloaded from cisco.com. To configure the IOS IPS crypto key, open the text file, and copy and paste the contents to the router at the global configuration prompt. Public/private key pairs for IPsec VPN and SSH server are generated using different methods.

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Cisco ESAs control outbound messages through data-loss prevention (DLP), email encryption, and optional integration with the RSA Enterprise Manager. This control helps ensure that the outbound messages comply with industry standards and are protected in transit.

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Cisco NAC is used in the Cisco Borderless Network Architecture to authenticate users and ensure user devices are compliant with security policies. The Cisco NAC Agent is optional agent software that runs on endpoints and performs deep inspection of the security profile of that device.

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The goal of both the Cisco NAC framework and the Cisco NAC Appliance is to ensure that only hosts that are authenticated and have their security posture examined and approved are permitted onto the network. They provide four important functions: authentication, authorization, and accounting; posture assessment (evaluating an incoming device against the security policies), quarantining of non-compliant systems, and remediation of noncompliant devices. They do not provide VPN connection or intrusion detection/prevention services.

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A MAC address (CAM) table overflow attack, buffer overflow, and MAC address spoofing can all be mitigated by configuring port security. A network administrator would typically not want to disable STP because it prevents Layer 2 loops. DTP is disabled to prevent VLAN hopping. Placing unused ports in an unused VLAN prevents unauthorized wired connectivity.

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Port security is the most effective method for preventing CAM table overflow attacks. Port security gives an administrator the ability to manually specify what MAC addresses should be seen on given switch ports. It provides a method for limiting the number of MAC addresses that can be dynamically learned over a switch port.

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Implementing switch port-security will assist in mitigating DoS attacks. In order to mitigate reconnaissance attacks, it is best to use strong authentication, a switched infrastructure, antisniffer software, and encryption.

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There are two methods for mitigating VLAN hopping attacks:

1. disabling automatic trunking negotiation on switchports
2. turning trunking off on all unused nontrunk switchport

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Root guard in conjunction with PortFast, and BPDU guard is used to prevent an STP manipulation attack.

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There are several recommended STP stability mechanisms to help mitigate STP manipulation attacks:

• PortFast – Used to immediately bring an interface configured as an access or trunk port to the forwarding state from a blocking state. Applied to all end-user ports.
• BPDU guard – Immediately error-disables a port that receives a BPDU. Applied to all end-user ports.
• Root guard – Prevents a switch from becoming the root switch. Applied to all ports where root switch should not be located.
• Loop guard – Detects unidirectional links to prevent alternate or root ports from becoming designated ports. Applied to all ports that are or can become non-designated.

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There are several recommended STP stability mechanisms to help mitigate STP manipulation attacks:
PortFast – used to immediately bring an interface configured as an access or trunk port to the forwarding state from a blocking state. Applied to all end-user ports.
BPDU guard – immediately error-disables a port that receives a BPDU. Applied to all end-user ports.The receipt of BPDUs may be part of an unauthorized attempt to add a switch to the network.
Root guard – prevents a switch from becoming the root switch. Applied to all ports where the root switch should not be located.
Loop guard – detects unidirectional links to prevent alternate or root ports from becoming designated ports. Applied to all ports that are or can become nondesignated.

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Symmetric algorithms use the same key, a secret key, to encrypt and decrypt data. This key must be pre-shared before communication can occur. Asymmetric algorithms require more processing power and overhead on the communicating devices because these keys can be long in order to avoid being hacked.

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The Diffie-Hellman (DH) algorithm is a modern key exchange method that allows the exchange of secret keys securely over an untrusted network.

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Asymmetric algorithms use two keys. if a public key encrypts the data, the matching private key decrypts the data. The opposite is also true. If a private key encrypts the data, the corresponding public key decrypts the data.

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Asymmetric algorithms use two keys. if a public key encrypts the data, the matching private key decrypts the data. The opposite is also true. If a private key encrypts the data, the corresponding public key decrypts the data.

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DES uses 56-bit keys. 3DES uses 56-bit keys, but encrypts three times. AES uses 128-bit keys. AES-256 uses 256-bit keys and is the strongest.

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As seen in the 8.4.1.1 Figure, an IPsec VPN connection creates two SAs: (1) at the completion of the IKE Phase 1 once the peers negotiate the IKE SA policy, and (2) at the end of IKE Phase 2 after the transform sets are negotiated.

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Establishing an IPsec tunnel involves five steps:

• Detection of interesting traffic defined by an ACL
• IKE Phase 1 in which peers negotiate ISAKMP SA policy
• IKE Phase 2 in which peers negotiate IPsec SA policy
• Creation of the IPsec tunnel
• Termination of the IPsec tunnel

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Establishing an IPsec tunnel involves five steps:

• detection of interesting traffic defined by an ACL
• IKE Phase 1 in which peers negotiate ISAKMP SA policy
• IKE Phase 2 in which peers negotiate IPsec SA policy
• Creation of the IPsec tunnel
• Termination of the IPsec tunnel

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The transform set is negotiated during Phase 2 of the IPsec VPN connection process. The purpose of the transform set is to define what encryption and authentication schemes can be used. The device doing the VPN initiation offers the acceptable transform sets in order of preference, in this case, ESP authentication using DES for encryption or ESP authentication using SHA-HMAC authentication and integrity for the data payload. Remember that ESP provides confidentiality with encryption and integrity with authentication. The ESP-DES-SHA is the name of the transform set. The parameters that follow (esp-des and esp-sha-hmac) are the specific types of encryption or authentication that is supported by the ASA for the VPN tunnel that uses this transform set.

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ASA devices have security levels assigned to each interface that are not part of a configured ACL. These security levels allow traffic from more secure interfaces, such as security level 100, to access less secure interfaces, such as level 0. By default, they allow traffic from more secure interfaces (higher security level) to access less secure interfaces (lower security level). Traffic from the less secure interfaces is blocked from accessing more secure interfaces.

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The Cisco IOS ACLs are configured with a wildcard mask and the Cisco ASA ACLs are configured with a subnet mask. Both devices use an implicit deny, top down sequential processing, and named or numbered ACLs.

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The differences between ASA devices and Cisco IOS routers include the following:
An ASA device configured with ACLs is configured with a subnet mask.
An ASA device supports interface security levels.
An ASA device configured with an ACL is always named.

ASA devices and Cisco IOS routers are similar in that they both support an implicit deny within an ACL.

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On an ASA, both the pool of addresses that will be used as inside global address and the range of internal private addresses that should be translated are configured through network objects.

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There are three configuration objects in the MPF; class maps, policy maps, and service policy. The class maps configuration object uses match criteria to identify interesting traffic.