CCNA 3 v7 Modules 3 – 5: Network Security Test Online

Hint

Cybercriminals are commonly motivated by money. Hackers are known to hack for status. Cyberterrorists are motivated to commit cybercrimes for religious or political reasons.

Hint

Hackers are categorized by motivating factors. Hacktivists are motivated by protesting political and social issues.

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A ping sweep is a tool that is used during a reconnaissance attack. Other tools that might be used during this type of attack include a ping sweep, port scan, or Internet information query. A reconnaissance attack is used to gather information about a particular network, usually in preparation for another type of network attack.

Hint

In a DoS or denial-of-service attack, the goal of the attacker is to prevent legitimate users from accessing network services.

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Integrity is ensured by implementing either MD5 or SHA hash generating algorithms. Many modern networks ensure authentication with protocols, such as HMAC. Data confidentiality is ensured through symmetric encryption algorithms, including DES, 3DES, and AES. Data confidentiality can also be ensured using asymmetric algorithms, including RSA and PKI.​

Hint

When an asymmetric algorithm is used, public and private keys are used for the encryption. Either key can be used for encryption, but the complementary matched key must be used for the decryption. For example if the public key is used for encryption, then the private key must be used for the decryption.

Hint

The permit 192.168.10.0 0.0.0.127 command ignores bit positions 1 through 7, which means that addresses 192.168.10.0 through 192.168.10.127 are allowed through. The two ACEs of permit 192.168.10.0 0.0.0.63 and permit 192.168.10.64 0.0.0.63 allow the same address range through the router.

Hint

Extended access lists commonly filter on source and destination IPv4 addresses and TCP or UDP port numbers. Additional filtering can be provided for protocol types.

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The two types of ACLs are standard and extended. Both types can be named or numbered, but extended ACLs offer greater flexibility.

Hint

Named ACL ACEs can be removed using the no command followed by the sequence number.

Hint

The R1(config)# no access-list <access-list number> command removes the ACL from the running-config immediately. However, to disable an ACL on an interface, the command R1(config-if)# no ip access-group should be entered.

Hint

When verifying an ACL, the statements are always listed in a sequential order. Even though there is an explicit permit for the traffic that is sourced from network 172.31.1.0 /24, it is being denied due to the previously implemented ACE of CiscoVille(config)# access-list 9 deny 172.31.0.0 0.0.255.255. The sequence of the ACEs must be modified to permit the specific traffic that is sourced from network 172.31.1.0 /24 and then to deny 172.31.0.0 /16.

Hint

To permit or deny one specific IP address, either the wildcard mask 0.0.0.0 (used after the IP address) or the wildcard mask keyword host (used before the IP address) can be used.

Hint

Standard access lists only filter on the source IP address. In the design, the packets would be coming from the 192.168.10.96/27 network (the R2 G0/0 network). The correct ACL is access-list 1 permit 192.168.10.96 0.0.0.31.

Hint

To deny traffic from the 172.16.0.0/16 network, the access-list 95 deny 172.16.0.0 0.0.255.255 command is used. To permit all other traffic, the access-list 95 permit any statement is added.

Hint

Because of the implicit deny at the end of all ACLs, the access-list 1 permit any command must be included to ensure that only traffic from the 172.16.4.0/24 subnet is blocked and that all other traffic is allowed.​

Hint

The only filtering criteria specified for a standard access list is the source IPv4 address. The wild card mask is written to identify what parts of the address to match, with a 0 bit, and what parts of the address should be ignored, which a 1 bit. The router will parse the ACE entries from lowest sequence number to highest. If an ACE must be added to an existing access list, the sequence number should be specified so that the ACE is in the correct place during the ACL evaluation process.

Hint

In an extended ACL, the first address is the source IP address and the second one is the destination IP address. TCP port number 22 is a well-known port number reserved for SSH connections. Telnet connections use TCP port number 23.

Hint

ACL entry 10 in MyACL matches any Telnet packets between host 10.35.80.22 and 10.23.77.101. No matches have occurred on this ACE as evidenced by the lack of a “(xxx matches)” ACE. The deny ip any any ACE is not required because there is an implicit deny ACE added to every access control list. When no matches exist for an ACL, it only means that no traffic has matched the conditions that exist for that particular line. The ACL is monitoring traffic that matches three specific hosts going to very specific destination devices. All other traffic is not permitted by the implicit deny ip any any ACE.

Hint

An extended ACL is placed as close to the source of the traffic as possible. In this case.it is placed in an inbound direction on interface fa0/0 on R2 for traffic entering the router from host with the IP address192.168.1.1 bound for the server with the IP address192.168.2.1.

Hint

The first ACE allows the 192.168.10.1 device to do any TCP/IP-based transactions with any other destination. The second ACE stops devices on the 192.168.10.0/24 network from issuing any pings to any other location. Everything else is permitted by the third ACE. Therefore, a Telnet/SSH session or ping reply is allowed from a device on the 192.168.10.0/24 network.

Hint

In a TCP SYN flood attack, the attacker sends to the target host a continuous flood of TCP SYN session requests with a spoofed source IP address. The target host responds with a TCP-SYN-ACK to each of the SYN session requests and waits for a TCP ACK that will never arrive. Eventually the target is overwhelmed with half-open TCP connections.

Hint

A cybercriminal could set up a rogue DHCP server that provides one or more of the following:

• Wrong default gateway that is used to create a man-in-the-middle attack and allow the attacker to intercept data
• Wrong DNS server that results in the user being sent to a malicious website
• Invalid default gateway IP address that results in a denial of service attack on the DHCP client

Hint

Any traffic that does not match one of the statements in an ACL has the implicit deny applied to it, which means the traffic is dropped.

Hint

A standard access list is commonly placed as close to the destination network as possible because access control expressions in a standard ACL do not include information about the destination network. The destination in this example is printer VLAN 12 which has router R1 Gigabit subinterface 0/1/.12 as its gateway. A sample standard ACL that only allows printing from data VLAN 10 (192.168.10.0/24), for example, and no other VLAN would be as follows:

R1(config)# access-list 1 permit 192.168.10.0 0.0.0.255
R1(config)# access-list 1 deny any
R1(config)# interface gigabitethernet 0/1.12
R1(config-if)# ip access-group 1 out

Hint

A standard IPv4 ACL can filter traffic based on source IP addresses only. Unlike an extended ACL, it cannot filter traffic based on Layer 4 ports. However, both standard and extended ACLs can be identified with either a number or a name, and both are configured in global configuration mode.

Hint

After the editing, the final configuration is as follows: Router# show access-lists Extended IP access list 101 5 permit tcp any any eq ssh 10 deny tcp any any 20 deny udp any any 30 permit icmp any any So, only SSH packets and ICMP packets will be permitted.​

Hint

For an extended ACL to meet these requirements the following need to be included in the access control entries:

• identification number in the range 100-199 or 2000-2699
• permit or deny parameter
• protocol
• source address and wildcard
• destination address and wildcard
• port number or name

Hint

Standard ACLs permit or deny packets based only on the source IPv4 address. Because all traffic types are permitted or denied, standard ACLs should be located as close to the destination as possible. Extended ACLs permit or deny packets based on the source IPv4 address and destination IPv4 address, protocol type, source and destination TCP or UDP ports and more. Because the filtering of extended ACLs is so specific, extended ACLs should be located as close as possible to the source of the traffic to be filtered. Undesirable traffic is denied close to the source network without crossing the network infrastructure.

Hint

Internal threats can be intentional or accidental and cause greater damage than external threats because the internal user has direct access to the internal corporate network and corporate data.

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Social engineering attempts to gain the confidence of an employee and convince that person to divulge confidential and sensitive information, such as usernames and passwords. DDoS attacks, spam, and keylogging are all examples of software based security threats, not social engineering.

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Zombies are infected computers that make up a botnet. The zombies are used to deploy a distributed denial of service (DDoS) attack.

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The man-in-the-middle attack is a common IP-related attack where threat actors position themselves between a source and destination to transparently monitor, capture, and control the communication.

Hint

The host keyword is used when using a specific device IP address in an ACL. For example, the deny host 192.168.5.5 command is the same is the deny 192.168.5.5 0.0.0.0 command. The any keyword is used to allow any mask through that meets the criteria. For example, the permit any command is the same as permit 0.0.0.0 255.255.255.255 command.

Hint

With an inbound ACL, incoming packets are processed before they are routed. With an outbound ACL, packets are first routed to the outbound interface, then they are processed. Thus processing inbound is more efficient from the router perspective. The structure, filtering methods, and limitations (on an interface, only one inbound and one outbound ACL can be configured) are the same for both types of ACLs.

Hint

Both named and numbered ACLs have an implicit deny ACE at the end of the list. This implicit deny blocks all traffic.

Hint

– Standard ACLs permit or deny packets based only on the source IPv4 address. Because all traffic types are permitted or denied, standard ACLs should be located as close to the destination as possible. – Extended ACLs permit or deny packets based on the source IPv4 address and destination IPv4 address, protocol type, source and destination TCP or UDP ports and more. Because the filtering of extended ACLs is so specific, extended ACLs should be located as close as possible to the source of the traffic to be filtered. Undesirable traffic is denied close to the source network without crossing the network infrastructure.

Hint

This access list must be an extended ACL in order to filter on specific source and destination host addresses. Commonly, the best place for an extended ACL is closest to the source, which is H1. Traffic from H1 travels into the switch, then out of the switch into the R1 Gi0/0 interface. This Gi0/0 interface would be the best location for this type of extended ACL. The ACL would be applied on the inbound interface since the packets from H1 would be coming into the R1 router.