CCNA 2 Chapter 9 v5.0 answers
1.
What two functions describe uses of an access control list? (Choose two.)
ACLs assist the router in determining the best path to a destination.
Standard ACLs can restrict access to specific applications and ports.
ACLs provide a basic level of security for network access.
ACLs can permit or deny traffic based upon the MAC address originating on the router.
ACLs can control which areas a host can access on a network.
2.
What are two possible uses of access control lists in an enterprise network? (Choose two.)
limiting debug outputs
reducing the processing load on routers
allowing Layer 2 traffic to be filtered by a router
controlling virtual terminal access to routers
controlling the physical status of router interfaces
3.
Which two characteristics are shared by both standard and extended ACLs? (Choose two.)
Both kinds of ACLs can filter based on protocol type.
Both can permit or deny specific services by port number.
Both include an implicit deny as a final ACE.
Both filter packets for a specific destination host IP address.
Both can be created by using either a descriptive name or number.
Standard ACLs filter traffic based solely on a specified source IP address. Extended ACLs can filter by source or destination, protocol, or port. Both standard and extended ACLs contain an implicit deny as a final ACE. Standard and extended ACLs can be identified by either names or numbers.
4.
Which statement describes a characteristic of standard IPv4 ACLs?
They are configured in the interface configuration mode.
They filter traffic based on source IP addresses only.
They can be created with a number but not with a name.
They can be configured to filter traffic based on both source IP addresses and source ports.
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.
5.
A network administrator needs to configure a standard ACL so that only the workstation of the administrator with the IP address 192.168.15.23 can access the virtual terminal of the main router. Which two configuration commands can achieve the task? (Choose two.)
Router1(config)# access-list 10 permit host 192.168.15.23
Router1(config)# access-list 10 permit 192.168.15.23 0.0.0.0
Router1(config)# access-list 10 permit 192.168.15.23 0.0.0.255
Router1(config)# access-list 10 permit 192.168.15.23 255.255.255.0
Router1(config)# access-list 10 permit 192.168.15.23 255.255.255.255
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.
6.
Which IPv4 address range covers all IP addresses that match the ACL filter specified by 172.16.2.0 with wildcard mask 0.0.1.255?
172.16.2.0 to 172.16.2.255
172.16.2.1 to 172.16.3.254
172.16.2.0 to 172.16.3.255
172.16.2.1 to 172.16.255.255
The wildcard mask 0.0.1.255 means the first 23 bits are matched and the last 9 bits are ignored. That is, a matching IP address should be from 172.16.2.0 to 172.16.3.255 (where last 9 bits are from all 0s to all 1s and any value between).
7.
If a router has two interfaces and is routing both IPv4 and IPv6 traffic, how many ACLs could be created and applied to it?
4
6
8
12
16
In calculating how many ACLs can be configured, use the rule of “three Ps”: one ACL per protocol, per direction, per interface. In this case, 2 interfaces x 2 protocols x 2 directions yields 8 possible ACLs.
8.
Which three statements are generally considered to be best practices in the placement of ACLs? (Choose three.)
Place standard ACLs close to the source IP address of the traffic.
Place extended ACLs close to the destination IP address of the traffic.
Filter unwanted traffic before it travels onto a low-bandwidth link.
Place extended ACLs close to the source IP address of the traffic.
Place standard ACLs close to the destination IP address of the traffic.
For every inbound ACL placed on an interface, there should be a matching outbound ACL.
Extended ACLs should be placed as close as possible to the source IP address, so that traffic that needs to be filtered does not cross the network and use network resources. Because standard ACLs do not specify a destination address, they should be placed as close to the destination as possible. Placing a standard ACL close to the source may have the effect of filtering all traffic, and limiting services to other hosts. Filtering unwanted traffic before it enters low-bandwidth links preserves bandwidth and supports network functionality. Decisions on placing ACLs inbound or outbound are dependent on the requirements to be met.
9.
Refer to the exhibit. A router has an existing ACL that permits all traffic from the 172.16.0.0 network. The administrator attempts to add a new ACE to the ACL that denies packets from host 172.16.0.1 and receives the error message that is shown in the exhibit. What action can the administrator take to block packets from host 172.16.0.1 while still permitting all other traffic from the 172.16.0.0 network?
chapter9-3
Manually add the new deny ACE with a sequence number of 5.
Manually add the new deny ACE with a sequence number of 15.
Create a second access list denying the host and apply it to the same interface.
Add a deny any any ACE to access-list 1.
Because the new deny ACE is a host address that falls within the existing 172.16.0.0 network that is permitted, the router rejects the command and displays an error message. For the new deny ACE to take effect, it must be manually configured by the administrator with a sequence number that is less than 10.
10.
An administrator has configured an access list on R1 to allow SSH administrative access from host 172.16.1.100. Which command correctly applies the ACL?
R1(config-if)# ip access-group 1 in
R1(config-if)# ip access-group 1 out
R1(config-line)# access-class 1 in
R1(config-line)# access-class 1 out
Administrative access over SSH to the router is through the vty lines. Therefore, the ACL must be applied to those lines in the inbound direction. This is accomplished by entering line configuration mode and issuing the access-class command.
11.
Refer to the exhibit. The network administrator that has the IP address of 10.0.70.23/25 needs to have access to the corporate FTP server (10.0.54.5/28). The FTP server is also a web server that is accessible to all internal employees on networks within the 10.x.x.x address. No other traffic should be allowed to this server. Which extended ACL would be used to filter this traffic, and how would this ACL be applied? (Choose two.)
12.
Consider the following access list that allows IP phone configuration file transfers from a particular host to a TFTP server:
To modify an extended numbered ACL remove the ACL from the interface. Copy the ACL into a text document. Delete the ACL from the router. Modify the ACL within the text document and re-enter the ACL into the router and apply it to the interface.
13.
Which statement describes a difference between the operation of inbound and outbound ACLs?
In contrast to outbound ALCs, inbound ACLs can be used to filter packets with multiple criteria.
Inbound ACLs can be used in both routers and switches but outbound ACLs can be used only on routers.
Inbound ACLs are processed before the packets are routed while outbound ACLs are processed after the routing is completed.
On a network interface, more than one inbound ACL can be configured but only one outbound ACL can be configured.
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.
14.
Which feature is unique to IPv6 ACLs when compared to those of IPv4 ACLs?
the use of wildcard masks
an implicit deny any any ACE
the use of named ACL entries
an implicit permit of neighbor discovery packets
One of the major differences between IPv6 and IPv4 ACLs are two implicit permit ACEs at the end of any IPv6 ACL. These two permit ACEs allow neighbor discovery operations to function on the router interface.
15.
Which three statements describe ACL processing of packets? (Choose three.)
An implicit deny any rejects any packet that does not match any ACE.
A packet can either be rejected or forwarded as directed by the ACE that is matched.
A packet that has been denied by one ACE can be permitted by a subsequent ACE.
A packet that does not match the conditions of any ACE will be forwarded by default.
Each statement is checked only until a match is detected or until the end of the ACE list.
Each packet is compared to the conditions of every ACE in the ACL before a forwarding decision is made.
16.
Which three implicit access control entries are automatically added to the end of an IPv6 ACL? (Choose three.)
deny ip any any
deny ipv6 any any
permit ipv6 any any
deny icmp any any
permit icmp any any nd-ns
permit icmp any any nd-na
All IPv6 ACLs automatically include two implicit permit statements; permit icmp any any nd-ns and permit icmp any any nd-na. These statements allow the router interface to perform neighbor discovery operations. There is also an implicit deny ipv6 any any automatically included at the very end of any IPv6 ACL that blocks all IPv6 packets not otherwise permitted.
17.
What is the only type of ACL available for IPv6?
named standard
named extended
numbered standard
numbered extended
Unlike IPv4, IPv6 has only one type of access list and that is the named extended access list.
18.
Which IPv6 ACL command entry will permit traffic from any host to an SMTP server on network 2001:DB8:10:10::/64?
permit tcp any host 2001:DB8:10:10::100 eq 25
permit tcp host 2001:DB8:10:10::100 any eq 25
permit tcp any host 2001:DB8:10:10::100 eq 23
permit tcp host 2001:DB8:10:10::100 any eq 23
The IPv6 access list statement, permit tcp any host 2001:DB8:10:10::100 eq 25, will allow IPv6 packets from any host to the SMTP server at 2001:DB8:10:10::100. The source of the packet is listed first in the ACL, which in this case is any source, and the destination is listed second, in this case the IPv6 address of the SMTP server. The port number is last in the statement, port 25, which is the well-known port for SMTP.
19.
Refer to the exhibit. The IPv6 access list LIMITED_ACCESS is applied on the S0/0/0 interface of R1 in the inbound direction. Which IPv6 packets from the ISP will be dropped by the ACL on R1?
chapter9-1
HTTPS packets to PC1
ICMPv6 packets that are destined to PC1
packets that are destined to PC1 on port 80
neighbor advertisements that are received from the ISP router
The access list LIMITED_ACCESS will block ICMPv6 packets from the ISP. Both port 80, HTTP traffic, and port 443, HTTPS traffic, are explicitly permitted by the ACL. The neighbor advertisements from the ISP router are implicitly permitted by the implicit permit icmp any any nd-na statement at the end of all IPv6 ACLs.
20.
Question as presented:
Converting the wildcard mask 0.0.3.255 to binary and subtracting it from 255.255.255.255 yields a subnet mask of 255.255.252.0.
Using the host parameter in a wildcard mask requires that all bits match the given address.
192.168.15.65 is the first valid host address in a subnetwork beginning with the subnetwork address 192.168.15.64. The subnet mask contains 4 host bits, yielding subnets with 16 addresses.
192.168.15.144 is a valid subnetwork address in a similar subnetwork. Change the wildcard mask 0.0.0.15 to binary and subtract it from 255.255.255.255, and the resulting subnet mask is 255.255.255.240.
192.168.3.64 is a subnetwork address in a subnet with 8 addresses. Convert 0.0.0.7 to binary and subtract it from 255.255.255.255, and the resulting subnet mask is 255.255.255.248. That mask contains 3 host bits, and yields 8 addresses.
21.
Open the PT Activity. Perform the tasks in the activity instructions and then answer the question.
Why is the ACL not working?
No ACL is needed for this scenario.
The ACL is applied in the wrong direction.
The ACL is missing a deny ip any any ACE.
The ACL is applied to the wrong interface.
The access-list 105 command or commands are incorrect.
The ACL is currently applied to the unused Fa0/0 interface. The server is attached to the same network to which the R1 Fa0/1 interface is attached. The ACL should be applied to this interface to protect the server
What two functions describe uses of an access control list? (Choose two.)
ACLs assist the router in determining the best path to a destination.
Standard ACLs can restrict access to specific applications and ports.
ACLs provide a basic level of security for network access.
ACLs can permit or deny traffic based upon the MAC address originating on the router.
ACLs can control which areas a host can access on a network.
2.
What are two possible uses of access control lists in an enterprise network? (Choose two.)
limiting debug outputs
reducing the processing load on routers
allowing Layer 2 traffic to be filtered by a router
controlling virtual terminal access to routers
controlling the physical status of router interfaces
3.
Which two characteristics are shared by both standard and extended ACLs? (Choose two.)
Both kinds of ACLs can filter based on protocol type.
Both can permit or deny specific services by port number.
Both include an implicit deny as a final ACE.
Both filter packets for a specific destination host IP address.
Both can be created by using either a descriptive name or number.
Standard ACLs filter traffic based solely on a specified source IP address. Extended ACLs can filter by source or destination, protocol, or port. Both standard and extended ACLs contain an implicit deny as a final ACE. Standard and extended ACLs can be identified by either names or numbers.
4.
Which statement describes a characteristic of standard IPv4 ACLs?
They are configured in the interface configuration mode.
They filter traffic based on source IP addresses only.
They can be created with a number but not with a name.
They can be configured to filter traffic based on both source IP addresses and source ports.
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.
5.
A network administrator needs to configure a standard ACL so that only the workstation of the administrator with the IP address 192.168.15.23 can access the virtual terminal of the main router. Which two configuration commands can achieve the task? (Choose two.)
Router1(config)# access-list 10 permit host 192.168.15.23
Router1(config)# access-list 10 permit 192.168.15.23 0.0.0.0
Router1(config)# access-list 10 permit 192.168.15.23 0.0.0.255
Router1(config)# access-list 10 permit 192.168.15.23 255.255.255.0
Router1(config)# access-list 10 permit 192.168.15.23 255.255.255.255
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.
6.
Which IPv4 address range covers all IP addresses that match the ACL filter specified by 172.16.2.0 with wildcard mask 0.0.1.255?
172.16.2.0 to 172.16.2.255
172.16.2.1 to 172.16.3.254
172.16.2.0 to 172.16.3.255
172.16.2.1 to 172.16.255.255
The wildcard mask 0.0.1.255 means the first 23 bits are matched and the last 9 bits are ignored. That is, a matching IP address should be from 172.16.2.0 to 172.16.3.255 (where last 9 bits are from all 0s to all 1s and any value between).
7.
If a router has two interfaces and is routing both IPv4 and IPv6 traffic, how many ACLs could be created and applied to it?
4
6
8
12
16
In calculating how many ACLs can be configured, use the rule of “three Ps”: one ACL per protocol, per direction, per interface. In this case, 2 interfaces x 2 protocols x 2 directions yields 8 possible ACLs.
8.
Which three statements are generally considered to be best practices in the placement of ACLs? (Choose three.)
Place standard ACLs close to the source IP address of the traffic.
Place extended ACLs close to the destination IP address of the traffic.
Filter unwanted traffic before it travels onto a low-bandwidth link.
Place extended ACLs close to the source IP address of the traffic.
Place standard ACLs close to the destination IP address of the traffic.
For every inbound ACL placed on an interface, there should be a matching outbound ACL.
Extended ACLs should be placed as close as possible to the source IP address, so that traffic that needs to be filtered does not cross the network and use network resources. Because standard ACLs do not specify a destination address, they should be placed as close to the destination as possible. Placing a standard ACL close to the source may have the effect of filtering all traffic, and limiting services to other hosts. Filtering unwanted traffic before it enters low-bandwidth links preserves bandwidth and supports network functionality. Decisions on placing ACLs inbound or outbound are dependent on the requirements to be met.
9.
Refer to the exhibit. A router has an existing ACL that permits all traffic from the 172.16.0.0 network. The administrator attempts to add a new ACE to the ACL that denies packets from host 172.16.0.1 and receives the error message that is shown in the exhibit. What action can the administrator take to block packets from host 172.16.0.1 while still permitting all other traffic from the 172.16.0.0 network?
chapter9-3
Manually add the new deny ACE with a sequence number of 5.
Manually add the new deny ACE with a sequence number of 15.
Create a second access list denying the host and apply it to the same interface.
Add a deny any any ACE to access-list 1.
Because the new deny ACE is a host address that falls within the existing 172.16.0.0 network that is permitted, the router rejects the command and displays an error message. For the new deny ACE to take effect, it must be manually configured by the administrator with a sequence number that is less than 10.
10.
An administrator has configured an access list on R1 to allow SSH administrative access from host 172.16.1.100. Which command correctly applies the ACL?
R1(config-if)# ip access-group 1 in
R1(config-if)# ip access-group 1 out
R1(config-line)# access-class 1 in
R1(config-line)# access-class 1 out
Administrative access over SSH to the router is through the vty lines. Therefore, the ACL must be applied to those lines in the inbound direction. This is accomplished by entering line configuration mode and issuing the access-class command.
11.
Refer to the exhibit. The network administrator that has the IP address of 10.0.70.23/25 needs to have access to the corporate FTP server (10.0.54.5/28). The FTP server is also a web server that is accessible to all internal employees on networks within the 10.x.x.x address. No other traffic should be allowed to this server. Which extended ACL would be used to filter this traffic, and how would this ACL be applied? (Choose two.)
12.
Consider the following access list that allows IP phone configuration file transfers from a particular host to a TFTP server:
To modify an extended numbered ACL remove the ACL from the interface. Copy the ACL into a text document. Delete the ACL from the router. Modify the ACL within the text document and re-enter the ACL into the router and apply it to the interface.
13.
Which statement describes a difference between the operation of inbound and outbound ACLs?
In contrast to outbound ALCs, inbound ACLs can be used to filter packets with multiple criteria.
Inbound ACLs can be used in both routers and switches but outbound ACLs can be used only on routers.
Inbound ACLs are processed before the packets are routed while outbound ACLs are processed after the routing is completed.
On a network interface, more than one inbound ACL can be configured but only one outbound ACL can be configured.
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.
14.
Which feature is unique to IPv6 ACLs when compared to those of IPv4 ACLs?
the use of wildcard masks
an implicit deny any any ACE
the use of named ACL entries
an implicit permit of neighbor discovery packets
One of the major differences between IPv6 and IPv4 ACLs are two implicit permit ACEs at the end of any IPv6 ACL. These two permit ACEs allow neighbor discovery operations to function on the router interface.
15.
Which three statements describe ACL processing of packets? (Choose three.)
An implicit deny any rejects any packet that does not match any ACE.
A packet can either be rejected or forwarded as directed by the ACE that is matched.
A packet that has been denied by one ACE can be permitted by a subsequent ACE.
A packet that does not match the conditions of any ACE will be forwarded by default.
Each statement is checked only until a match is detected or until the end of the ACE list.
Each packet is compared to the conditions of every ACE in the ACL before a forwarding decision is made.
16.
Which three implicit access control entries are automatically added to the end of an IPv6 ACL? (Choose three.)
deny ip any any
deny ipv6 any any
permit ipv6 any any
deny icmp any any
permit icmp any any nd-ns
permit icmp any any nd-na
All IPv6 ACLs automatically include two implicit permit statements; permit icmp any any nd-ns and permit icmp any any nd-na. These statements allow the router interface to perform neighbor discovery operations. There is also an implicit deny ipv6 any any automatically included at the very end of any IPv6 ACL that blocks all IPv6 packets not otherwise permitted.
17.
What is the only type of ACL available for IPv6?
named standard
named extended
numbered standard
numbered extended
Unlike IPv4, IPv6 has only one type of access list and that is the named extended access list.
18.
Which IPv6 ACL command entry will permit traffic from any host to an SMTP server on network 2001:DB8:10:10::/64?
permit tcp any host 2001:DB8:10:10::100 eq 25
permit tcp host 2001:DB8:10:10::100 any eq 25
permit tcp any host 2001:DB8:10:10::100 eq 23
permit tcp host 2001:DB8:10:10::100 any eq 23
The IPv6 access list statement, permit tcp any host 2001:DB8:10:10::100 eq 25, will allow IPv6 packets from any host to the SMTP server at 2001:DB8:10:10::100. The source of the packet is listed first in the ACL, which in this case is any source, and the destination is listed second, in this case the IPv6 address of the SMTP server. The port number is last in the statement, port 25, which is the well-known port for SMTP.
19.
Refer to the exhibit. The IPv6 access list LIMITED_ACCESS is applied on the S0/0/0 interface of R1 in the inbound direction. Which IPv6 packets from the ISP will be dropped by the ACL on R1?
chapter9-1
HTTPS packets to PC1
ICMPv6 packets that are destined to PC1
packets that are destined to PC1 on port 80
neighbor advertisements that are received from the ISP router
The access list LIMITED_ACCESS will block ICMPv6 packets from the ISP. Both port 80, HTTP traffic, and port 443, HTTPS traffic, are explicitly permitted by the ACL. The neighbor advertisements from the ISP router are implicitly permitted by the implicit permit icmp any any nd-na statement at the end of all IPv6 ACLs.
20.
Question as presented:
Converting the wildcard mask 0.0.3.255 to binary and subtracting it from 255.255.255.255 yields a subnet mask of 255.255.252.0.
Using the host parameter in a wildcard mask requires that all bits match the given address.
192.168.15.65 is the first valid host address in a subnetwork beginning with the subnetwork address 192.168.15.64. The subnet mask contains 4 host bits, yielding subnets with 16 addresses.
192.168.15.144 is a valid subnetwork address in a similar subnetwork. Change the wildcard mask 0.0.0.15 to binary and subtract it from 255.255.255.255, and the resulting subnet mask is 255.255.255.240.
192.168.3.64 is a subnetwork address in a subnet with 8 addresses. Convert 0.0.0.7 to binary and subtract it from 255.255.255.255, and the resulting subnet mask is 255.255.255.248. That mask contains 3 host bits, and yields 8 addresses.
21.
Open the PT Activity. Perform the tasks in the activity instructions and then answer the question.
Why is the ACL not working?
No ACL is needed for this scenario.
The ACL is applied in the wrong direction.
The ACL is missing a deny ip any any ACE.
The ACL is applied to the wrong interface.
The access-list 105 command or commands are incorrect.
The ACL is currently applied to the unused Fa0/0 interface. The server is attached to the same network to which the R1 Fa0/1 interface is attached. The ACL should be applied to this interface to protect the server
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