In the network shown in the figure below, host A logs in to router A through Telnet, and then obtains the configuration file of router B through FTP on the remote interface. How many TCP connections exist on router A at this time?

• A.1
• B.4
• C.3
• D.2

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Which of the following descriptions about firewalls is wrong?

• A.The firewall cannot achieve network address translation
• B.Firewall can realize access control between different networks
• C.Firewall can realize user identity authentication
• D.Firewall can isolate networks with different security levels

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Which extension headers are supported by IPv6 packets? (Multiple choice)

• A.Hop-by-hop option extension header
• B.Fragmentation extension header
• C.VLAN extension header
• D.Destination option extension header

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In the network shown in the figure, which of the following configurations can realize that host A can access the Internet, but host B can not? (Multiple Choice)

• A.acl number 2000 rule 5 deny source 100.0.12.0 0.0.0.255 rule 10 permit source 100.0.13.0 0.0.0.255 # Interface GigabitEthernet0/0/3 traffic-filter outbound ac1 2000 #
• B.acl number 2000 rule 5 permit source 100.0.12.0 0.0.0.255 rule 10 deny source 100.0.13.0 0.0.0.255 # Interface GigabitEthernet0/0/3 traffic-filter outbound ac1 2000 #
• C.acl number 2000 rule 5 permit source 100.0.12.0 0.0.0.255 rule 10 deny # Interface GigabitEthernet0/0/3 traffic-filter outbound ac1 2000 #
• D.acl number 2000 rule 5 deny source 100.0.12.0 0.0.0.255 rule 10 permit # Interface GigabitEthernet0/0/3 traffic-filter outbound ac1 2000 #

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By default, network devices running SNMPv2c protocol use which of the following port numbers to send trap messages to the network management system?

• A.161
• B.162
• C.6
• D.17

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