Final answer:
To secure Telnet access to a router and restrict it to the corporate network, apply the appropriate ACL that reflects the proper subnet range. The ideal ACL entry should match the corporate network's assigned IP range and utilizes the correct wildcard mask.
Step-by-step explanation:
To control Telnet access to a router and allow only access from within the corporate network, you would use an access control list (ACL) applied to the virtual terminal (VTY) lines. An ACL will specify which IP addresses are allowed to make remote management connections to the router. When creating an ACL for this purpose, you need to include the corporate network's subnet range. Assuming the corporate network resides within certain IP ranges, one would select the proper permit statement that reflects this range.
Among the options provided, the best choice would depend on the actual subnet utilized by the corporate network. As an example:
- If the corporate network uses the IP range 172.16.0.0 to 172.31.255.255, you would use Access-list 1 permit 172.16.0.0 0.15.255.255.
- If the corporate network is within the 192.168.0.0 to 192.168.255.255 subnet, then you would use Access-list 1 permit 192.168.0.0 0.0.255.255.
- Alternatively, if the subnet is 10.0.0.0 to 10.255.255.255, the correct line is Access-list 1 permit 10.0.0.0 0.255.255.255.
The correct wildcard mask following each IP address defines the range of IP addresses included in that subnet and should correspond accurately to the network's actual subnetting scheme being used by the corporate network.