An engineer must configure a /30 subnet between two routes.
Which usable IP address and subnet mask combination meets this criteria?
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A. B. C. D.D.
To configure a /30 subnet between two routers, we need to use a subnet mask of 255.255.255.252. This subnet mask provides four IP addresses, of which two are usable.
The correct answer is A: interface e0/0 description to XX-AXXX:XXXXX ip address 10.2.1.3 255.255.255.252.
This IP address is part of the 10.0.0.0/8 private IP address range, which is commonly used for internal networks. The subnet mask of 255.255.255.252 provides four IP addresses in total: 10.2.1.0, 10.2.1.1, 10.2.1.2, and 10.2.1.3. However, only the first and last addresses in the range are not usable, which means that the usable IP addresses for this subnet are 10.2.1.1 and 10.2.1.2.
Option B (192.168.1.1 255.255.255.248) uses a /29 subnet mask, which provides eight IP addresses. This subnet mask is too large for a point-to-point link between two routers.
Option C (172.16.1.4 255.255.255.248) uses a private IP address range and the correct subnet mask, but the usable IP addresses are 172.16.1.5 and 172.16.1.6, not 172.16.1.3 and 172.16.1.4.
Option D (209.165.201.2 225.255.255.252) uses an incorrect subnet mask of 225.255.255.252. This is not a valid subnet mask and will not work for this configuration.
Therefore, the correct answer is A.