A/31 subnetin IPv4 provides exactlytwo IP addresses(e.g., 192.168.1.0/31 → usable: 192.168.1.0 and 192.168.1.1). Traditionally, these would represent anetwork address and a broadcast address, butRFC 3021redefines /31 subnets forpoint-to-point links, such as router-to-router connections.
In a /31 subnet:
Broadcast address is not used.
Both IPs are treated as usable host addresses.
It'sideal for point-to-point links, saving address space.
This is widely supported andstandardized in Nokia IP and routing platforms.
[Reference:, Nokia IP Fundamentals Guide – Subnetting Techniques, RFC 3021 – "Using 31-Bit Prefixes on IPv4 Point-to-Point Links", ===========]
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