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Networking Fundamentals · Intermediate

Point-to-Point Subnet

A subnet sized for exactly two devices, traditionally a /30 and now often a /31 in IPv4 or /127 in IPv6.

Definition

A /30 provides four addresses with two usable hosts. RFC 3021 allows /31 on point-to-point links, using both addresses with no network or broadcast address, which saves address space. RFC 6164 recommends /127 for IPv6 inter-router links.

Example

A WAN link might use 10.255.0.0/31, with 10.255.0.0 on one router and 10.255.0.1 on the other.

Exam tip

/30 = 2 usable hosts; /31 = 2 usable with no broadcast; /32 = single host route.

Related terms