/30 subnet: mask 255.255.255.252, 2 usable hosts

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Updated Oct 8, 2026

Examples

IP address / CIDR / netmask

IPv4 or IPv6, with or without a prefix — 10.0.0.0/8, 2001:db8::/48, or a dotted netmask like 192.168.1.0 255.255.255.0. A bare address means one host (/32 or /128).

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fig. 10 — subnet-calculator · networking /30 — 2 usable hosts

Result

IPv410.0.0.0/30

Usable hosts2

Usable range10.0.0.1 – 10.0.0.2

Total addresses4

Addressing

Network address: 10.0.0.0
Broadcast address: 10.0.0.3
Usable host range: 10.0.0.1 – 10.0.0.2

Masks

Netmask: 255.255.255.252
Wildcard maskInverse of the netmask — the match form Cisco ACLs and OSPF expect.: 0.0.0.3
Netmask (binary)The mask bit by bit — the 1s are the network part.: 11111111.11111111.11111111.11111100

Details

Address type: Private (RFC 1918)
Network (integer)The network address as a single 32-bit number, as scripts and databases store it.: 167 772 160

Check against CIDRs Split this subnet Convert this address

A /30 is netmask 255.255.255.252: 4 addresses, 2 usable hosts. It was the standard size for a router-to-router link for decades.

What /30 means

Two host bits remain, so the mask is 255.255.255.252 and the wildcard 0.0.0.3. Networks sit at multiples of 4.

2^2 = 4 addresses. The network and broadcast take two, so 2 remain: in 10.0.0.0/30 those are 10.0.0.1 and 10.0.0.2, with 10.0.0.3 as broadcast. A /30 is the smallest subnet where the usual "minus two" rule still produces usable hosts.

Point-to-point links

A WAN circuit, a GRE or IPsec tunnel, or a BGP session between two routers needs exactly two addresses, one per end. A /30 delivers that, at the price of half its addresses going to the network and broadcast entries a two-node link never uses.

RFC 3021 lets a /31 do the same job with no waste, and most modern routing platforms support it. A /30 is still the safe default when the far end is an older device, a firewall that rejects /31, or a provider whose provisioning only knows /30.

Planning link addresses

Teams usually reserve one /24 for links and slice it into 64 /30s (or 128 /31s). A /30 splits into two /31s; two aligned /30s make a /29.

Configuring a /30 link

One end takes 10.0.0.1, the other 10.0.0.2, both with mask 255.255.255.252. A convention such as lower address on the provider side makes troubleshooting faster, because anyone can tell which end they are looking at from the address alone.

Watch for typos that put the two ends in different /30s, for example .2 and .5. Each side then thinks the other is off-link, the interface stays up and the routing protocol never forms an adjacency.

Document each link with both addresses and the device names at each end. Link blocks are small and numerous, so an IPAM entry per /30 is what keeps two engineers from handing out the same one on different sides of the network.

FAQ

Questions, answered.

Tap a question to expand the answer.

Why use a /30 instead of a /31?

Compatibility. Every IPv4 stack handles a /30, while /31 needs RFC 3021 support on both ends.

How many /30 links fit in a /24?

Sixty-four, each using four addresses with two usable.

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