172.18.0.0/16

Private (RFC 1918) RFC 1918

Docker Compose typically assigns 172.18.0.0/16 to the first user-defined bridge network it creates. When running `docker-compose up`, each project gets its own subnet in the 172.x.0.0/16 range, starting from 172.17 and incrementing.

Network Address

172.18.0.0

Broadcast Address

172.18.255.255

Subnet Mask

255.255.0.0

Usable Hosts

65,534

First Usable IP

172.18.0.1

Last Usable IP

172.18.255.254

Total IPs

65,536

Prefix Length

/16

Network address — the base address of the block (172.18.0.0). All devices in this subnet share this prefix. Cannot be assigned to a host.

Broadcast address — packets sent to 172.18.255.255 are delivered to every device in the subnet. Also reserved — not assignable.

Usable hosts — the 65,534 addresses between those two that you can assign to servers, VMs, or interfaces.

Subnet mask — 255.255.0.0 is the dotted-decimal equivalent of /16. Older tools and Cisco configs use this format instead of CIDR slash notation.

Full Details

CIDR Notation	172.18.0.0/16
Network Address	172.18.0.0
Broadcast Address	172.18.255.255
Subnet Mask	255.255.0.0
Wildcard Mask	0.0.255.255
Prefix Length	/16
IP Address Class	Class B
Total IP Addresses	65,536
Usable Host Addresses	65,534
First Usable IP	172.18.0.1
Last Usable IP	172.18.255.254
Network (Hex)	0xAC120000
Broadcast (Hex)	0xAC12FFFF
Governing RFC	RFC 1918
Address Type	Private (RFC 1918)

Binary Representation

Network Address

10101100.00010010 10101100.00010010.00000000.00000000

Subnet Mask

11111111.11111111.00000000.00000000

The first 16 bits (1s in the mask) identify the network. The remaining 16 bits identify hosts within the network.

Split into Equal Subnets

Split 172.18.0.0/16 into 2 equal /17 subnets (32,766 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	172.18.0.0/17	172.18.0.0	172.18.0.1	172.18.127.254	172.18.127.255	32,766
2	172.18.128.0/17	172.18.128.0	172.18.128.1	172.18.255.254	172.18.255.255	32,766

Split 172.18.0.0/16 into 4 equal /18 subnets (16,382 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	172.18.0.0/18	172.18.0.0	172.18.0.1	172.18.63.254	172.18.63.255	16,382
2	172.18.64.0/18	172.18.64.0	172.18.64.1	172.18.127.254	172.18.127.255	16,382
3	172.18.128.0/18	172.18.128.0	172.18.128.1	172.18.191.254	172.18.191.255	16,382
4	172.18.192.0/18	172.18.192.0	172.18.192.1	172.18.255.254	172.18.255.255	16,382

Split 172.18.0.0/16 into 8 equal /19 subnets (8,190 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	172.18.0.0/19	172.18.0.0	172.18.0.1	172.18.31.254	172.18.31.255	8,190
2	172.18.32.0/19	172.18.32.0	172.18.32.1	172.18.63.254	172.18.63.255	8,190
3	172.18.64.0/19	172.18.64.0	172.18.64.1	172.18.95.254	172.18.95.255	8,190
4	172.18.96.0/19	172.18.96.0	172.18.96.1	172.18.127.254	172.18.127.255	8,190
5	172.18.128.0/19	172.18.128.0	172.18.128.1	172.18.159.254	172.18.159.255	8,190
6	172.18.160.0/19	172.18.160.0	172.18.160.1	172.18.191.254	172.18.191.255	8,190
7	172.18.192.0/19	172.18.192.0	172.18.192.1	172.18.223.254	172.18.223.255	8,190
8	172.18.224.0/19	172.18.224.0	172.18.224.1	172.18.255.254	172.18.255.255	8,190

Split 172.18.0.0/16 into 16 equal /20 subnets (4,094 usable hosts each).

#	CIDR	Network	First Usable	Last Usable	Broadcast	Hosts
1	172.18.0.0/20	172.18.0.0	172.18.0.1	172.18.15.254	172.18.15.255	4,094
2	172.18.16.0/20	172.18.16.0	172.18.16.1	172.18.31.254	172.18.31.255	4,094
3	172.18.32.0/20	172.18.32.0	172.18.32.1	172.18.47.254	172.18.47.255	4,094
4	172.18.48.0/20	172.18.48.0	172.18.48.1	172.18.63.254	172.18.63.255	4,094
5	172.18.64.0/20	172.18.64.0	172.18.64.1	172.18.79.254	172.18.79.255	4,094
6	172.18.80.0/20	172.18.80.0	172.18.80.1	172.18.95.254	172.18.95.255	4,094
7	172.18.96.0/20	172.18.96.0	172.18.96.1	172.18.111.254	172.18.111.255	4,094
8	172.18.112.0/20	172.18.112.0	172.18.112.1	172.18.127.254	172.18.127.255	4,094
9	172.18.128.0/20	172.18.128.0	172.18.128.1	172.18.143.254	172.18.143.255	4,094
10	172.18.144.0/20	172.18.144.0	172.18.144.1	172.18.159.254	172.18.159.255	4,094
11	172.18.160.0/20	172.18.160.0	172.18.160.1	172.18.175.254	172.18.175.255	4,094
12	172.18.176.0/20	172.18.176.0	172.18.176.1	172.18.191.254	172.18.191.255	4,094
13	172.18.192.0/20	172.18.192.0	172.18.192.1	172.18.207.254	172.18.207.255	4,094
14	172.18.208.0/20	172.18.208.0	172.18.208.1	172.18.223.254	172.18.223.255	4,094
15	172.18.224.0/20	172.18.224.0	172.18.224.1	172.18.239.254	172.18.239.255	4,094
16	172.18.240.0/20	172.18.240.0	172.18.240.1	172.18.255.254	172.18.255.255	4,094