The table every network person looks up weekly, as two pages to print: prefixes with masks, wildcard masks and host counts, the special ranges, the ports worth knowing by heart, and a table for your own VLANs that you fill in before printing.
Two pages, A4 or Letter, portrait. Switch off headers and footers in the print dialog.
IPv4 prefixes
Prefix
Subnet mask
Wildcard
Addresses
Usable hosts
Think of it as
/8
255.0.0.0
0.255.255.255
16,777,216
16,777,214
class A size
/12
255.240.0.0
0.15.255.255
1,048,576
1,048,574
/16
255.255.0.0
0.0.255.255
65,536
65,534
class B size, 256 times a /24
/17
255.255.128.0
0.0.127.255
32,768
32,766
/18
255.255.192.0
0.0.63.255
16,384
16,382
/19
255.255.224.0
0.0.31.255
8,192
8,190
/20
255.255.240.0
0.0.15.255
4,096
4,094
16 times a /24
/21
255.255.248.0
0.0.7.255
2,048
2,046
8 times a /24
/22
255.255.252.0
0.0.3.255
1,024
1,022
4 times a /24
/23
255.255.254.0
0.0.1.255
512
510
2 times a /24
/24
255.255.255.0
0.0.0.255
256
254
the everyday network
/25
255.255.255.128
0.0.0.127
128
126
half a /24: .0 and .128
/26
255.255.255.192
0.0.0.63
64
62
a quarter: .0 .64 .128 .192
/27
255.255.255.224
0.0.0.31
32
30
blocks of 32
/28
255.255.255.240
0.0.0.15
16
14
blocks of 16
/29
255.255.255.248
0.0.0.7
8
6
blocks of 8
/30
255.255.255.252
0.0.0.3
4
2
blocks of 4: router links
/31
255.255.255.254
0.0.0.1
2
2 (point to point)
router links, no waste
/32
255.255.255.255
0.0.0.0
1
1 (a single host)
one address: host routes
In your head: block size = 256 minus the interesting mask byte. /26 has mask .192, so blocks of 64: networks start at .0, .64, .128, .192. The first address of a block is the network, the last is the broadcast, everything between is for hosts.
ranges with a meaning
10.0.0.0/8
private
172.16.0.0/12
private: 172.16 to 172.31
192.168.0.0/16
private
100.64.0.0/10
carrier NAT: your provider's, not yours
169.254.0.0/16
self-assigned: DHCP did not answer
127.0.0.0/8
this machine itself
224.0.0.0/4
multicast
192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24
for documentation only
fe80::/10
IPv6 link-local
fc00::/7
IPv6 private (ULA)
2001:db8::/32
IPv6 for documentation
ports worth knowing
22
SSH, SFTP
25, 587, 465
SMTP: server to server, submission, submission over TLS
53
DNS (UDP and TCP)
67, 68
DHCP (UDP)
80, 443
HTTP, HTTPS
88
Kerberos
123
NTP (UDP)
135, 445
RPC, SMB file sharing
143, 993
IMAP, IMAP over TLS
161, 162
SNMP, SNMP traps (UDP)
389, 636
LDAP, LDAP over TLS
514
syslog (UDP)
1433, 3306, 5432
SQL Server, MySQL, PostgreSQL
3389
Remote Desktop
5060, 5061
SIP, SIP over TLS
5985, 5986
WinRM, PowerShell remoting
9100
printing (raw)
VLANs in five lines
A VLAN is a separate switch inside the switch. Devices in different VLANs reach each other only through a router or firewall.
An access port belongs to one VLAN and sends plain frames: for PCs, printers, servers.
A trunk port carries several VLANs, each frame tagged with its VLAN number (802.1Q): between switches, to access points, to hypervisors.
The native VLAN of a trunk travels untagged. It must be the same on both ends, and should not be VLAN 1.
One VLAN, one subnet, one gateway. Write all three in the table below.
our VLANs
VLAN
Name
Subnet
Gateway
DHCP range
For
Type into the cells. Nothing is stored: print it when it is right.