nexonforge — reference tables

reference tables I keep bookmarked

Small collection of lookup tables I need often enough to put on one page. All static HTML — no JavaScript, no tracking, no analytics, no accounts.

IPv4 subnet mask chart #

All 33 prefix lengths, from /0 to /32. Usable hosts excludes network and broadcast addresses, except /31 (RFC 3021 point-to-point) and /32 (single host). Notation per RFC 4632.

CIDR	Netmask	Wildcard	Total	Usable	Notes
/0	0.0.0.0	255.255.255.255	4,294,967,296	—	default route
/1	128.0.0.0	127.255.255.255	2,147,483,648	2,147,483,646
/2	192.0.0.0	63.255.255.255	1,073,741,824	1,073,741,822
/3	224.0.0.0	31.255.255.255	536,870,912	536,870,910
/4	240.0.0.0	15.255.255.255	268,435,456	268,435,454	multicast range starts /4
/5	248.0.0.0	7.255.255.255	134,217,728	134,217,726
/6	252.0.0.0	3.255.255.255	67,108,864	67,108,862
/7	254.0.0.0	1.255.255.255	33,554,432	33,554,430
/8	255.0.0.0	0.255.255.255	16,777,216	16,777,214	class A / 10.0.0.0/8
/9	255.128.0.0	0.127.255.255	8,388,608	8,388,606
/10	255.192.0.0	0.63.255.255	4,194,304	4,194,302	CGNAT 100.64.0.0/10
/11	255.224.0.0	0.31.255.255	2,097,152	2,097,150
/12	255.240.0.0	0.15.255.255	1,048,576	1,048,574	172.16.0.0/12 private
/13	255.248.0.0	0.7.255.255	524,288	524,286
/14	255.252.0.0	0.3.255.255	262,144	262,142
/15	255.254.0.0	0.1.255.255	131,072	131,070
/16	255.255.0.0	0.0.255.255	65,536	65,534	class B / 192.168.0.0/16
/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
/21	255.255.248.0	0.0.7.255	2,048	2,046
/22	255.255.252.0	0.0.3.255	1,024	1,022
/23	255.255.254.0	0.0.1.255	512	510
/24	255.255.255.0	0.0.0.255	256	254	class C
/25	255.255.255.128	0.0.0.127	128	126
/26	255.255.255.192	0.0.0.63	64	62
/27	255.255.255.224	0.0.0.31	32	30
/28	255.255.255.240	0.0.0.15	16	14
/29	255.255.255.248	0.0.0.7	8	6
/30	255.255.255.252	0.0.0.3	4	2	point-to-point
/31	255.255.255.254	0.0.0.1	2	2	RFC 3021 PtP
/32	255.255.255.255	0.0.0.0	1	1	single host

IPv6 common prefixes #

The allocation boundaries worth memorising. See RFC 4291 and the IANA IPv6 address space.

Prefix	Addresses	/64 subnets	Typical use
/32	2⁹⁶	4,294,967,296	Regional ISP allocation
/40	2⁸⁸	16,777,216	Large enterprise
/48	2⁸⁰	65,536	Site / end-user assignment (RIPE recommendation)
/52	2⁷⁶	4,096	Small site
/56	2⁷²	256	Residential customer (common ISP default)
/60	2⁶⁸	16	Minimum home assignment
/64	2⁶⁴	1	Standard subnet — SLAAC requires this
/96	2³²	—	IPv4-embedded / NAT64 (64:ff9b::/96)
/112	2¹⁶	—	Point-to-point convention
/126	4	—	Point-to-point (IPv6 equivalent of /30)
/127	2	—	Point-to-point (RFC 6164)
/128	1	—	Single host

Reserved IP ranges #

The ones that'll bite you if you forget them. Full list: IANA special-purpose registry, RFC 6890.

IPv4 range	Purpose
0.0.0.0/8	"this network" (RFC 1122)
10.0.0.0/8	private (RFC 1918)
100.64.0.0/10	CGNAT (RFC 6598)
127.0.0.0/8	loopback
169.254.0.0/16	link-local / APIPA
172.16.0.0/12	private (RFC 1918)
192.0.0.0/24	IETF protocol assignments
192.0.2.0/24	TEST-NET-1 (docs)
192.168.0.0/16	private (RFC 1918)
198.18.0.0/15	benchmark testing
198.51.100.0/24	TEST-NET-2 (docs)
203.0.113.0/24	TEST-NET-3 (docs)
224.0.0.0/4	multicast
240.0.0.0/4	reserved ("class E")
255.255.255.255/32	limited broadcast

IPv6 range	Purpose
::/128	unspecified
::1/128	loopback
::ffff:0:0/96	IPv4-mapped
64:ff9b::/96	NAT64 well-known
100::/64	discard-only (RFC 6666)
2001:db8::/32	documentation
2001::/23	IETF protocol assignments
2002::/16	6to4
fc00::/7	ULA — unique local
fe80::/10	link-local
ff00::/8	multicast
ff02::1	all-nodes (link)
ff02::2	all-routers (link)
ff02::1:ff00:0/104	solicited-node multicast
2000::/3	global unicast (currently allocated)

DNS record types #

The ones that show up in zones I actually edit. Types are registered at IANA.

A	IPv4 address
AAAA	IPv6 address
CNAME	canonical name alias
MX	mail exchanger (priority + host)
NS	name server delegation
SOA	zone start-of-authority
PTR	reverse DNS pointer
TXT	free-form text (SPF, DMARC, ACME)
SRV	service locator (port + weight)

CAA	cert-issuance authorisation
DNSKEY	DNSSEC signing key
DS	delegation signer
RRSIG	signed record set
NSEC / NSEC3	authenticated denial
TLSA	DANE (cert-binding)
SSHFP	SSH key fingerprint
HTTPS	HTTPS service binding (RFC 9460)
SVCB	generic service binding

HTTP status codes #

The ones I actually see. RFC 9110; the IANA status code registry has the rest.

2xx / 3xx	Meaning
200	OK
201	Created
202	Accepted
204	No Content
206	Partial Content (Range)
301	Moved Permanently
302	Found (see 307/308)
304	Not Modified
307	Temporary Redirect (preserves method)
308	Permanent Redirect (preserves method)

4xx / 5xx	Meaning
400	Bad Request
401	Unauthorized (auth required)
403	Forbidden (auth won't help)
404	Not Found
409	Conflict
422	Unprocessable Entity
429	Too Many Requests
500	Internal Server Error
502	Bad Gateway
503	Service Unavailable
504	Gateway Timeout

Common TCP/UDP ports #

The well-known assignments I reach for without looking up. Authoritative list: IANA service names and port numbers.

20 / 21	FTP data / control
22	SSH
23	Telnet
25	SMTP
53	DNS
67 / 68	DHCP server / client
80	HTTP
110	POP3
123	NTP
143	IMAP
161 / 162	SNMP / traps

389 / 636	LDAP / LDAPS
443	HTTPS / QUIC
465 / 587	SMTPS / submission
514	syslog
993 / 995	IMAPS / POP3S
3306	MySQL / MariaDB
5432	PostgreSQL
6379	Redis
8080	HTTP alt
8443	HTTPS alt
9000	Portainer / PHP-FPM

Unix signals #

Linux x86-64 numbering. Defaults in parentheses. From signal(7).

1	SIGHUP	reload config (term)
2	SIGINT	Ctrl+C (term)
3	SIGQUIT	core (core)
6	SIGABRT	abort (core)
8	SIGFPE	arith error (core)
9	SIGKILL	uncatchable (term)
11	SIGSEGV	segfault (core)
13	SIGPIPE	broken pipe (term)

14	SIGALRM	timer (term)
15	SIGTERM	polite kill (term)
17	SIGCHLD	child state (ign)
18	SIGCONT	resume
19	SIGSTOP	uncatchable stop
20	SIGTSTP	Ctrl+Z (stop)
28	SIGWINCH	window resize (ign)
30	SIGUSR1	user-defined

chmod octal reference #

Each digit = owner / group / other. Combine: read 4, write 2, execute 1. See chmod(1).

Digit	Binary	rwx	Meaning
0	000	---	none
1	001	--x	execute
2	010	-w-	write
3	011	-wx	write + execute
4	100	r--	read
5	101	r-x	read + execute
6	110	rw-	read + write
7	111	rwx	all

Common	Mode	Meaning
644	rw-r--r--	regular file (default)
664	rw-rw-r--	group-writable file
600	rw-------	private (SSH keys, tokens)
640	rw-r-----	config readable by group
755	rwxr-xr-x	script / directory
775	rwxrwxr-x	group-writable dir
700	rwx------	private dir (.ssh)
777	rwxrwxrwx	do not do this
1777	rwxrwxrwt	sticky bit (/tmp)
2755	rwxr-sr-x	setgid directory
4755	rwsr-xr-x	setuid binary

Regex escapes and quantifiers #

PCRE / POSIX ERE — the overlap that works almost everywhere. Reference: pcre2pattern, POSIX regex.

Class	Matches
.	any char (not newline by default)
\d	digit [0-9]
\D	non-digit
\w	word char [A-Za-z0-9_]
\W	non-word
\s	whitespace
\S	non-whitespace
\b	word boundary
\B	non-word-boundary
^	start of line / string
$	end of line / string
\A	start of string (absolute)
\z	end of string (absolute)

Quantifier	Meaning
?	0 or 1
*	0 or more (greedy)
+	1 or more (greedy)
*?	0 or more (lazy)
+?	1 or more (lazy)
{n}	exactly n
{n,}	n or more
{n,m}	n to m
(?:...)	non-capturing group
(?=...)	lookahead
(?!...)	negative lookahead
(?<=...)	lookbehind
(?<!...)	negative lookbehind

SI prefixes #

Base-10, per the BIPM SI brochure.

Symbol	Name	Factor
k	kilo	10³
M	mega	10⁶
G	giga	10⁹
T	tera	10¹²
P	peta	10¹⁵
E	exa	10¹⁸

Symbol	Name	Factor
m	milli	10⁻³
µ	micro	10⁻⁶
n	nano	10⁻⁹
p	pico	10⁻¹²
f	femto	10⁻¹⁵
a	atto	10⁻¹⁸

Byte size units #

Decimal vs. binary. Use the right one. Binary prefixes are IEC 80000-13.

SI (decimal)	Bytes
kB	1,000
MB	1,000,000
GB	1,000,000,000
TB	10¹²
PB	10¹⁵

IEC (binary)	Bytes
KiB	1,024
MiB	1,048,576
GiB	1,073,741,824
TiB	2⁴⁰
PiB	2⁵⁰

ANSI color escape codes #

Prefix with \e[ and suffix with m. Reset is 0. ECMA-48 / console_codes(4).

Code	Foreground
30	black
31	red
32	green
33	yellow
34	blue
35	magenta
36	cyan
37	white
90-97	bright variants

Code	Attribute
0	reset all
1	bold
2	dim
3	italic
4	underline
7	reverse
9	strikethrough
40-47	background (same colors)

Common timezone offsets #

Standard time. DST shifts by +1h where applicable. Canonical data: IANA tz database.

UTC+0	UTC / GMT / WET / Reykjavik
UTC+1	CET — Berlin, Paris, Madrid
UTC+2	EET — Athens, Helsinki, Kyiv
UTC+3	Moscow, Istanbul, Riyadh
UTC+4	Dubai, Baku
UTC+5:30	IST — India
UTC+7	Bangkok, Jakarta
UTC+8	Beijing, Singapore, Perth

UTC+9	JST — Tokyo, Seoul
UTC+10	AEST — Sydney
UTC+12	NZST — Auckland
UTC−3	São Paulo, Buenos Aires
UTC−5	EST — New York, Toronto
UTC−6	CST — Chicago, Mexico City
UTC−7	MST — Denver
UTC−8	PST — LA, Vancouver

ASCII table #

0–127. Control characters greyed. Everything above 127 is not ASCII, whatever the codepage says. RFC 20.

Dec	Hex	Char
0	0x00	NUL
1	0x01	SOH
2	0x02	STX
3	0x03	ETX
4	0x04	EOT
5	0x05	ENQ
6	0x06	ACK
7	0x07	BEL
8	0x08	BS
9	0x09	HT
10	0x0A	LF
11	0x0B	VT
12	0x0C	FF
13	0x0D	CR
14	0x0E	SO
15	0x0F	SI
16	0x10	DLE
17	0x11	DC1
18	0x12	DC2
19	0x13	DC3
20	0x14	DC4
21	0x15	NAK
22	0x16	SYN
23	0x17	ETB
24	0x18	CAN
25	0x19	EM
26	0x1A	SUB
27	0x1B	ESC
28	0x1C	FS
29	0x1D	GS
30	0x1E	RS
31	0x1F	US

Dec	Hex	Char
32	0x20	SP
33	0x21	!
34	0x22	"
35	0x23	#
36	0x24	$
37	0x25	%
38	0x26	&
39	0x27	'
40	0x28	(
41	0x29	)
42	0x2A	*
43	0x2B	+
44	0x2C	,
45	0x2D	-
46	0x2E	.
47	0x2F	/
48	0x30	0
49	0x31	1
50	0x32	2
51	0x33	3
52	0x34	4
53	0x35	5
54	0x36	6
55	0x37	7
56	0x38	8
57	0x39	9
58	0x3A	:
59	0x3B	;
60	0x3C	<
61	0x3D	=
62	0x3E	>
63	0x3F	?

Dec	Hex	Char
64	0x40	@
65	0x41	A
66	0x42	B
67	0x43	C
68	0x44	D
69	0x45	E
70	0x46	F
71	0x47	G
72	0x48	H
73	0x49	I
74	0x4A	J
75	0x4B	K
76	0x4C	L
77	0x4D	M
78	0x4E	N
79	0x4F	O
80	0x50	P
81	0x51	Q
82	0x52	R
83	0x53	S
84	0x54	T
85	0x55	U
86	0x56	V
87	0x57	W
88	0x58	X
89	0x59	Y
90	0x5A	Z
91	0x5B	[
92	0x5C	\
93	0x5D	]
94	0x5E	^
95	0x5F	_

Dec	Hex	Char
96	0x60	`
97	0x61	a
98	0x62	b
99	0x63	c
100	0x64	d
101	0x65	e
102	0x66	f
103	0x67	g
104	0x68	h
105	0x69	i
106	0x6A	j
107	0x6B	k
108	0x6C	l
109	0x6D	m
110	0x6E	n
111	0x6F	o
112	0x70	p
113	0x71	q
114	0x72	r
115	0x73	s
116	0x74	t
117	0x75	u
118	0x76	v
119	0x77	w
120	0x78	x
121	0x79	y
122	0x7A	z
123	0x7B	{
124	0x7C	\|
125	0x7D	}
126	0x7E	~
127	0x7F	DEL

Common MIME types #

What goes in Content-Type. Full registry at IANA.

Type	Extension / use
text/html	.html
text/css	.css
text/plain	.txt
text/csv	.csv
text/javascript	.js, .mjs
application/json	.json
application/xml	.xml
application/pdf	.pdf
application/zip	.zip
application/gzip	.gz
application/octet-stream	anything binary
application/x-www-form-urlencoded	form posts
multipart/form-data	file uploads
application/wasm	.wasm

Type	Extension / use
application/manifest+json	.webmanifest
image/png	.png
image/jpeg	.jpg, .jpeg
image/gif	.gif
image/webp	.webp
image/avif	.avif
image/svg+xml	.svg
image/x-icon	.ico
font/woff2	.woff2
font/ttf	.ttf
audio/mpeg	.mp3
audio/ogg	.ogg, .oga
video/mp4	.mp4
video/webm	.webm