Category: General Info

Adding a DKIM record to your DNS

Adding a DKIM record to your DNS is quite simple. Add two txt records like

_domainkey.domain.com          IN TXT o=!;r=postmaster@domain.com
selector._domainkey.domain.com IN TXT v=DKIM1;k=rsa;p=<public key>

Which means:

  • o=~ the server signs some mail
  • o=- all mail is signed, but unsigned mail should be accepted
  • o=! all mail is signed, do not accept unsigned mail
  • t=y I’m still testing
  • v=DKIM1 we use DKIM version 1
  • k=rsa it is a RSA key
  • r=<x@xx> report problems to this email address
  • p=<public key> this is my public key

Subnet Masks

subnetwork, or subnet, is a logically visible, distinctly addressed part of a single Internet Protocol network. The process of subnetting is the division of a computer network into groups of computers that have a common, designated IP address routing prefix.

/binaryhexdecimal
/110000000.00000000.00000000.000000000x80000000128.0.0.0
/211000000.00000000.00000000.000000000xc0000000192.0.0.0
/311100000.00000000.00000000.000000000xe0000000224.0.0.0
/411110000.00000000.00000000.000000000xf0000000240.0.0.0
/511111000.00000000.00000000.000000000xf8000000248.0.0.0
/611111100.00000000.00000000.000000000xfc000000252.0.0.0
/711111110.00000000.00000000.000000000xfe000000254.0.0.0
/811111111.00000000.00000000.000000000xff000000255.0.0.0
/911111111.10000000.00000000.000000000xff800000255.128.0.0
/1011111111.11000000.00000000.000000000xffc00000255.192.0.0
/1111111111.11100000.00000000.000000000xffe00000255.224.0.0
/1211111111.11110000.00000000.000000000xfff00000255.240.0.0
/1311111111.11111000.00000000.000000000xfff80000255.248.0.0
/1411111111.11111100.00000000.000000000xfffc0000255.252.0.0
/1511111111.11111110.00000000.000000000xfffe0000255.254.0.0
/1611111111.11111111.00000000.000000000xffff0000255.255.0.0
/1711111111.11111111.10000000.000000000xffff8000255.255.128.0
/1811111111.11111111.11000000.000000000xffffc000255.255.192.0
/1911111111.11111111.11100000.000000000xffffe000255.255.224.0
/2011111111.11111111.11110000.000000000xfffff000255.255.240.0
/2111111111.11111111.11111000.000000000xfffff800255.255.248.0
/2211111111.11111111.11111100.000000000xfffffc00255.255.252.0
/2311111111.11111111.11111110.000000000xfffffe00255.255.254.0
/2411111111.11111111.11111111.000000000xffffff00255.255.255.0
/2511111111.11111111.11111111.100000000xffffff80255.255.255.128
/2611111111.11111111.11111111.110000000xffffffc0255.255.255.192
/2711111111.11111111.11111111.111000000xffffffe0255.255.255.224
/2811111111.11111111.11111111.111100000xfffffff0255.255.255.240
/2911111111.11111111.11111111.111110000xfffffff8255.255.255.248
/3011111111.11111111.11111111.111111000xfffffffc255.255.255.252
/3111111111.11111111.11111111.111111100xfffffffe255.255.255.254
/3211111111.11111111.11111111.111111110xffffffff255.255.255.255

SI prefixes

An SI prefix is a name that precedes a basic unit of measure to indicate a decimal multiple or fraction of the unit. Each prefix has a unique symbol that is prepended to the unit symbol.

NameZeichenPotenzFaktor
YottaY10241.000.000.000.000.000.000.000.000
ZettaZ10211.000.000.000.000.000.000.000
ExaE10181.000.000.000.000.000.000
PetaP10151.000.000.000.000.000
TeraT10121.000.000.000.000
GigaG1091.000.000.000
MegaM1061.000.000
Kilok1031.000
Hektoh102100
Dekada10110
Dezid10-10,1
Zentic10-20,01
Millim10-30,001
Mikroµ10-60,000.001
Nanon10-90,000.000.001
Picop10-120,000.000.000.001
Femtof10-150,000.000.000.000.001
Attoa10-180,000.000.000.000.000.001
Zeptoz10-210,000.000.000.000.000.000.001
Yoctoy10-240,000.000.000.000.000.000.000.001