CIDR Cheat Sheet – IP Subnet & Netmask info

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This cidr cheat sheet provides a quick lookup table for common subnet and netmask calculations/translations. Must have for sysadmins and network engineers. Print out a copy and pin it up in your office.

CIDR Cheat Sheet

CIDR Cheat Sheet
 
Netmask              Netmask (binary)                 CIDR     Notes    
_____________________________________________________________________________
255.255.255.255  11111111.11111111.11111111.11111111  /32  Host (single addr)
255.255.255.254  11111111.11111111.11111111.11111110  /31  Unuseable
255.255.255.252  11111111.11111111.11111111.11111100  /30    2  useable
255.255.255.248  11111111.11111111.11111111.11111000  /29    6  useable
255.255.255.240  11111111.11111111.11111111.11110000  /28   14  useable
255.255.255.224  11111111.11111111.11111111.11100000  /27   30  useable
255.255.255.192  11111111.11111111.11111111.11000000  /26   62  useable
255.255.255.128  11111111.11111111.11111111.10000000  /25  126  useable
255.255.255.0    11111111.11111111.11111111.00000000  /24 "Class C" 254 useable
 
255.255.254.0    11111111.11111111.11111110.00000000  /23    2  Class C's
255.255.252.0    11111111.11111111.11111100.00000000  /22    4  Class C's
255.255.248.0    11111111.11111111.11111000.00000000  /21    8  Class C's
255.255.240.0    11111111.11111111.11110000.00000000  /20   16  Class C's
255.255.224.0    11111111.11111111.11100000.00000000  /19   32  Class C's
255.255.192.0    11111111.11111111.11000000.00000000  /18   64  Class C's
255.255.128.0    11111111.11111111.10000000.00000000  /17  128  Class C's
255.255.0.0      11111111.11111111.00000000.00000000  /16  "Class B"
 
255.254.0.0      11111111.11111110.00000000.00000000  /15    2  Class B's
255.252.0.0      11111111.11111100.00000000.00000000  /14    4  Class B's
255.248.0.0      11111111.11111000.00000000.00000000  /13    8  Class B's
255.240.0.0      11111111.11110000.00000000.00000000  /12   16  Class B's
255.224.0.0      11111111.11100000.00000000.00000000  /11   32  Class B's
255.192.0.0      11111111.11000000.00000000.00000000  /10   64  Class B's
255.128.0.0      11111111.10000000.00000000.00000000  /9   128  Class B's
255.0.0.0        11111111.00000000.00000000.00000000  /8   "Class A"
 
254.0.0.0        11111110.00000000.00000000.00000000  /7
252.0.0.0        11111100.00000000.00000000.00000000  /6
248.0.0.0        11111000.00000000.00000000.00000000  /5
240.0.0.0        11110000.00000000.00000000.00000000  /4
224.0.0.0        11100000.00000000.00000000.00000000  /3
192.0.0.0        11000000.00000000.00000000.00000000  /2
128.0.0.0        10000000.00000000.00000000.00000000  /1
0.0.0.0          00000000.00000000.00000000.00000000  /0   IP space
 
                                   Net     Host    Total
Net      Addr                      Addr    Addr    Number
Class   Range      NetMask         Bits    Bits   of hosts
----------------------------------------------------------
A        0-127    255.0.0.0         8      24     16777216   (i.e. 114.0.0.0)
B      128-191    255.255.0.0      16      16        65536   (i.e. 150.0.0.0)
C      192-254    255.255.255.0    24       8          256   (i.e. 199.0.0.0)
D      224-239    (multicast)
E      240-255    (reserved)
F      208-215    255.255.255.240  28       4           16
G      216/8      ARIN - North America
G      217/8      RIPE NCC - Europe
G      218-219/8  APNIC
H      220-221    255.255.255.248  29       3            8   (reserved)
K      222-223    255.255.255.254  31       1            2   (reserved)
(ref: RFC1375 & http://www.iana.org/assignments/ipv4-address-space )
(               http://www.iana.org/numbers.htm                    )
----------------------------------------------------------
 
The current list of special use prefixes:
	0.0.0.0/8	
	127.0.0.0/8
	192.0.2.0/24
	10.0.0.0/8
	172.16.0.0/12
	192.168.0.0/16
	169.254.0.0/16
	all D/E space
(ref: RFC1918 http://www.rfc-editor.org/rfc/rfc1918.txt   )
(       or     ftp://ftp.isi.edu/in-notes/rfc1918.txt     )
(rfc search:   http://www.rfc-editor.org/rfcsearch.html   )
(              http://www.ietf.org/ietf/1id-abstracts.txt )
(              http://www.ietf.org/shadow.html            )
 
 
Martians: (updates at: www.iana.org/assignments/ipv4-address-space )
 no ip source-route
 access-list 100 deny   ip host 0.0.0.0 any
  deny ip 0.0.0.0         0.255.255.255  any log  ! antispoof
  deny ip 0.0.0.0 0.255.255.255  0.0.0.0 255.255.255.255 ! antispoof
  deny ip any             255.255.255.128 0.0.0.127 ! antispoof
  deny ip host            0.0.0.0        any log  ! antispoof
  deny ip host            [router intf]  [router intf] ! antispoof
  deny ip xxx.xxx.xxx.0   0.0.0.255      any log  ! lan area
  deny ip 0/8             0.255.255.255  any log  ! IANA - Reserved
  deny ip 1/8             0.255.255.255  any log  ! IANA - Reserved
  deny ip 2/8             0.255.255.255  any log  ! IANA - Reserved
  deny ip 5/8             0.255.255.255  any log  ! IANA - Reserved
  deny ip 7/8             0.255.255.255  any log  ! IANA - Reserved
  deny ip 10.0.0.0        0.255.255.255  any log  ! IANA - Private Use
  deny ip 23/8            0.255.255.255  any log  ! IANA - Reserved
  deny ip 27/8            0.255.255.255  any log  ! IANA - Reserved
  deny ip 31/8            0.255.255.255  any log  ! IANA - Reserved
  deny ip 36-37/8         0.255.255.255  any log  ! IANA - Reserved
  deny ip 39/8            0.255.255.255  any log  ! IANA - Reserved
  deny ip 41-42/8         0.255.255.255  any log  ! IANA - Reserved
  deny ip 50/8            0.255.255.255  any log  ! IANA - Reserved
  deny ip 58-60/8         0.255.255.255  any log  ! IANA - Reserved
  deny ip 69-79/8         0.255.255.255  any log  ! IANA - Reserved
  deny ip 82-95/8         0.255.255.255  any log  ! IANA - Reserved
  deny ip 96-126/8        0.255.255.255  any log  ! IANA - Reserved
  deny ip 127/8           0.255.255.255  any log  ! IANA - Reserved
  deny ip 169.254.0.0     0.0.255.255    any log  ! link-local network
  deny ip 172.16.0.0      0.15.255.255   any log  ! reserved
  deny ip 192.168.0.0     0.0.255.255    any log  ! reserved
  deny ip 192.0.2.0       0.0.0.255      any log  ! test network
  deny ip 197/8           0.255.255.255  any log  ! IANA - Reserved
  deny ip 220/8           0.255.255.255  any log  ! IANA - Reserved
  deny ip 222-223/8       0.255.255.255  any log  ! IANA - Reserved
  deny ip 224.0.0.0       31.255.255.255 any log  ! multicast
  deny ip 224.0.0.0       15.255.255.255 any log  ! unless MBGP-learned routes
  deny ip 224-239/8       0.255.255.255  any log  ! IANA - Multicast
  deny ip 240-255/8       0.255.255.255  any log  ! IANA - Reserved
 
filtered source addresses
  0/8                 ! broadcast
  10/8                ! RFC 1918 private
  127/8               ! loopback
  169.254.0/16        ! link local
  172.16.0.0/12       ! RFC 1918 private
  192.0.2.0/24        ! TEST-NET
  192.168.0/16        ! RFC 1918 private
  224.0.0.0/4         ! class D multicast
  240.0.0.0/5         ! class E reserved
  248.0.0.0/5         ! reserved
  255.255.255.255/32  ! broadcast
 
ARIN administrated blocks: (http://www.arin.net/regserv/IPStats.html)
   24.0.0.0/8 (portions of)
   63.0.0.0/8
   64.0.0.0/8
   65.0.0.0/8
   66.0.0.0/8
  196.0.0.0/8
  198.0.0.0/8
  199.0.0.0/8
  200.0.0.0/8
  204.0.0.0/8
  205.0.0.0/8
  206.0.0.0/8
  207.0.0.0/8
  208.0.0.0/8
  209.0.0.0/8
  216.0.0.0/8

A coworker linked me to this great cidr cheat sheet. I’m mirroring a copy of it here for future reference and availability. http://www.oav.net/mirrors/cidr.html

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