IPV6 Reference

2001:0db8:0123:4567:89ab:cdef:1234:5678
|||| |||| |||| |||| |||| |||| |||| ||||
|||| |||| |||| |||| |||| |||| |||| |||128     Single end-points and loopback
|||| |||| |||| |||| |||| |||| |||| |||127   Point-to-point links (inter-router)
|||| |||| |||| |||| |||| |||| |||| ||124
|||| |||| |||| |||| |||| |||| |||| |120
|||| |||| |||| |||| |||| |||| |||| 116
|||| |||| |||| |||| |||| |||| |||112
|||| |||| |||| |||| |||| |||| ||108
|||| |||| |||| |||| |||| |||| |104
|||| |||| |||| |||| |||| |||| 100
|||| |||| |||| |||| |||| |||96
|||| |||| |||| |||| |||| ||92
|||| |||| |||| |||| |||| |88
|||| |||| |||| |||| |||| 84
|||| |||| |||| |||| |||80
|||| |||| |||| |||| ||76
|||| |||| |||| |||| |72
|||| |||| |||| |||| 68
|||| |||| |||| |||64   Single End-user LAN (default prefix size for SLAAC)
|||| |||| |||| ||60   Some (very limited) 6rd deployments (/60 = 16 /64)
|||| |||| |||| |56   Minimal end sites assignment[3] (e.g. Home network) (/56 = 256 /64)
|||| |||| |||| 52   (/52 = 4096 /64)
|||| |||| |||48   Typical assignment for larger sites (/48 = 65536 /64)
|||| |||| ||44
|||| |||| |40
|||| |||| 36   possible future Local Internet registry extra-small allocations
|||| |||32   Local Internet registry minimum allocations
|||| ||28   Local Internet registry medium allocations
|||| |24   Local Internet registry large allocations
|||| 20   Local Internet registry extra large allocations
|||16
||12   Regional Internet Registry allocations from IANA[4]
|8
4

IPV6 explained by Kieth Barker https://www.youtube.com/watch?v=rljkNMySmuM
Google’s IPV6 usage chart https://www.google.com/intl/en/ipv6/statistics.html

IPV4 Subnet Reference

 

CIDR Length Mask # Networks       # Hosts
  /1 128.0.0.0 128 A       2,147,483,392
  /2 192.0.0.0 64 A       1,073,741,696
  /3 224.0.0.0 32 A         536,870,848
  /4 240.0.0.0 16 A   268,435,424
  /5 248.0.0.0 8 A   134,217,712
  /6 252.0.0.0 4 A 67,108,856
  /7 254.0.0.0 2 A 33,554,428
  /8 255.0.0.0 1 A   16,777,214
  /9 255.128.0.0 128 B 8,388,352
  /10 255.192.0.0 64 B 4,194,176
  /11 255.224.0.0 32 B 2,097,088
  /12 255.240.0.0 16 B 1,048,544
  /13 255.248.0.0 8 B 524,272
  /14 255.252.0.0 4 B 262,136
  /15 255.254.0.0 2 B 131,068
  /16 255.255.0.0 1 B 65,024
  /17 255.255.128.0 128 C 32,512
  /18 255.255.192.0 64 C   16,256
  /19 255.255.224.0 32 C   8,128
  /20 255.255.240.0 16 C   4,064
  /21 255.255.248.0 8 C   2,032
  /22 255.255.252.0 4 C   1,016
  /23 255.255.254.0 2 C   508
  /24 255.255.255.0 1 C   254
  /25 255.255.255.128   2 subnets 124
  /26 255.255.255.192   4 subnets 62
  /27 255.255.255.224   8 subnets 30
  /28 255.255.255.240   16 subnets 14
  /29 255.255.255.248 32 subnets 6
  /30 255.255.255.252 64 subnets 2
  /31   255.255.255.254   none                    none
 /32 255.255.255.255         1/256 C                            1

NTP on CentOS

You can easily install NTP (Network Time Protocol, a means of transmitting time signals over a computer network) using the yum command under Red Hat or CentOS/Fedora Linux server or workstation based systems. You need to install the following packages:

 

  1. ntp : ntpd server which continuously adjusts system time and utilities used to query and configure the ntpd daemon.
  2. ntpdate : Utility to set the date and time via NTP.
  3. ntp-doc : NTP documentation

Procedure: Setup NTPD on CentOS Linux

Open the terminal or login over the ssh session. You must login as as the root user. Type the following yum command to install ntp
# yum install ntp ntpdate ntp-doc

Turn on service, enter:
# chkconfig ntpd on

Synchronize the system clock with 0.pool.ntp.org server (use this command only once or as required):
# ntpdate pool.ntp.org

Start the NTP server. The following will continuously adjusts system time from upstream NTP server. No need to run ntpdate:
# /etc/init.d/ntpd start

Configure ntpd (optional)

Edit /etc/ntp.conf, enter:
# vi /etc/ntp.conf
Set public servers from the pool.ntp.org project:

server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org