Network Management Hint: Sort by IP Address

Network Management Hint: Sort by IP Address

How do you sort a host table by IP Address on a UNIX network management platform?

This has been a basic requirement, since the dawn of The Internet.

Let's look at an example /etc/hosts extract:

sun9999/user$ cat /etc/hosts

#
127.0.0.1       localhost
::1             localhost

201.14.24.17    BT-Site-1       # LasPalmas
203.16.54.112   QB-Site-1       # NorthSydney
201.14.24.21    DL-Site-1       # LasPalmas
202.135.192.97  QB-Site-1       # NorthSydney
203.16.54.18    PR-Site-1       # NorthSydney
201.14.24.28    DL-Site-2       # LasPalmas
203.16.54.22    KP-Site-1       # NorthSydney

Each octet in an IPv4 address is separated by a period "." and a simple POSIX sort will use the period as the field separator and then request a numeric sort on the first, second, third, and fourth octets.

sun9999/user$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts

::1 localhost
#
127.0.0.1       localhost
201.14.24.17    BT-Site-1     # LasPalmas
201.14.24.21    DL-Site-1     # LasPalmas
201.14.24.28    DL-Site-2     # LasPalmas
202.135.192.97  QB-Site-1     # NorthSydney
203.16.54.18    PR-Site-1     # NorthSydney
203.16.54.22    KP-Site-1     # NorthSydney
203.16.54.112   QB-Site-1     # NorthSydney

What it you want to eliminate colon ":" separated IPv6 addresses, empty lines, and lines with comments? Just perform a little POSIX awk'ing after the sort.

sun9999/user$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts | awk '$1!~/:/ && !/^$/ && !/^#/'

127.0.0.1       localhost
201.14.24.17    BT-Site-1       # LasPalmas
201.14.24.21    DL-Site-1       # LasPalmas
201.14.24.28    DL-Site-2       # LasPalmas
202.135.192.97  QB-Site-1       # NorthSydney
203.16.54.18    PR-Site-1       # NorthSydney
203.16.54.22    KP-Site-1       # NorthSydney
203.16.54.112   QB-Site-1       # NorthSydney

Want to eliminate all localhost entries? Add a localhost elimination pattern:

sun9999/user$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts | awk '$1!~/:/ && !/^$/ && !/^#/ && !/localhost/'

201.14.24.17    BT-Site-1       # LasPalmas
201.14.24.21    DL-Site-1       # LasPalmas
201.14.24.28    DL-Site-2       # LasPalmas
202.135.192.97  QB-Site-1       # NorthSydney
203.16.54.18    PR-Site-1       # NorthSydney
203.16.54.22    KP-Site-1       # NorthSydney
203.16.54.112   QB-Site-1       # NorthSydney

Need to print only the host name, sorted by IP Address, for entries managed by NorthSydney NOC?

sun9999/user$ sort -t . -k 1,1n -k 2,2n -k 3,3n -k 4,4n /etc/hosts | 
awk '$1!~/:/ && !/^$/ && !/^#/ && !/localhost/ && /NorthSydney/ { 
print $2 }'
QB-Site-1
PR-Site-1
KP-Site-1
QB-Site-1

If you are not using POSIX commands to do standard network management work, you don't know what you are missing!