use strict;
use warnings;

my $lastIP;

while (<DATA>) {
  print if /network name|interface name|VRID|state|primary address/i;
  print "$lastIP\n\n" if /Monitored circuits:/ and defined $lastIP;
  $lastIP = $1 if /((\d{1,3}\.){3}\d{1,3})/;
}

##</code><code>##

__DATA__
Network name A
Interface WEB_A
    ggggggggg
        VRID 145
        State:        Master    
                   XXXXXXXXXXXX
    Effective  Priority:    200
        07:09:56:04:0t:ef
        Primary address:    194.551.205.250
        Number addresses:    1
        135.51.045.242
Monitored circuits:
            vbgghdfgdfg
Interface WEB_B
    ggggggggg
    Agggggg
    VRID 145
        State:        backup    
                   XXXXXXXXXXXX
    Effective  Priority:    200
        07:09:56:04:0t:ef
        Primary address:    19.51.205.20
        Next advertisement:    0
        Number addresses:    1
            135.51.05.22
        Monitored circuits:
            vbgghdfgdfg

##</code><code>##

Network name A
        VRID 145
        State:        Master    
        Primary address:    194.551.205.250
135.51.045.242

    VRID 145
        State:        backup    
        Primary address:    19.51.205.20
135.51.05.22