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IPv6 shortening and compressing address rules

Posted on by Biafra

An IPv6 address can be very long as it is a 128 bits one. Asking someone verbally to check the connectivity to a given address can be tricky :-)

There are however some rules to shorten it and it’s a way to remove zeros.

Rule 1: Suppress leading zeros

Remove all leading zeros, the left side zeros, in every 16 bits field.

For example:

2001:0db8:0000:0000:0000:0000:000:0001

will be simplified to

2001:db8:0:0:0:0:0:1

Of course 0000 becomes 0.

Rules 2: The larger sequence of :0:0: can be reduced to ::

You can compact a sequence of zeros to the symbol ::.

Applying the rule to 2001:db8:0:0:0:0:0:1 would get us 2001:db8::1.

  • You can’t compact just one :0: – only a sequence.
  • If there is more than one sequence of :0: you can only compact the large one. If they have the same length compact the first one.

2001:db8::1:1:1:1:1 is not correct. It must be 2001:db8:0:1:1:1:1:1.

2001:0:0:1:0:0:0:1 will become 2001:0:0:1::1.

2001:db8:0:0:1:0:0:1 will become 2001:db8::1:0:0:1.

That’s it.

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How to check an SSL certificate expiration date from the command line

Posted on by Biafra

Some days ago one of my sites certificate expired. I didn’t pay attention to the Let’s Encrypt periodic warning emails – I’m using the DNS-01 challenge.

I must create a simple script to check how many days are left and install it as a cron job.

After some search I found that curl and date could do it.

$ curl https://thejoyofstick.com -vI --stderr - | grep "expire date:" | cut -d: -f 2-
Jun 25 17:26:52 2022 GMT

$ date --date='Jun 25 17:26:52 2022 GMT' '+%s'
1656178012

$ date '+%s'
1649805603

$ echo '(1656178012-1649805603)/86400' | bc
73

We now have a way to calculate how many days are left.
You can build a bash script with these and, after checking for a countdown days threshold, send yourself a proper alert email.

For myself I’m using a perl script based on this one

#!/usr/bin/env perl

use strictures 2;
use IO::Socket::SSL;
use Net::SSLeay;
use Date::Simple ( 'date', 'today' );

my $site = shift || 'example.com';

my $client = IO::Socket::SSL->new("$site:443")
  or die "error=$!, ssl_error=$SSL_ERROR";
my $cert = $client->peer_certificate();
my $time = Net::SSLeay::X509_get_notAfter($cert);
my $asn_t = Net::SSLeay::P_ASN1_TIME_get_isotime($time);
my ($date) = split /T/, $asn_t;
my $diff = date($date) - today;
my $warning_time = 15;

print "Expire date: $date\n";
print "How many days left: $diff\n";
print "Warning before $warning_time days\n";

Added a personal email module to send a message if $diff is less than $warning_time and then cron with it.

Enjoy!

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Problem updating Chrome: Repository changed its ‘Origin’ value from ‘Google, Inc.’ to ‘Google LLC’

Posted on by Biafra

If you are using the Google repository to update your Chrome it doesn’t update anymore with apt-get due to security reasons.

Reading package lists... Done                      
E: Repository 'http://dl.google.com/linux/chrome/deb stable Release' changed its 'Origin' value from 'Google, Inc.' to 'Google LLC'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

The solution is fast. Just run

sudo apt update

Note that’s apt and not apt-get. And just accept the change.

Do you want to accept these changes and continue updating from this repository? [y/N]

Done!

Then just use again sudo apt-get update and sudo apt-get upgrade