What IP address is this log entry coming from? (Is "::" a valid IP address?) (Apache Users)

What IP address is this log entry coming from? (Is "::" a valid IP address?)

Date Prev

Date Next

Thread Prev

Thread Next

Date Index

Thread Index

To: users@xxxxxxxxxxxxxxxx

Subject: What IP address is this log entry coming from? (Is "::" a valid IP address?)

From: Apache Issues <apacheissues@xxxxxxxxx>

Date: Mon, 30 Aug 2010 16:00:34 -0700 (PDT)

Reply-to: users@xxxxxxxxxxxxxxxx

I'm using:

CustomLog "/var/log/apache2/access_log" "%a %l %u %t \"%r\" %>s %b \"%{Referer}i\""

And I occasionally see this right around the time the CPU starts running at 100%:

:: - - [27/Aug/2010:12:28:01 -0700] "GET /favicon.ico HTTP/1.1" 200 - "-"

%a is supposed to be an IP address, so what IP address is "::"? I'm only somewhat familiar with IPv6 but I've never seen "::" before.

I'm attempting to try to figure out why, on random occasions, the server CPU suddenly spikes to 100%. I'm not sure where the problem lies. Could be Apache, MySQL, PHP, or something else (e.g. the OS). This problem has been ongoing for months now and the only "fix" is to reboot the box, which is a rather frustrating "solution". The "::" issue is the first possible clue I've gotten. It seems to crop up only around the times the server is at 100% in the logs.