WRT54G Incoming Log Destination Port 520

Question

I am trying to understand why an [Incoming Log Table] entry that recurs, i.e. in the page that presents itself when I navigate to the [Administration] Panel / [Log] Tab, and then click the [Incoming Log] button:
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Incoming Log Table
Source IP = 178.33.xxx.yyy
Destination Port Number = 520
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After I clear the Log (i.e. turn it off, save settings, turn it on again, save settings) the entry will reappear after a few days.
I have never seen any other incoming log entry.
Since it has been pressed into service several years ago, my WRT54G has been configured to block any and all incoming connections. The settings as they continue to appear (under the [Security] Panel / [Firewall] Tab) are:
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Checked (Yes) = [Block Anonymous Internet Requests]
Checked (Yes) = [Filter Multicast]
Checked (Yes) = [Filter Internet NAT Redirection]
Checked (Yes) = [Filter IDENT (Port 113)]
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I continue to have disabled all port forwarding, port triggering, the DMZ, and QoS, via the applicable tabs under the [Applications & Gaming] Panel. The WRT54G continues to be configured to operate as a Gateway (via the [Settings] Panel/[Advanced Routing] Tab). No static routes are defined. The routing table show four entries, none of which are remarkable or match in anyway the partial address identified above.
So I am under the impression that my WRT54G should be ignoring everything from the WAN-side.
Even pinging the WAN-side of my router from the outside internet times out.
My WRT54G ver 6 is at firmware level 1.02.8, which, as far as I can tell is the latest issued by Cisco.
I am completely perplexed how such a connection is being established, and do not know if it is or has the potential of causing any harm. My own research indicates port 520 is typically used for RIP protocol, but I have almost zero knowledge of such.
I certainly appreciate any elucidation.
My thanks for your attention.

Answer 1

bonski wrote:
Forgive me if I seem flippant, but I am not sure what kind of "glitch" you are looking to correct. If performing a factory reset procedure were already known to correct a specific problem, then I would seriously consider it. If performing a factory reset did not run the risk of injecting more problems through the process of having to redo firmware updates and settings, then I would seriously consider it. I am truly seeking insight into understanding the nature of the symptoms, and why they may be occurring. I am not looking for trial and accidental success.
Thank you for you thoughts.
Hi bonski,
The log means that the IP:  178.33.xxx.yyy (which is from your ISP) sends logs to port 520. Port 520 is your router. I believe it is saying that you ISP simply sends data to your router. This is normal since your router gets internet connection from the ISP. This is by the way base on my understanding about the research I've made.
This might help:
http://www.pc-library.com/ports/tcp-udp-port/520/
http://www.auditmypc.com/udp-port-520.asp
http://www.iss.net/security_center/advice/Exploits/Ports/520/default.htm