Port Scanning Prevention Filter sometimes blocks port 80 Requests (2012 R2)

arthurh88 used Ask the Experts™
Ok so in my event log, I sometimes get this error:  
The Windows Filtering Platform has blocked a packet.

Application Information:
      Process ID:            0
      Application Name:      -

Network Information:
      Direction:            Inbound
      Source Address:            50.99.999.99
      Source Port:            64618
      Destination Address:
      Destination Port:            80
      Protocol:            6

Why would my firewall have any instances where it would be blocking port 80, I wondered.   This happens seemingly at random.   I did a netsh wfp capture start.   And found this entry for that IP:

I then searched for FilterID 88382 and found it defined as this:

      <name>Port Scanning Prevention Filter</name>
      <description>This filter prevents port scanning.</description>

When I looked up the Port Scanning Prevention Filter, I learned that it cannot be disabled and its function is that if a port doesn't have an application "listening" on it, then windows firewall will drop the packet regardless.   http://superuser.com/questions/362358/how-to-disable-hidden-windows-firewall-filter 

Based on this definition, it seems like my IIS web service has brief periods of "not listening" and when a user connects to port 80, IIS isn't listening in that single moment, and the packet gets dropped....could this be happening?    That is what it appears like on the surface if I understand all this right.

This raises my concern...why would my firewall sometimes think that port 80 isn't listening?  The server is a web server.   I'm stumped at where else to go in my diagnostics.  I'd like to know why windows filtering is occasionally (and this is only sometimes) dropping port 80 packets.  Is there a way I can diagnose IIS to see if it occasionally...even for milisecond periods of time...stops "listening?"
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Brian MurphySenior Information Technology Consultant

Port conflict?

Are you running Work Folders? and IIS?


i dont know.  how can i find that out?   interesting theory, I didn't think to check for something else listening on port 80.   is there a command that will show what apps are listening on a port?


I'm running IIS
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i ran a netstat -nao  and found port 80 only has entires like this:
 TCP         24.999.99.999:53019    ESTABLISHED     4
 TCP         24.999.99.999:53020    ESTABLISHED     4
 TCP       24.999.99.9997:53021    ESTABLISHED     4
 TCP      TIME_WAIT       0
 TCP      TIME_WAIT       0
 TCP      TIME_WAIT       0
Top Expert 2016

you should run your server behind a router so it is not directly connected to the internet.


it is behind a hardware router, it is not directly connected to the internet.  these packets on port 80 are already through the external router  (router lets port 80 pass worldwide)
Distinguished Expert 2017

The filter you mention seems to enforce a connection count based restriction that is set too low for your needs.

Based in your netstat output it suggest you are limiting port 80 using this filter to a max of 3 connections from the same source.
Usually, when http requests come they do in two ways one is using a single connection to request the pages and any and all object using multi pipelining. However, more commonly, each object on a page is obtained by a single connection. So if your page has 10 images, and additional files, the same source IP will hit your IIS server at least 10 times within a second.

You likely need to exempt port 80/443 from that filter whose purpose is to detect port scanning meaning the same ip tries to connect to multiple/sequential ports on your system.
Mohammed KhawajaManager - Infrastructure:  Information Technology

You should be running your server behind a firewall and have a rule which will forward requests for port 80 to an internal IP address.  

To find out what is listening on port 80, you could run the following command:
netstat -aon -b

You could also use the PID ID and find the executable from Task Manager as to which directory it resides on.
Distinguished Expert 2017
According to the Asker there is an external firewall that is configured to port forward, the person seems to also have windows firewall enabled and that is where the issue is, the person is using on the software firewall port scanning filter which triggers when there are a count of requests from the same IP different port. The fillter for port scanning should detect same IP same port going to different ports on the local system as a port scan.

The other possiblity is that the filter for port scanning is being applied on the outgoing response side, only way to confirm is to use wireshark or microsoft network tool to look at the traffic on the server to see whether the request is being allowed through but the response is being block by the windows firewall.
Another option is to use nmap on the local system and trigger a scan on an external IP of 10-20 ports to see whether the same event will be recorded in the event log and this filter.

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