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strange port communication

Posted on 2013-01-04
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Last Modified: 2013-01-22
Hi,
I have two computer communicating (one inside the network, the other on the outside the network).

The are both using strange port numbers that are not commonly used.  (Port 52497 for the external IP address and 9678 internally)

My question is
1. Shouldn't the firewall  be configured to prevent outgoing ports except for typical ports (80, 443, etc?)
2. Should the firewall be configured to only allow in commonly used ports (port 80, 443)?

Thanks.
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Question by:NYGiantsFan
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4 Comments
 
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by:brokenbyte
brokenbyte earned 125 total points
ID: 38744815
1. Most firewalls allow outgoing traffic through most ports, especially when the traffic is initiated internally as a request, which might then be sent out on a different port, depending on the service.

The default action for a firewall is to block all unsolicited traffic coming in to your network.

2. Even if you configure a firewall to allow say, port 80, 443, 3389, to come in as an example, the originating port could be a random port (such as 52497 in your case.) The important port is the *destination*. And that is the port that is the focus when setting up your firewall rules.
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LVL 13

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by:Ugo Mena
Ugo Mena earned 250 total points
ID: 38744852
Port 9678 is registered to EMC2 (Legato) Networker or Sun Solcitice Backup (Official) processes. Do you know if any of these backup services are supposed to be running to/from your network?

Depending on the type of firewall in your environment, most of the outgoing ports are going to be open to allow internal clients to connect to various external resources. Unless you are hosting a site/application/etc from your local network, almost all of the incoming ports to your network should be closed by the firewall to prevent incoming connections.

To get a better indication of who you are connecting to, you should check for the external IP address and then check it against whois
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by:
Ugo Mena earned 250 total points
ID: 38744866
Could also be someone streaming Quicktime content.
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by:giltjr
giltjr earned 125 total points
ID: 38745003
Some protocols also negotiate to use different ports.  Example: FTP.  

FTP has two connections, a command/control connection and a data connection.  

There are two types of data connections: active and passive.  If doing active FTP, the server initiates a outbound connection to the client from port 20 to a random high port.  When doing active the client tells the server what port it is listening on buy the FTP PORT/EPRT commands over the command/control connections.

 If doing passive the client initiates a connection to the server from a random high port to a random high port.   In this situation the server tells the client what port it will be listening on using the PASV/EPSV commands.

Most firewalls "listen" in on the command/control connection (typically port 21) for the PORT/EPRT/PASV/EPSV commands and dynamically create a rule to allow the data connection.   Once the transfer is done, based on the data connection being reset, the firewall dynamically removes this rule.

I believe there are other protocols/products that do this also.
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