firewall ports

Is there a good (easy) way to find out what port above 1023 are actually being used?

on my pix firewall I have a statment such as

access-list storein permit tcp host host gt 1023

my security auditors tell me I have to list the actual ports.


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Can You be more precise? What do You mean by "being used"?

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Michał Iwaszko

Well you could access-list storein permit tcp host YOURIP host ANY

All you need to do is a run a port scanner on host YOURIP to and see what pops up.

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Is this Microsoft Windows systems involved? If so, then gt 1023 is as often as specific as you are going to be able to get. Windows

-tends- to allocate the lowest unused port number from 1024 upwards, but it can get into the 60000+ range too.

The key to resolving this to the satisifaction of the security auditors is to note that dynamic port numbers as destinations do not occur in isolation in normal operations: when they occur, they occur as a result of a negotiation process that the PIX can often track and automatically open -just- the particular port. Particularily for tcp, since "permit tcp" is for opening new connections (whereas "permit udp" can sometimes be for getting around too-low timeouts on connections that have been opened from outside into the PIX, since udp is "stateless".)

You need to track down the process which is allocating the connection numbers dynamically, and ensuring that the PIX opens the appropriate ports automatically by way of an appropriate "fixup".

If you have PIX 4, PIX 5, or PIX 6, there are some circumstances under which the PIX cannot do this properly when using NETBIOS, Windows NT Authentication, Windows RPC, or plain "Sun RPC".

In particular, if you have Windows Exchange clients on your end, and the remote end of the link has Windows NT authentication and Windows Exchange 2000 Server, then you will never get this right, not unless you have experts running the Exchange systems that can nail down the ports very very precisely and tell you what they configured them as. (This is, for example, beyond the capacities of the five-person full-time Exchange team at my organization; there is a poster to who goes by Leythos who -claims- that his company routinely does this.) In the scenario I describe, remote NT authentication and remove Exchange 2000 server, unless you find an expert lock-downer, you *will* encounter problems unless you static NAT all your internal addresses individually to public IP addresses and you permit all tcp ports > 1023 in both directions between your desktops and the remote servers.

In -theory-, going for Exchange 2003 and LDAP solves those problems. Well, I shouldn't say "in theory": I should say that "The Exchange team assured me that [...]". In practice when we switched over to Exchange 2003, we still had inexplicables :(

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