Connection Cache

Unanswered Question
Jul 11th, 2007

Most servers are blocked by the access list. If a server is allowed to bypass the access list and a connection is created. Where does the connection cached in the FWSM?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (3 ratings)
Jon Marshall Wed, 07/11/2007 - 12:37


If i understand you correctly the FWSM will keep the connection record in it's state table for as long as the connection is active.

Is there something more specific you were looking for ?


nguyenvinht Wed, 07/11/2007 - 13:03

What is exactly in the state table? Is there a way I can view the state table? I have other questions after this but first I neeed to understand this step first. Thanks in advance for your reply.

Jon Marshall Wed, 07/11/2007 - 13:11

As far as i know the way to view the present state table is to do a "sh conn" on your FWSM. This will show you all the current connections the FWSM is keeping track of and if TCP connections the TCP flags.

Edit - sorrydidn't answer the first bit. The state table is how a stateful firewall keeps track of connections. So a simple example would

client on inside telnets to a server on outside. FWSM records the client IP address, the client port number, the destination IP address, the destination port number (which will be 23 in this case) and the TCP flag which for the initial packet will be a SYN flag.

When the server responds the TCP flag will be a SYN/ACK and because the firewall has an entry in it's state table for the corresponding SYN it will allow it through.

Note that if a server on the outside sent a SYN/ACK packet but there was no corresponding SYN packet in it's state table it would drop the packet.


nguyenvinht Wed, 07/11/2007 - 13:44


If there is a connection from inside server to outside server on port 23. The traffic is flowing. The flow is recorded in the state table. What will happen if another connection is opened from server to another outside server by telnet or ftp? Now what is recorded in the state table?

Will these two statements recorded in the state table?> on port 23> on port 23

If this happen, does this kill the flow from to


Jon Marshall Wed, 07/11/2007 - 22:45


No it doesn't kill the flow because all the information is recorded in the state table. So in your example the destination address is different so it the 2 connections can be seen as separate int the state table.

But let's go one further opens a telnet connection to open an ssh connection to

Both these are also separate -> 23 -> 22

And one step further opens a telnet connection to opens another telnet connection to

Again these are kept separate because although i haven't included them in the examples so far, the source port is also recorded so 2551 23 2661 23

Hope this makes sense



This Discussion