At 11:08 AM 5/2/02, Mark Odette II wrote: >Tamas- Thank you for your reply. > >Could you or anyone else explain in more indepth terms what is or what >causes a Half-Closed TCP session??
There are a number of states that a TCP connection can be in per the RFC for TCP (793). "Half-closed" is not one of them, however... But my guess is that "half-closed" refers to the state that the RFC would call "half-open." An established connection is said to be "half-open" if one of the sides has closed or aborted the connection at its end without the knowledge of the other, or if the two ends of the connection have become desynchronized because of a crash. Such connections will automatically become reset if an attempt is made to send data in either direction. Another possibility is that "half-closed" refers to one of the states that occurs at the normal end of a session: FIN-WAIT-1 - represents waiting for a connection termination request from the remote TCP, or an acknowledgment of the connection termination request previously sent. FIN-WAIT-2 - represents waiting for a connection termination request from the remote TCP. CLOSE-WAIT - represents waiting for a connection termination request from the local user. CLOSING - represents waiting for a connection termination request acknowledgment from the remote TCP. These states (and the half-open state) should be temporary, but if they aren't, then they can leave a host slightly vulnerable to attack. The host may use up resources that it really no longer needs. I know this is a lot of theory to throw at you, but hopefully it will relate somehow to your problem. ;-) For even more info about the TCP states, see RFC 793. Priscilla >Correct me if I'm wrong, but for the Connection Slot, this refers to TCP >connections between two nodes, such as a Windows workstation running an >application to connect to a Server Application Server, and the connectios >are between specific and random ports above 1024 simultaneously!?! Do I >understand that correctly? > > >I'm sure our famous question is starting to surface in many folks' minds: >"What problem are you trying to solve?" > >That problem is with users on workstations at remote locations connecting to >an application server (located at the other end of a PIX-to-PIX VPN Tunnel >at the "main" office) and at random, they get disconnected from the >server... but Internet access continues to work at the same time. In short, >it appears that there is something happening with sessions across the VPN >tunnel for users that go idle for a varying window of time. Just yesterday, >I was reported that at one of the remote locations (and there are 3, which >all suffer the same exact problem), one user "worked straight through lunch, >while everyone else who used the same application went to lunch. End result >was that the continuous worker did not get "kicked" out of the system, but >all the other users that left the application open and when to lunch did." > >So, I'm trying to chase down what the issue might be, short of putting a >Sniffer at the main location to see if I can identify the problem there. I >suspect that there is something I need to adjust with the Timeout settings >on the PIX, but did not want to make changes without understanding the >pros/cons/implications of what I was doing. > >Unfortunately, the PIX Command Reference for 6.1, CCO, and most of Tamas's >explanation were exactly what I found, and nothing more.... Tamas, thank you >for at least giving me a little more info! > >I even searched Google for a definition of "half-closed session", but got no >definitiion hits... just lots of pages (mostly Cisco) mentioning the phrase >amidst other topics. :( > >Any help is appreciated. > >Thanks >Mark > >-----Original Message----- >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of >HORVATH TAMAS >Sent: Thursday, May 02, 2002 7:41 AM >To: [EMAIL PROTECTED] >Subject: RE: Definition of terms... Do you know the answer?? [7:43090] > > >Hi! > >timeout xlate: Idle time until a translation slot if freed. > >timeout conn: Idle time until a connection slot is freed. > >There is a distinction made between translated sessions (produced by nat, >global, static, access-list, access-group commands)and connected sesssions >when discussing the PIX firewall. Translations are at the IP layer, >connections are at the transport layer. You cab have many connections open >under one translation. > >timeout half-closed: Idle time until a TCP half-close connection is freed. > >timeout udp: Idle time until an UDP slot is freed. > >timeout rpc: Idle time until an UDP slot is freed. > >If a given slot has not been used for the idle time specified, the resource >is returned to the free pool. > >So one purpose of these commands is resource management. Another purpose is >to provide the 'Adaptive' part of the ASA, as the unused ports will be >closed. > >Best regards, > > Tamas Horvath > network engineer > Tel.: +36 22/515-452, > Fax: +36 22/327-532 > E-Mail: [EMAIL PROTECTED] >Message-ID: >From: Mark Odette II >Reply-To: Mark Odette II >To: [EMAIL PROTECTED] >Subject: Definition of terms... Do you know the answer?? [7:43090] >Date: Thu, 2 May 2002 07:29:44 +0200 >MIME-Version: 1.0 >X-Mailer: Internet Mail Service (5.5.2650.21) >Content-Type: text/plain; charset="iso-8859-2" > >Folks, I've been trying to find the answer to a couple of questions I have, >and unfortunately, my patience is thin at the moment due to a really bad >allergy attach, which in turn is making me barely be able to stay at the >computer.... but I've got to solve a problem. > >So, could someone give me the low-down on what the following terms/settings >really mean in relation to TCP/UDP communications? > >These terms are related to settings on a Firewall (PIX or Router), and >explanations relating to such would really help me understand their >purpose/functionality. Thanks in Advance!! > >timeout xlate > >timeout conn > >timeout half-closed > >timeout udp > >timeout rpc > > >I've got what I believe is a solid idea of what the first one, and perhaps >the second one covers... but someone formally explaining them all will make >me, and I'm sure many others benefit. > >Thanks, >Mark ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=43142&t=43090 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
