Re: TCP/IP redundant connections
Artem Kazakov wrote: So I want to utilize IP-sharing and TCP-connection synchronization (which is not yet implemented by anyone as far as I know). I want it in case of failure seamlessly to switch to the other machine. As far as the internal state is synchronized, if it is possible to synchronize open connections as well(and all the low level stuff as packet sequence numbers and so on) it would allow to make switch-over to the back-up server in a matter of seconds, and the clients would stay connected. I don't know if you already considered this, but the above looks like both machines would simultaneously process a single TCP connection. So, when a TCP connection request (handshake) arrives, you want both of the machines to respond? Further on: You'll confuse the remote application and waste bandwidth if you send two responses to every TCP packet you receive. And on: What about the applications running on the two machines: if the remote client send e.g. a request to delete a resource (just an example): would both servers receive and respond to the request? etc, etc. Have you read the manual for carp(4) and why isn't CARP good enough for what you need? signature.asc Description: OpenPGP digital signature
Re: TCP/IP redundant connections
On Tuesday 11 September 2007, Artem Kazakov wrote: Hello Everyone! For my research project I'm working on making some network services redundant. And I have one idea, but I'm not so good and operating system internals, so could you please tell what do you think. If it is possible at all. So, I have two hosts, which are all the same and they have some network service which I need to make available all the time. This service has some internal state, which is synchronized over private connection. And at one time only one of the servers actually works with clients, the other on is just sitting there and kept synchronized. The clients have persistent TCP connections to the server, and in case of failure they make UDP broadcasts searching for server and then reconnect. So basically there is no need to use IP-sharing between two of them. But if the server fails, the client usually notices that after some time-out (tcp keep alive time out I suppose) which is not very good in some cases. So I want to utilize IP-sharing and TCP-connection synchronization (which is not yet implemented by anyone as far as I know). I want it in case of failure seamlessly to switch to the other machine. As far as the internal state is synchronized, if it is possible to synchronize open connections as well(and all the low level stuff as packet sequence numbers and so on) it would allow to make switch-over to the back-up server in a matter of seconds, and the clients would stay connected. Is is possible to do so ? And if yes, how difficult would it be for a person who has solid background in general-tasks programming, but no experience with low level system programming ? And what are the possible cave-eats of this approach? TCP is a reliable protocol. That means once you ACK a segment the other side assumes that you have actually received it. In your scenario, that would mean to defer the ACK until the secondary box has received the copy of the segment and acknowledged to the first one which then in turn will acknowledge the client. As a result you are back to a single point of failure and greatly diminished performance. If you try to do it differently - e.g. have the second box just snoop in on the TCP state. There is no guarantee that it has actually seen every packet and once a segment (that the primary has ACKed) is lost, there's no way to get it back. I think you should rather look at session management in the application and move away from long-lived TCP connections for that purpose. -- /\ Best regards, | [EMAIL PROTECTED] \ / Max Laier | ICQ #67774661 X http://pf4freebsd.love2party.net/ | [EMAIL PROTECTED] / \ ASCII Ribbon Campaign | Against HTML Mail and News signature.asc Description: This is a digitally signed message part.
TCP/IP redundant connections
Hello Everyone! For my research project I'm working on making some network services redundant. And I have one idea, but I'm not so good and operating system internals, so could you please tell what do you think. If it is possible at all. So, I have two hosts, which are all the same and they have some network service which I need to make available all the time. This service has some internal state, which is synchronized over private connection. And at one time only one of the servers actually works with clients, the other on is just sitting there and kept synchronized. The clients have persistent TCP connections to the server, and in case of failure they make UDP broadcasts searching for server and then reconnect. So basically there is no need to use IP-sharing between two of them. But if the server fails, the client usually notices that after some time-out (tcp keep alive time out I suppose) which is not very good in some cases. So I want to utilize IP-sharing and TCP-connection synchronization (which is not yet implemented by anyone as far as I know). I want it in case of failure seamlessly to switch to the other machine. As far as the internal state is synchronized, if it is possible to synchronize open connections as well(and all the low level stuff as packet sequence numbers and so on) it would allow to make switch-over to the back-up server in a matter of seconds, and the clients would stay connected. Is is possible to do so ? And if yes, how difficult would it be for a person who has solid background in general-tasks programming, but no experience with low level system programming ? And what are the possible cave-eats of this approach? Thank you. Artem Kazakov. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to [EMAIL PROTECTED]