How can I know the IP address was changed immediately ?

johnsee · 02-19-2009, 11:45 PM

Hello everyone, I have a question:

There are three hosts, A1, A2 and B,

First, B connected to A1 through TCP, and state is ESTABLISHED.
Now, I move the IP address from A1 to A2, that is to say,
A1 was changed to A2, B will connect to A2 after a while if B sent ARP request,
Ok, I know B will be failed and get the error message: connection reset by peer.
But, this case is what I want.

Code:

step1:  B  ------>  A1 ( 192.168.0.1)   #  ESTABLISHED

step2:  B  ------>  A1 (none)           #  hanging

step3:  B  ------>  A2 (192.168.0.1)    #  connection reset

-----------------------------------------------------------------------------------------
In another occasion, There are two hosts, A and B,
A has 2 IP address on eth0, IP1 and IP2, I create a TCP connection
from A(IP1) to A(IP2), and it's ESTABLISHED.
Now, I move the A(IP2) from A to B, that is to say,
B was changed to A, but A(IP1) never connect to B(IP2),
because this connection will not send ARP request,
it's always through local, so I would not get the error message,
and hanging about 12 minutes.

Code:

step1:  A (192.168.0.1)  ----->  A (192.168.0.2)    #  ESTABLISHED

step2:  A (192.168.0.1)  ----->  A (none)           #  hanging

step3:  A (192.168.0.1)  ----->  A (none)           #  hanging
                                 B (192.168.0.2)    #  no one will connect to this host

--------------------------------------------------------------------------------------
How can I know the IP address was changed immediately,
and I really want to get "connection reset by peer" in second case. :-)

Thank you in advance!

Mara · 02-22-2009, 03:13 PM

With kernel patch I see a way to solve the problem. Without that - only by forcing the connection in step 1 to get outside instead of being local.