[lvs-users] source hashing some times land on wrong server (with FTP)
pdm at pobox.com
Fri Nov 1 15:48:50 GMT 2019
We have FTP setup with on its own VIP and just map all ports (:0) and use
source hashing. Sometimes when the FTP client opens the data channel it
will land on the wrong real server causing a reset. I stress sometimes
because mostly FTP seems to work but we do see this behavior of requests
landing on the wrong server.
FTP client makes connection to VIP:0 on ftp port, is asked to open data
channel on VIP:0 on alternate port. FTP client sends SYN packet but that
packet doesn't land on the correct real FTP server, so connection is
reset. That SYN packet likely came through a different IPVS server but
should have sync connection state by this time.
Example of our config:
-A -t x.y.z.220:0 -s sh -p 600 -b sh-fallback
-a -t x.y.z.220:0 -r a.b.c.4:0 -i -w 1
-a -t x.y.z.220:0 -r a.b.c.5:0 -i -w 1
-a -t x.y.z.220:0 -r a.b.c.6:0 -i -w 1
-a -t x.y.z.220:0 -r a.b.c.7:0 -i -w 1
We have this config running on multiple active IPVS servers all running
active/backup sync processes .
We've also tried a non 1 weight (1000) to see if it was the overload logic
kicking in and sending requests to alt server, but that did not seem to be
Is there any reason why subsequent connections from the same source IP
would land on a different server?
More information about the lvs-users