I'm trying to convert my CSM load-balancing environment from directed to dispatch mode. I've had success with normal telnet traffic but run into problems with FTP.
My real servers are layer-2 adjacent to the switch.
My config looks like this:
ip slb vlan 19 client
ip address 188.8.131.52 255.255.240.0
ip slb vlan 9 server
ip address 184.108.40.206 255.255.240.0
no nat server
no nat client
virtual 220.127.116.11 tcp ftp service ftp
I've put a sniffer on the server side vlan and I can see this pattern:
1) Client SYN pkt goes through CSM, gets
routed to server.
2) Server responds with SYN/ACK, but this packet goes directly back to the client (not through the CSM, because I'm not NATing)
3) Client responds with the final ACK, which goes to the CSM, but the CSM eats the packet. When I turn on debug module csm 11 ftp, I see that each time the final ACK is received by the CSM, it outputs these lines:
May 4 20:48:06.758 UTC: CSM11: called slowpath_ftp_rx
May 4 20:48:06.758 UTC: CSM11: no session for ftp rx
In TCP 19 18.104.22.168:1131 22.214.171.124:21 ESTAB
Why doesn't the ACK get processed and sent to the correct server by the CSM?
One additional note: I also tried this same scenario but without specifying 'service ftp' on the virtual server defintion. In that case, the control connection comes up fine but any attempt to bring up a data connection fails (times out). But then again, that's the whole point of 'service ftp', right?
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