[lvs-users] TCP Retransmissions?

housey at sme-ecom.co.uk housey at sme-ecom.co.uk
Wed Jun 26 13:55:31 BST 2013


Ive been looking into LVS to help balance load amongst some SMTP 

I have set up a test LVS system in front of 3 real SMTP servers.

I'm using direct routing and have used the iptables method on all 3 
real servers to overcome any arp issues

i.e. iptables -t nat -A PREROUTING -p tcp -d <vip> --dport 25 -j 

My testing seems to be going well and I can see traffic being balanced 
between the 3 servers, however I ran tcpdump on the lvs server just to 
look at the traffic and noticed im getting lots of TCP Retransmission 
and some TCP Dup ACK's

I ran tcpdump on a normal SMTP server and don't see anywhere near as 

Can someone lend me their experience and advise if this something I 
need to worry about and investigate further?



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